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Intermittent hypoxia, or intermittent low oxygen interspersed with normal oxygen levels, has differential effects that depend on the "dose" of hypoxic episodes (duration, severity, number per day, and number of days). Whereas "low dose" daily acute intermittent hypoxia (dAIH) elicits neuroprotection and neuroplasticity, "high dose" chronic intermittent hypoxia (CIH) similar to that experienced during sleep apnea elicits neuropathology. Sleep apnea is comorbid in >50% of patients with Alzheimer's disease--a progressive, neurodegenerative disease associated with brain amyloid and chronic Tau dysregulation (pathology). Although patients with sleep apnea present with higher Tau levels, it is unknown if sleep apnea through attendant CIH contributes to onset of Tau pathology. We hypothesized CIH characteristic of moderate sleep apnea would increase dysregulation of phosphorylated Tau (phospho-Tau) species in Sprague-Dawley rat hippocampus and prefrontal cortex. Conversely, we hypothesized that dAIH, a promising neurotherapeutic, has minimal impact on Tau phosphorylation. We report a dose-dependent intermittent hypoxia effect, with region-specific increases in 1) phospho-Tau species associated with human Tauopathies in the soluble form and 2) accumulated phospho-Tau in the insoluble fraction. The latter observation was particularly evident with higher CIH intensities. This important and novel finding is consistent with the idea that sleep apnea and attendant CIH have the potential to accelerate the progression of Alzheimer's disease and/or other Tauopathies. NEW & NOTEWORTHY Sleep apnea is highly prevalent in people with Alzheimer's disease, suggesting the potential to accelerate disease onset and/or progression. These studies demonstrate that intermittent hypoxia (IH) induces dose-dependent, region- specific Tau phosphorylation, and are the first to indicate that higher IH "doses" elicit both endogenous, (rat) Tau hyperphosphorylation and accumulation in the hippocampus. These findings are essential for development and implementation of new treatment strategies that minimize sleep apnea and its adverse impact on neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Cerebral hypoxia is a serious consequence of several cardiorespiratory illnesses. Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into cerebral hypoxia in critical illness. In addition, although sex-specific differences in cardiovascular diseases are strongly supported, few have focused on differences in ocular blood flow. We evaluated the retinal microvasculature in males (n = 11) and females (n = 7) using functional optical coherence tomography at baseline (1,130 m) (day 0), following rapid ascent (day 2), and prolonged exposure (day 9) to high altitude (3,800 m). Retinal vascular perfusion density (rVPD; an index of total blood supply), retinal thickness (RT; reflecting vascular and neural tissue volume), and arterial blood were acquired. As a group, rVPD increased on day 2 versus day 0 (P < 0.001) and was inversely related to PaO2 (R² = 0.45; P = 0.006). By day 9, rVPD recovered to baseline but was significantly lower in males than in females (P = 0.007). RT was not different on day 2 versus day 0 (P > 0.99) but was reduced by day 9 relative to day 0 and day 2 (P < 0.001). RT changes relative to day 0 were inversely related to changes in PaO2 on day 2 (R² = 0.6; P = 0.001) and day 9 (R² = 0.4; P = 0.02). RT did not differ between sexes. These data suggest differential time course and regulation of the retina during rapid ascent and prolonged exposure to high altitude and are the first to demonstrate sex-specific differences in rVPD at high altitude. The ability to assess intact microvasculature contiguous with the brain has widespread research and clinical applications. NEW & NOTEWORTHY Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into consequence of cerebral hypoxia in critical illness. This study demonstrates dynamic regulation of the retina during rapid ascent and prolonged exposure to high altitude and is the first to demonstrate sex-specific differences in retinal microvasculature at high altitude. The ability to dynamically assess intact microvasculature contiguous with the brain has widespread research and clinical applications. [ABSTRACT FROM AUTHOR]

The changes in brain perfusion and oxygenation in critical illness, which are thought to contribute to brain dysfunction, are unclear due to the lack of methods to measure these variables. We have developed a technique to chronically measure cerebral tissue perfusion and oxygen tension in unanesthetized sheep. Using this technique, we have determined the changes in cerebral perfusion and PO2 during the development of ovine sepsis. In adult Merino ewes, fiber-optic probes were implanted in the brain, renal cortex, and renal medulla to measure tissue perfusion, oxygen tension (PO2), and temperature, and flow probes were implanted on the pulmonary and renal arteries. Conscious sheep were infused with live Escherichia coli for 24 h, which induced hyperdynamic sepsis; mean arterial pressure decreased (from 85.2 ± 5.6 to 71.5 ± 8.7 mmHg), while cardiac output (from 4.12 ± 0.70 to 6.15 ± 1.26 L/min) and total peripheral conductance (from 48.9 ± 8.5 to 86.8 ± 11.5 mL/min/mmHg) increased (n = 8, all P < 0.001) and arterial PO2 decreased (from 104 ± 8 to 83 ± 10 mmHg; P < 0.01). Cerebral perfusion tended to decrease acutely, although this did not reach significance, but there was a significant and sustained decrease in cerebral tissue PO2 (from 32.2 ± 10.1 to 18.8 ± 11.7 mmHg) after 3 h and to 22.8 ± 5.2 mmHg after 24 h of sepsis (P < 0.02). Sepsis induced large reductions in both renal medullary perfusion and PO2 but had no effect in the renal cortex. In ovine sepsis, there is an early decrease in cerebral PO2 that is maintained for 24 h despite minimal changes in cerebral perfusion. Cerebral hypoxia may be one of the factors causing sepsis-induced malaise and lethargy. [ABSTRACT FROM AUTHOR]

Chronic hypoxia (CH) augments basal and endothelin-1 (ET-1)-induced pulmonary vasoconstrictor reactivity through reactive oxygen species (ROS) generation and RhoA/Rho kinase (ROCK)-dependent myofilament Ca2+ sensitization. Because ROCK promotes actin polymerization and the actin cytoskeleton regulates smooth muscle tension, we hypothesized that actin polymerization is required for enhanced basal and ET-1-dependent vasoconstriction after CH. To test this hypothesis, both end points were monitored in pressurized, endothelium-disrupted pulmonary arteries (fourth-fifth order) from control and CH (4 wk at 0.5 atm) rats. The actin polymerization inhibitors cytochalasin and latrunculin attenuated both basal and ET-1-induced vasoconstriction only in CH vessels. To test whether CH directly alters the arterial actin profile, we measured filamentous actin (F-actin)-to-globular actin (G-actin) ratios by fluorescent labeling of F-actin and G-actin in fixed pulmonary arteries and actin sedimentation assays using homogenized pulmonary artery lysates. We observed no difference in actin polymerization between groups under baseline conditions, but ET-1 enhanced actin polymerization in pulmonary arteries from CH rats. This response was blunted by the ROS scavenger tiron, the ROCK inhibitor fasudil, and the mDia (RhoA effector) inhibitor small-molecule inhibitor of formin homology domain 2. Immunoblot analysis revealed an effect of CH to increase both phosphorylated (inactive) and total levels of the actin disassembly factor cofilin but not phosphorylated cofilin-to-total cofilin ratios. We conclude that actin polymerization contributes to increased basal pulmonary arterial constriction and ET-1-induced vasoconstrictor reactivity after CH in a ROS- and ROCK-dependent manner. Our results further suggest that enhanced ET-1-mediated actin polymerization after CH is dependent on mDia but independent of changes in the phosphorylated cofilin-to-total cofilin ratio. NEW & NOTEWORTHY This research is the first to demonstrate a role for actin polymerization in chronic hypoxia-induced basal pulmonary arterial constriction and enhanced agonist-induced vasoconstrictor activity. These results suggest that a reactive oxygen species- Rho kinase-actin polymerization signaling pathway mediates this response and may provide a mechanistic basis for the vasoconstrictor component of pulmonary hypertension. [ABSTRACT FROM AUTHOR]

Endothelial dysfunction in chronic hypoxia (CH)-induced pulmonary hypertension is characterized by reduced store-operated Ca2+ entry (SOCE) and diminished Ca2+- dependent production of endothelium-derived vasodilators. We recently reported that SOCE in pulmonary arterial endothelial cells (PAECs) is tightly regulated by membrane cholesterol and that decreased membrane cholesterol is responsible for impaired SOCE after CH. However, the ion channels involved in cholesterol-sensitive SOCE are unknown. We hypothesized that cholesterol facilitates SOCE in PAECs through the interaction of Orai1 and stromal interaction molecule 1 (STIM1). The role of cholesterol in Orai1-mediated SOCE was initially assessed using CH exposure in rats (4 wk, 380 mmHg) as a physiological stimulus to decrease PAEC cholesterol. The effects of Orai1 inhibition with AnCoA4 on SOCE were examined in isolated PAEC sheets from control and CH rats after cholesterol supplementation, substitution of endogenous cholesterol with epicholesterol (Epichol), or vehicle treatment. Whereas cholesterol restored endothelial SOCE in CH rats, both Epichol and AnCoA4 attenuated SOCE only in normoxic controls. The Orai1 inhibitor had no further effect in cells pretreated with Epichol. Using cultured pulmonary endothelial cells to allow better mechanistic analysis of the molecular components of cholesterol-regulated SOCE, we found that Epichol, AnCoA4, and Orai1 siRNA each inhibited SOCE compared with their respective controls. Epichol had no additional effect after knockdown of Orai1. Furthermore, Epichol substitution significantly reduced STIM1-Orai1 interactions as assessed by a proximity ligation assay. We conclude that membrane cholesterol is required for the STIM1-Orai1 interaction necessary to elicit endothelial SOCE. Furthermore, reduced PAEC membrane cholesterol after CH limits Orai1-mediated SOCE. [ABSTRACT FROM AUTHOR]

ΔFosB is a member of the activator protein-1 family of transcription factors. ΔFosB has low constitutive expression in the central nervous system and is induced after exposure of rodents to intermittent hypoxia (IH), a model of the arterial hypoxemia that accompanies sleep apnea. We hypothesized ΔFosB in the nucleus of the solitary tract (NTS) contributes to increased mean arterial pressure (MAP) during IH. The NTS of 11 male Sprague-Dawley rats was injected (3 sites, 100 nl/site) with a dominant negative construct against ΔFosB (ΔJunD) in an adenoassociated viral vector (AAV)-green fluorescent protein (GFP) reporter. The NTS of 10 rats was injected with AAV-GFP as sham controls. Two weeks after NTS injections, rats were exposed to IH for 8 h/day for 7 days, and MAP was recorded using telemetry. In the sham group, 7 days of IH increased MAP from 99.8 ± 1.1 to 107.3 ± 0.5 mmHg in the day and from 104.4 ± 1.1 to 109.8 ± 0.6 mmHg in the night. In the group that received ΔJunD, IH increased MAP during the day from 95.9 ± 1.7 to 101.3 ± 0.4 mmHg and from 100.9 ± 1.7 to 102.8 ± 0.5 mmHg during the night (both IH-induced changes in MAP were significantly lower than sham, P < 0.05). After injection of the dominant negative construct in the NTS, IH-induced ΔFosB immunoreactivity was decreased in the paraventricular nucleus (P < 0.05); however, no change was observed in the rostral ventrolateral medulla. These data indicate that ΔFosB within the NTS contributes to the increase in MAP induced by IH exposure. [ABSTRACT FROM AUTHOR]

Tolerance to central hypovolemia is highly variable, and accumulating evidence suggests that protection of anterior cerebral blood flow (CBF) is not an underlying mechanism. We hypothesized that individuals with high tolerance to central hypovolemia would exhibit protection of cerebral oxygenation (ScO2), and prolonged preservation of CBF in the posterior vs. anterior cerebral circulation. Eighteen subjects (7 male/11 female) completed a presyncope-limited lower body negative pressure (LBNP) protocol (3 mmHg/min onset rate). ScO2 (via near-infrared spectroscopy), middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv) (both via transcranial Doppler ultrasound), and arterial pressure (via finger photoplethysmography) were measured continuously. Subjects who completed ≤ 70 mmHg LBNP were classified as high tolerant (HT; n = 7) and low tolerant (LT; n = 11) if they completed <60 mmHg LBNP. The minimum difference in LBNP tolerance between groups was 193 s (LT = 1,243 ± 185 s vs. HT = 1,996 ± 212 s; P < 0.001; Cohen's d = 3.8). Despite similar reductions in mean MCAv in both groups, ScO2 decreased in LT subjects from -15 mmHg LBNP (P = 0.002; Cohen's d=1.8), but was maintained at baseline values until -75 mmHg LBNP in HT subjects (P < 0.001; Cohen's d = 2.2); ScO2 was lower at -30 and -45 mmHg LBNP in LT subjects (P ≤ 0.02; Cohen's d ≥ 1.1). Similarly, mean PCAv decreased below baseline from -30 mmHg LBNP in LT subjects (P = 0.004; Cohen's d = 1.0), but remained unchanged from baseline in HT subjects until -75 mmHg (P = 0.006; Cohen's d = 2.0); PCAv was lower at -30 and -45 mmHg LBNP in LT subjects (P ≤ 0.01; Cohen's d ≥ 0.94). Individuals with higher tolerance to central hypovolemia exhibit prolonged preservation of CBF in the posterior cerebral circulation and sustained cerebral tissue oxygenation, both associated with a delay in the onset of presyncope. [ABSTRACT FROM AUTHOR]

Exposure to acute high-altitude hypoxia is associated with an increase in cerebral blood flow (CBF) as a consequence of low arterial O2 tension. However, in response to high altitude acclimatization, CBF returns to levels similar to those at sea level, and tissue blood flow is maintained by an increase in angiogenesis. Of consequence, dysregulation of the acclimatization responses and CBF can result in acute mountain sickness, acute cerebral and/or pulmonary edema. To elucidate the signal transduction pathways involved in successful acclimatization to high altitude, in ovine carotid arteries, we tested the hypothesis that high altitude-associated long-term hypoxia results in changes in gene expression of critical signaling pathways. We acclimatized nonpregnant adult sheep to 3,801 m altitude for 110 days and conducted oligonucleotide microarray experiments on carotid arteries. Of a total of 116 regulated genes, 58 genes were significantly upregulated and 58 genes were significantly downregulated (each >2-fold, P < 0.05). Major upregulated genes included suprabasin and myelin basic protein, whereas downregulated genes included BAG2. Several of these genes are known to activate the ERK canonical signal transduction pathway and the process of angiogenesis. We conclude that among other changes, the altered signal transduction molecules involved in high-altitude acclimatization are associated ERK activation and angiogenesis. [ABSTRACT FROM AUTHOR]

We studied single neuron dynamics during anoxic depolarizations, which are often observed in cases of neuronal energy depletion. Anoxic and similar depolarizations play an important role in several pathologies, notably stroke, migraine, and epilepsy. One of the effects of energy depletion was experimentally simulated in slices of rat cortex by blocking the sodium-potassium pumps with ouabain. The membrane voltage of pyramidal cells was measured. Five different kinds of dynamical behavior of the membrane voltage were observed during the resulting depolarizations. Using bifurcation analysis of a single cell model, we show that these voltage dynamics all are responses of the same cell, with normally functioning ion channels, to particular courses of the intra- and extracellular concentrations of sodium and potassium. [ABSTRACT FROM AUTHOR]

Contractions in whole skeletal muscle during hypoxia are known to generate reactive oxygen species (ROS); however, identification of real-time ROS formation within isolated single skeletal muscle fibers has been challenging. Consequently, there is no convincing evidence showing increased ROS production in intact contracting fibers under low PO2 conditions. Therefore, we hypothesized that intracellular ROS generation in single contracting skeletal myofibers increases during low PO2 compared with a value approximating normal resting PO2. Dihydrofluorescein was loaded into single frog (Xenopus) fibers, and fluorescence was used to monitor ROS using confocal microscopy. Myofibers were exposed to two maximal tetanic contractile periods (1 contraction/3 s for 2 min, separated by a 60-min rest period), each consisting of one of the following treatments: high PO2 (30 Torr), low PO2 (3-5 Torr), high PO2 with ebselen (antioxidant), or low PO2 with ebselen. Ebselen (10 μM) was administered before the designated contractile period. ROS formation during low PO2 treatment was greater than during high PO2 treatment, and ebselen decreased ROS generation in both low- and high-PO2 conditions (P < 0.05). ROS accumulated at a faster rate in low vs. high PO2. Force was reduced >30% for each condition except low PO2 with ebselen, which only decreased ~15%. We concluded that single myofibers under low PO2 conditions develop accelerated and more oxidative stress than at PO2 = 30 Torr (normal human resting PO2). Ebselen decreases ROS formation in both low and high PO2, but only mitigates skeletal muscle fatigue during reduced PO2 conditions. [ABSTRACT FROM AUTHOR]

Persons affected by obstructive sleep apnea (OSA) have increased arterial blood pressure and elevated activity in upper airway muscles. Many cardiorespiratory features of OSA have been reproduced in rodents subjected to chronic-intermittent hypoxia (CIH). We previously reported that, following exposure to CIH, rats have increased noradrenergic terminal density in brain stem sensory and motor nuclei and upregulated expression of the excitatory α1-adrenergic receptors in the hypoglossal motor nucleus. This suggested that CIH may enhance central catecholaminergic transmission. We now quantified c-Fos expression in different groups of pontomedullary catecholaminergic neurons as an indirect way of assessing their baseline activity in rats subjected to CIH or sham treatment (7 AM-5 PM daily for 35 days). One day after the last CIH exposure, the rats were gently kept awake for 2.5 h and then were anesthetized and perfused, and their pontomedullary brain sections were subjected to dopamine β-hydroxylase (DBH) and c-Fos immunohistochemistry. DBH-positive cells were counted in the A1/C1, A2/C2, A5, subcoeruleus (sub-C) and A7 groups of catecholaminergic neurons, and the percentages of those expressing c-Fos were determined. We found that fewer DBH cells expressed c-Fos in CIH- than in sham-treated rats in the medulla (significant in the A1 group). In the pons (rostral A5, sub-C, and A7), c-Fos expression did not differ between the CIH- and sham-treated animals. We suggest that, when measured 20 h after the last CIH exposure, catecholaminergic transmission is enhanced through terminal sprouting and receptor upregulation rather than through increased baseline activity in pontomedullary catecholaminergic neurons. [ABSTRACT FROM AUTHOR]

The second member of the transient receptor potential-melastatin channel family (TRPM2) is expressed in the heart and vasculature. TRPM2 channels were expressed in the sarcolemma and transverse tubules of adult left ventricular (LV) myocytes. Cardiac TRPM2 channels were functional since activation with H2O2 resulted in Ca2+ influx that was dependent on extracellular Ca2+, was significantly higher in wild-type (WT) myocytes compared with TRPM2 knockout (KO) myocytes, and inhibited by clotrimazole in WT myocytes. At rest, there were no differences in LV mass, heart rate, fractional shortening, and +dP/dt between WT and KO hearts. At 2-3 days after ischemia-reperfusion (I/R), despite similar areas at risk and infarct sizes, KO hearts had lower fractional shortening and +dP/dt compared with WT hearts. Compared with WT I/R myocytes, expression of the Na+/Ca2+ exchanger (NCX1) and NCX1 current were increased, expression of the _1-subunit of Na+-K+-ATPase and Na+ pump current were decreased, and action potential duration was prolonged in KO I/R myocytes. Post-I/R, intracellular Ca2+ concentration transients and contraction amplitudes were equally depressed in WT and KO myocytes. After 2 h of hypoxia followed by 30 min of reoxygenation, levels of ROS were significantly higher in KO compared with WT LV myocytes. Compared with WT I/R hearts, oxygen radical scavenging enzymes (SODs) and their upstream regulators (forkhead box transcription factors and hypoxia-inducible factor) were lower, whereas NADPH oxidase was higher, in KO I/R hearts. We conclude that TRPM2 channels protected hearts from I/R injury by decreasing generation and enhancing scavenging of ROS, thereby reducing I/Rinduced oxidative stress. [ABSTRACT FROM AUTHOR]

As an immediate consequence of stroke onset, failure of the Na+-K+-ATPase pump evokes a propagating anoxic depolarization (AD) across gray matter. Acute neuronal swelling and dendritic beading arise within seconds in the future ischemic core, imaged as changes in light transmittance (ΔLT). AD is itself not a target for drug-based reduction of stroke injury because it is generated in the 1st min of stroke onset. Peri-infarct depolarizations (PIDs) are milder AD-like events that recur during the hours following AD and contribute to infarct expansion. Inhibiting PIDs with drugs could limit expansion. Two types of drugs, "caines" and σ1-receptor ligands, have been found to inhibit AD onset (and may also oppose PID initiation), yet their underlying actions have not been examined. Imaging ΔLT in the CA1 region simultaneously with whole cell current-clamp recording from CA1 pyramidal neurons reveal that the elevated LT front and onset of the AD are coincident. Either dibucaine or carbetapentane pretreatment significantly delays AD onset without affecting resting membrane potential or neuronal input resistance. Dibucaine decreases excitability by raising spike threshold and decreasing action potential (AP) frequency, whereas carbetapentane eliminates the fast afterhyperpolarization while accentuating the slow afterhyperpolarization to reduce AP frequency. Orthodromic and antidromic APs are eliminated by dibucaine within 15 min but not by carbetapentane. Thus both drugs reduce cortical excitability at the level of the single pyramidal neuron but through strikingly different mechanisms. In vivo, both drugs would likely inhibit recurring PIDs in the expanding penumbra and so potentially could reduce developing neuronal damage over many hours poststroke when PIDs occur. [ABSTRACT FROM AUTHOR]

Evoked potentials recorded from the somatosensory cortex have been shown to be an electrophysiological marker of brain injury in global hypoxic ischemia (HI). The evoked responses in somatosensory neurons carry information pertaining to signal from the ascending pathway in both the subcortical and cortical areas. In this study, origins of the subcortical and cortical signals are explored by decomposing the evoked neuronal activities into short- and long-latency responses (SLR and LLR), respectively. We evaluated the effect of therapeutic hypothermia on SLR and LLR during early recovery from cardiac arrest (CA)-induced HI in a rodent model. Twelve rats were subjected to CA, after which half of them were treated with hypothermia (32-34°C) and the rest were kept at normal temperature (36 -37°C). Evoked neuronal activities from the primary somatosensory cortex, including multiunit activity (MUA) and local field potential (LFP), were continuously recorded during injury and early recovery. Results showed that upon initiation of injury, LLR disappeared first, followed by the disappearance of SLR, and after a period of isoelectric silence SLR reappeared prior to LLR. This suggests that cortical activity, which primarily underlies the LLR, may be more vulnerable to ischemic injury than SLR, which relates to subcortical activity. Hypothermia potentiated the SLR but suppressed the LLR by delaying its recovery after CA (hypothermia: 38.83 ± 5.86 min, normothermia: 23.33 ± 1.15 min; P < 0.05) and attenuating its amplitude, suggesting that hypothermia may selectively downregulate cortical activity as an approach to preserve the cerebral cortex. In summary, our study reveals the vulnerability of the somatosensory neural structures to global HI and the differential effects of hypothermia on these structures. [ABSTRACT FROM AUTHOR]

We expanded our region-based model of water and solute exchanges in the rat outer medulla to incorporate the transport of nitric oxide (NO) and superoxide (O2-) and to examine the impact of NO-O2- interactions on medullary thick ascending limb (mTAL) NaCl reabsorption and oxygen (O2) consumption, under both physiological and pathological conditions. Our results suggest that NaCl transport and the concentrating capacity of the outer medulla are substantially modulated by basal levels of NO and O2-. Moreover, the effect of each solute on NaCl reabsorption cannot be considered in isolation, given the feedback loops resulting from three-way interactions between O2, NO, and O2-. Notwithstanding vasoactive effects, our model predicts that in the absence of O2--mediated stimulation of NaCl active transport, the outer medullary concentrating capacity (evaluated as the collecting duct fluid osmolality at the outer-inner medullary junction) would be ∼40% lower. Conversely, without NO-induced inhibition of NaCl active transport, the outer medullary concentrating capacity would increase by ∼70%, but only if that anaerobic metabolism can provide up to half the maximal energy requirements of the outer medulla. The model suggests that in addition to scavenging NO, O2- modulates NO levels indirectly via its stimulation of mTAL metabolism, leading to reduction of O2 as a substrate for NO. When O2- levels are raised 10-fold, as in hypertensive animals, mTAL NaCl reabsorption is significantly enhanced, even as the inefficient use of O2 exacerbates hypoxia in the outer medulla. Conversely, an increase in tubular and vascular flows is predicted to substantially reduce mTAL NaCl reabsorption. In conclusion, our model suggests that the complex interactions between NO, O2-, and O2 significantly impact the O2 balance and NaCl reabsorption in the outer medulla. [ABSTRACT FROM AUTHOR]

N-methyl-d-aspartate receptors (NMDARs) are Ca2+-permeable, ligand-gated, nonselective cation channels that function as neuronal synaptic receptors but which are also expressed in multiple peripheral tissues. Here, we show for the first time that NMDAR subunits NR3a and NR3b are highly expressed in the neonatal kidney and that there is continued expression of NR3a in the renal medulla and papilla of the adult mouse. NR3a was also expressed in mIMCD-3 cells, where it was found that hypoxia and hypertonicity upregulated NR3a expression. Using short-hairpin (sh) RNA-based knockdown, a stable inner medullary collecting duct (IMCD) cell line was established that had ∼80% decrease in NR3a. Knockdown cells exhibited an increased basal intracellular calcium concentration, reduced cell proliferation, and increased cell death. In addition, NR3a knockdown cells exhibited reduced water transport in response to the addition of vasopressin, suggesting an alteration in aquaporin-2 (AQP2) expression/function. Consistent with this notion, we demonstrate decreased surface expression of glycosylated AQP2 in IMCD cells transfected with NR3a shRNA. To determine whether this also occurred in vivo, we compared AQP2 levels in wild-type vs. in NR3a-/- mice. Total AQP2 protein levels in the outer and inner medulla were significantly reduced in knockout mice compared with control mice. Finally, NR3a-/- mice showed a significant delay in their ability to increase urine osmolality during water restriction. Thus NR3a may play a renoprotective role in collecting duct cells. Therefore, under conditions that are associated with high vasopressin levels, NR3a, by maintaining low intracellular calcium levels, protects the function of the principal cells to reabsorb water and thereby increase medullary osmolality. [ABSTRACT FROM AUTHOR]

To understand how arterial-to-venous (AV) oxygen shunting influences kidney oxygenation, a mathematical model of oxygen transport in the renal cortex was created. The model consists of a multiscale hierarchy of 11 countercurrent systems representing the various branch levels of the cortical vasculature. At each level, equations describing the reactive- advection-diffusion of oxygen are solved. Factors critical in renal oxygen transport incorporated into the model include the parallel geometry of arteries and veins and their respective sizes, variation in blood velocity in each vessel, oxygen transport (along the vessels, between the vessels and between vessel and parenchyma), nonlinear binding of oxygen to hemoglobin, and the consumption of oxygen by renal tissue. The model is calibrated using published measurements of cortical vascular geometry and microvascular Po2. The model predicts that AV oxygen shunting is quantitatively significant and estimates how much kidney V̇o2 must change, in the face of altered renal blood flow, to maintain cortical tissue Po2 at a stable level. It is demonstrated that oxygen shunting increases as renal V̇o2 or arterial Po2 increases. Oxygen shunting also increases as renal blood flow is reduced within the physiological range or during mild hemodilution. In severe ischemia or anemia, or when kidney V̇o2 increases, AV oxygen shunting in proximal vascular elements may reduce the oxygen content of blood destined for the medullary circulation, thereby exacerbating the development of tissue hypoxia. That is, cortical ischemia could cause medullary hypoxia even when medullary perfusion is maintained. Cortical AV oxygen shunting limits the change in oxygen delivery to cortical tissue and stabilizes tissue Po2 when arterial Po2 changes, but renders the cortex and perhaps also the medulla susceptible to hypoxia when oxygen delivery falls or consumption increases. [ABSTRACT FROM AUTHOR]

Cyst expansion in polycystic kidney disease (PKD) results in localized hypoxia in the kidney that may activate hypoxia-inducible factor-1α (HIF-1α). HIF-1α and autophagy, a form of programmed cell repair, are induced by hypoxia. The purposes were to determine HIF-1α expression and autophagy in rat and mouse models of PKD. HIF-1α was detected by electrochemiluminescence. Autophagy was visualized by electron microscopy (EM). LC3 and beclin-1, markers of autophagy, were detected by immunoblotting. Eight-week-old male heterozygous (Cy/+) and 4-wk-old homozygous (Cy/Cy) Han:SPRD rats, 4-wk-old cpk mice, and 112-day-old Pkd2WS25/- mice with a mutation in the Pkd2 gene were studied. HIF-1α was significantly increased in massive Cy/Cy and cpk kidneys and not smaller Cy/+ and Pkd2WS25/- kidneys. On EM, features of autophagy were seen in wild-type (+/+), Cy/+, and cpk kidneys: autophagosomes, mitophagy, and autolysosomes. Specifically, autophagosomes were found on EM in the tubular cells lining the cysts in cpk mice. The increase in LC3-II, a marker of autophagosome production and beclin, a regulator of autophagy, in Cy/Cy and cpk kidneys, followed the same pattern of increase as HIF-1α. To determine the role of HIF-1α in cyst formation and/or growth, Cy/+ rats, Cy/Cy rats, and cpk mice were treated with the HIF-1α inhibitor 2-methoxyestradiol (2ME2). 2ME2 had no significant effect on kidney volume or cyst volume density. In summary, HIF-1α is highly expressed in the late stages of PKD and is associated with an increase in LC3-II and beclin-1. The first demonstration of autophagosomes in PKD kidneys is reported. Inhibition of HIF-1α did not have a therapeutic effect. [ABSTRACT FROM AUTHOR]

Apoptosis plays a significant role in maladaptive remodeling and ventricular dysfunction following ischemia-reperfusion injury. There is a critical need for novel approaches to inhibit apoptotic cell death following reperfusion, as this loss of cardiac myocytes can progressively lead to heart failure. We investigated the ability and signaling mechanisms of a high-molecular-weight polyethylene glycol-based copolymer, PEG 15-20, to protect cardiac myocytes from hypoxia-reoxygenation (H-R)-induced cell death and its efficacy in preserving ventricular function following extended hypothermic ischemia and warm reperfusion as relevant to cardiac transplantation. Pretreatment of neonatal rat ventricular myocytes with a 5% PEG solution led to a threefold decline in apoptosis after H-R relative to untreated controls. There was a similar decline in caspase-3 activity in conjunction with inhibition of cytochrome c release from the inner mitochondrial membrane. Treatment with PEG also reduced reactive oxygen species production after H-R, and sarcolemmal lipid-raft architecture was preserved, consistent with membrane stabilization. Cell survival signaling was upregulated after H-R with PEG, as demonstrated by increased phosphorylation of Akt, GSK-3β, and ERK1/2. There was also maintenance of cardiac myocyte β-adrenergic signaling, which is critical for myocardial function. PEG 15-20 was very effective in preserving left ventricular function following prolonged hypothermic ischemia and warm reperfusion. PEG 15-20 has a potent protective antiapoptotic effect in cardiac myocytes exposed to H-R injury and may represent a novel therapeutic strategy to decrease myocardial cell death and ventricular dysfunction at the time of reperfusion during acute coronary syndrome or following prolonged donor heart preservation. [ABSTRACT FROM AUTHOR]

The matching of energy supply and demand under hypoxic conditions is critical for sustaining myocardial function. Numerous reports indicate that basal energy requirements and ion handling may differ between the ventricles. We hypothesized that ventricular response to hypoxia shows interventricular differences caused by the heterogeneity in glucose metabolism and expression and activity of ion transporters. Thus we assessed glucose utilization rate, ATP, sodium and potassium concentrations, Na, K-ATPase activity, and tissue reduced:oxidized glutathione (GSH/GSSG) content in the right and left ventricles before and after the exposure of either the whole animals or isolated blood-perfused hearts to hypoxia. The hypoxia-induced boost in glucose utilization was more pronounced in the left ventricle compared with the right one. ATP levels in the right ventricle of hypoxic heart were lower than those in the left ventricle. Left ventricular sodium content was higher, and hydrolytic Na, K-ATPase activity was reduced compared with the right ventricle. Administration of the Na, K-ATPase blocker ouabain caused rapid increase in the right ventricular Na+ and elimination of the interventricular Na+ gradients. Exposure of the hearts to hypoxia made the interventricular heterogeneity in the Na+ distribution even more pronounced. Furthermore, systemic hypoxia caused oxidative stress that was more pronounced in the right ventricle as revealed by GSH/GSSG ratios. On the basis of these findings, we suggest that the right ventricle is more prone to hypoxic damage, as it is less efficient in recruiting glucose as an alternative fuel and is particularly dependent on the efficient Na, K-ATPase function. [ABSTRACT FROM AUTHOR]

During pulmonary edema, the alveolar space is exposed to a hypoxic environment. The integrity of the alveolar epithelial barrier is required for the reabsorption of alveolar fluid. Tight junctions (TJ) maintain the integrity of this barrier. We set out to determine whether hypoxia creates a dysfunctional alveolar epithelial barrier, evidenced by an increase in transepithelial electrical conductance (Gt), due to a decrease in the abundance of TJ proteins at the plasma membrane. Alveolar epithelial cells (AEC) exposed to mild hypoxia (Po2 = 50 mmHg) for 30 and 60 min decreased occludin abundance at the plasma membrane and significantly increased Gt. Other cell adhesion molecules such as E-cadherin and claudins were not affected by hypoxia. AEC exposed to hypoxia increased superoxide, but not hydrogen peroxide (H2O2). Overexpression of superoxide dismutase 1 (SOD1) but not SOD2 prevented the hypoxia-induced Gt increase and occludin reduction in AEC. Also, overexpression of catalase had a similar effect as SOD1, despite not detecting any increase in H2O2 during hypoxia. Blocking PKC-ζ and protein phosphatase 2A (PP2A) prevented the hypoxia-induced occludin reduction at the plasma membrane and increase in Gt. In summary, we show that superoxide, PKC-ζ, and PP2A are involved in the hypoxia-induced increase in Gt and occludin reduction at the plasma membrane in AEC. [ABSTRACT FROM AUTHOR]

Whole brain radiation therapy (WBRT) leads to cognitive impairment in 40-50% of brain tumor survivors following treatment. Although the etiology of cognitive deficits post-WBRT remains unclear, vascular rarefaction appears to be an important component of these impairments. In this study, we assessed the effects of WBRT on the cerebrovasculature and the effects of systemic hypoxia as a potential mechanism to reverse the microvascular rarefaction. Transgenic mice expressing green fluorescent protein driven by the Acta2 (smooth muscle actin) promoter for blood vessel visualization were randomly assigned to control or radiated groups. systemic hypoxia. Our results indicate a potential shift in sensitivity to angiogenic stimuli and/or the existence of an independent pathway of regulating cerebral microvasculature. [ABSTRACT FROM AUTHOR]

The PO2 within the kidney changes dramatically from cortex to medulla. The present experiments examined the effect of changing PO2 on epithelial Na channel (ENaC)-mediated Na transport in the collecting duct using the mpkCCD-c14 cell line. Decreasing ambient O2 concentration from 20 to 8% decreased ENaC activity by 40%; increasing O2 content to 40% increased ENaC activity by 50%. The O2 effect required several hours to develop and was not mimicked by the acid pH that developed in monolayers incubated in low-O2 medium. Corticosteroids increased ENaC activity at each O2 concentration; there was no interaction. The pathways for O2 and steroid regulation of ENaC are different since O2 did not substantially affect Sgk1, α-ENaC, Gilz, or Usp2-45 mRNA levels, genes involved in steroid-mediated ENaC regulation. The regulation of ENaC activity by these levels of O2 appears not to be mediated by changes in hypoxia-inducible factor-1α or -2α activity or a change in AMP kinase activity. Changes in O2 concentration had minimal effect on α- or γ-ENaC mRNA and protein levels; there were moderate effects on β-ENaC levels. However, 40% O2 induced substantially greater total β- and γ-ENaC on the apical surface compared with 8% O2; both subunits demonstrated a greater increase in the mature forms. The α-ENaC subunit was difficult to detect on the apical surface, perhaps because our antibodies do not recognize the major mature form. These results identify a mechanism of ENaC regulation that may be important in different regions of the kidney and in responses to changes in dietary NaCl. [ABSTRACT FROM AUTHOR]

Hypoxia often causes body water deficits (hypohydration, HYPO); however, the effects of HYPO on aerobic exercise performance and prevalence of acute mountain sickness (AMS) at high altitude (ALT) have not been reported. We hypothesized that 1) HYPO and ALT would each degrade aerobic performance relative to sea level (SL)-euhydrated (EUH) conditions, and combining HYPO and ALT would further degrade performance more than one stressor alone; and 2) HYPO would increase the prevalence and severity of AMS symptoms. Seven lowlander men (25 ± 7 yr old; 82 ± 11 kg; mean ± SD) completed four separate experimental trials. Trials were 1) SL-EUH, 2) SL-HYPO, 3) ALT-EUH, and 4) ALT-HYPO. In HYPO, subjects were dehydrated by 4% of body mass. Subjects maintained hydration status overnight and the following morning entered a hypobaric chamber (at SL or 3,048 m, 27°(2) where they completed 30 min of submaximal exercise immediately followed by a 30-min performance time trial (TF). AMS was measured with the Environmental Symptoms Questionnaire-Cerebral Score (AMS-C) and the Lake Louise Scoring System (LLS). The percent change in TT performance, relative to SL-EUH, was -19 ± 12% (334 ± 64 to 278 ± 87 kJ), -11 ± 10% (334 ± 64 to 293 ± 33 kJ), and -34 ± 22% (334 ± 64 to 227 ± 95 kJ). for SL-HYPO, ALT-EUH, and ALT-HYPO, respectively. AMS symptom prevalence was 2/7 subjects at ALT-EUH for AMS-C and LLS and 5/7 and 4/7 at ALT-HYPO for AMS-C and LLS, respectively. The AMS-C symptom severity score (AMS-C score) tended to increase from ALT-EUH to ALT-HYPO but was not significant (P = 0.07). In conclusion, hypohydration at 3,048 m 1) degrades aerobic performance in an additive manner with that induced by ALT; and 2) did not appear to increase the prevalence/ severity of AMS symptoms. [ABSTRACT FROM AUTHOR]

Supraspinal fatigue, defined as an exercise-induced decline in force caused by suboptimal output from the motor cortex, accounts for over one-quarter of the force loss after fatiguing contractions of the knee extensors in normoxia. We tested the hypothesis that the relative contribution of supraspinal fatigue would be elevated with increasing severities of acute hypoxia. On separate days, 11 healthy men performed sets of intermittent, isometric, quadriceps contractions at 60% maximal voluntary contraction to task failure in normoxia (inspired O2 fraction/arterial O2 saturation = 0.21/98%), mild hypoxia (0.16/ 93%), moderate hypoxia (0.13/85%), and severe hypoxia (0.10/74%). Electrical stimulation of the femoral nerve was performed to assess neuromuscular transmission and contractile properties of muscle fibers. Transcranial magnetic stimulation was delivered to the motor cortex to quantify corticospinal excitability and voluntary activation. After 10 rain of breathing the test gas, neuromuscular function and cortical voluntary activation prefatigue were unaffected in any condition. The fatigue protocol resulted in ~30% declines in maximal voluntary contraction force in all conditions, despite differences in time-to-task failure (24.7 min in normoxia vs. 15.9 min in severe hypoxia, P < 0.05). Potentiated quadriceps twitch force declined in all conditions, but the decline in severe hypoxia was less than that in normoxia (P < 0.05). Cortical voluntary activation also declined in all conditions, but the deficit in severe hypoxia exceeded that in normoxia (P < 0.05). The additional central fatigue in severe hypoxia was not due to altered corticospinal excitability, as electromyographic responses to transcranial magnetic stimulation were unchanged. Results indicate that peripheral mechanisms of fatigue contribute relatively more to the reduction in force-generating capacity of the knee extensors following submaximal intermittent isometric contractions in normoxia and mild to moderate hypoxia, whereas supraspinal fatigue plays a greater role in severe hypoxia. [ABSTRACT FROM AUTHOR]

Arousal is an important survival mechanism when infants are confronted with hypoxia during sleep. Many sudden infant death syndrome (SIDS) infants are exposed to repeated episodes of hypoxia before death and have impaired arousal mechanisms. We hypothesized that repeated exposures to hypoxia would cause a progressive blunting of arousal, and that a reversal of this process would occur if the hypoxia was terminated at the time of arousal. P5 (postnatal age of 5 days), P15, and P25 rat pups were exposed to either eight trials of hypoxia (3 min 5% O2 alternating with room air) (group A), or three hypoxia trials as in group A, followed by five trials in which hypoxia was terminated at arousal (group B). In both groups A and B, latency increased over the first four trials of hypoxia, but reversed in group B animals during trials 5-8. Progressive arousal blunting was more pronounced in the older pups. The effects of intermittent hypoxia on heart rate also depended on age. In the older pups, heart rate increased with each hypoxia exposure. In the P5 pups, however, heart rate decreased during hypoxia and did not return to baseline between exposures, resulting in a progressive fall of baseline values over successive hypoxia exposures. In the group B animals, heart rate changes during trials 1-4 also reversed during trials 5-8. We conclude that exposure to repeated episodes of hypoxia can cause progressive blunting of arousal, which is reversible by altering the exposure times to hypoxia and the period of recovery between hypoxia exposures. [ABSTRACT FROM AUTHOR]

Although many effects of both acute and chronic hypoxia on the circulation are well characterized, the distribution and regulation of blood flow (BF) heterogeneity in skeletal muscle during systemic hypoxia is not well understood in humans. We measured muscle BF within the thigh muscles of nine healthy young men using positron emission tomography during one-leg dynamic knee extension exercise in normoxia and moderate physiological systemic hypoxia (14% O2 corresponding to ∼3,400 m of altitude) without and with local adenosine receptor inhibition with femoral artery infusion of aminophylline. Systemic hypoxia reduced oxygen extraction of the limb but increased muscle BF, and this flow increment was confined solely to the exercising quadriceps femoris muscle. Exercising muscle BF heterogeneity was reduced from rest (P = 0.055) but was not affected by hypoxia. Adenosine receptor inhibition had no effect on capillary BF during exercise in either normoxia or hypoxia. Finally, one-leg exercise increased muscle BF heterogeneity both in the resting posterior hamstring part of the exercising leg and in the resting contralateral leg, whereas mean BF was unchanged. In conclusion, the results show that increased BF during one-leg exercise in moderate hypoxia is confined only to the contracting muscles, and the working muscle hyperemia appears not to be directly mediated by adenosine. Increased flow heterogeneity in noncontracting muscles likely reflects sympathetic nervous constraints to curtail BF increments in areas other than working skeletal muscles, but this effect is not potentiated in moderate systemic hypoxia during small muscle mass exercise. [ABSTRACT FROM AUTHOR]

Babies are frequently exposed to cerebral hypoxia and ischemia (H/I) during the perinatal period as a result of stroke, problems with delivery, or postdelivery respiratory management. The sole approved treatment for acute stroke is tissue type plasminogen activator. H/I impairs pial artery dilation (PAD) induced by hypercapnia and hypotension, the impairment aggravated by type plasminogen activator and attenuated by the plasminogen activator inhibitor-1-derived peptide EEIIMD. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, ERK, p38, and JNK, is upregulated after H/I and ERK contribute to impaired cerebrovasodilation. This study determined the roles of p38 and JNK MAPK in the impairment of dilation post-H/I in pigs equipped with a closed cranial window and the relationship between alterations in MAPK isoforms and EEIIMD-mediated cerebrovascular protection. Cerebrospinal fluid-phosphorylated (activated) p38 MAPK, but not JNK MAPK, was increased after H/I, an effect potentiated by intravenous EEIIMD administered 1 h postinjury. PAD in response to hypercapnia and hypotension was blunted by H/I, but dilation was maintained by EEIIMD. PAD was further impaired by the p38 antagonist SB-203580 but unchanged by the JNK antagonist SP-600125. Isoproterenol-induced PAD was unchanged by H/I, EEIIMD, SB-203580, and SP-600125. These data indicate that postinjury treatment with EEIIMD attenuated impaired cerebrovasodilation post-H/I by upregulating p38 but not JNK. These data suggest that plasminogen activator inhibitor-1-based peptides and other approaches to upregulate p38 may offer a novel approach to increase the benefit-to-risk ratio of thrombolytic therapy for diverse central nervous system disorders associated with H/I. [ABSTRACT FROM AUTHOR]

Effects of hypoxia on cerebral circulation are important for occupational, high-altitude, and aviation medicine. Increased risk of fainting might be attributable to altered cerebral circulation by hypoxia. Dynamic cerebral autoreg ulation is reportedly impaired immediately by mild hypoxia. How ever, continuous exposure to hypoxia causes hyperventilation, result ing in hypocapnia. This hypocapnia is hypothesized to restore im paired dynamic cerebral autoregulation with reduced steady-state cerebral blood flow (CBF). However, no studies have examined hourly changes in alterations of dynamic cerebral autoregulation and steady-state CBF during sustained hypoxia. We therefore examined cerebral circulation during 5-h exposure to 15% O2 hypoxia and 21% O2 in 13 healthy volunteers in a sitting position. Waveforms of blood pressure and CBF velocity in the middle cerebral artery were mea sured using finger plethysmography and transcranial Doppler ultra sonography. Dynamic cerebral autoregulation was assessed by spec tral and transfer function analysis. As expected, steady-state CBF velocity decreased significantly from 2 to 5 h of hypoxia, accompa nying 2 to 3-Ton decreases in end-tidal CO2 (ETCO2). Furthermore, transfer function gain and coherence in the very-low-frequency range increased significantly at the beginning of hypoxia, indicating im paired dynamic cerebral autoregulation. However, contrary to the proposed hypothesis, indexes of dynamic cerebral autoregulation showed no significant restoration despite ETCO2 reductions, resulting in persistent higher values of very-low-frequency power of CBF velocity variability during hypoxia (214 ± 40% at 5 h of hypoxia vs. control) without significant increases in blood pressure variability. These results suggest that sustained mild hypoxia reduces steady-state CBF and continuously impairs dynamic cerebral autoregulation, im plying an increased risk of shortage of oxygen supply to the brain. [ABSTRACT FROM AUTHOR]

Acute mountain sickness (AMS) develops within a few hours after arrival at high altitude and includes headache, anorexia, nausea, vomiting, and malaise. This afflicts 15-25% of the general tourist population at moderate altitudes. High-altitude cerebral edema(HACE) is considered to be the end stage of severe AMS and has been suggested to be a vasogenic edema, raising the possibility that acute hypoxia may increase blood-brain barrier (BBB) permeability. At present, there are no good small-animal models to study this syndrome. We hypothesize 1) that acute hypoxia can damage the BBB and 2) that rat can be used as a model to study hypoxia-induced changes in BBB permeability, especially if hypoxia-induced hypothermia could be minimized with high ambient temperature (HAT). Male Wistar rats were exposed to 1, 2, and 7 days of hypobaric hypoxia (equivalent to 0.5 atm), and changes in the temperature and BBB permeability were studied. The extravasation of endogenous immunoglobulin G, a large molecule, did not increase during room temperature hypoxia but did increase when hypoxia was combined with HAT. Hypoxia caused a significant increase in the leakage of sodium fluorescein (mol wt 376 Da). The expression of endothelial barrier antigen (EBA), a protein associated with the BBB, was reduced to 50% between 24 and 48 h after exposure to hypoxia, and the loss was exacerbated by HAT. The values almost returned to control levels by 7 days, showing adaptation to hypoxia. Hypoxic rats exhibited sodium fluorescein leakage mainly in focal areas in the brain parenchyma. In conclusion, it is possible to have transient BBB damage through exposure to acute hypoxia, and this damage is exacerbated by increasing body temperature to more of a normothermic value. [ABSTRACT FROM AUTHOR]

The contribution of sympathetic nerves arising from the superior cervical ganglia (SCG) toward the growth and function of cerebral blood vessels is pertinent throughout maturation as well as in response to cardiovascular stress imposed by high-altitude long-term hypoxia (LTH). The function of SCG sympathetic neurons is dependent on intracellular Ca2+ concentration ([Ca2+]i) signaling, which is strongly influenced by a process known as Ca2+-induced Ca2+ release (CICR) from the smooth endoplasmic reticulum (SER). In this study, we used the sheep SCG neuronal model to test the hypotheses that maturation decreases CICR and high-altitude LTH depresses CICR in fetal SCG neurons but not in those of the adult. We found that the contribution of CICR to electric field stimulation (EFS)-evoked [Ca2+]i transients was greatest in SCG cells from normoxic fetuses and was abolished by LTH. The decline in CICR was associated with a reduction in sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) function in fetal SCG cells during LTH, reducing SER Ca2+ levels below the threshold needed for the coupling of Ca2+ influx and CICR. With respect to the maturation from the fetus to adult, the decrease in CICR may reflect both a reduction in the levels of ryanodine receptor isoforms 2 and 3 and SERCA function. In response to LTH and in contrast to the fetus, CICR function in adult SCG cells is maintained and may reflect alterations in other mechanisms that modulate the CICR process. As CICR is instrumental in the function of sympathetic neurons within the cerebrovasculature, the loss of this signaling mechanism in the fetus may have consequences for the adaptation to LTH in terms of fetal susceptibility to vascular insults. [ABSTRACT FROM AUTHOR]

We investigated the effect of acute hypoxia (AH) on dynamic cerebral autoregulation (CA) using two independent assessment techniques to clarify previous, conflicting reports. Twelve healthy volunteers (6 men, 6 women) performed six classic leg cuff tests, three breathing normoxic (FlO2 = 0.21) and three breathing hypoxic (Fl02 = 0.12) gas, using a single blinded, Latin squares design with 5-mm washout between trials. Continuous measurements of middle cerebral artery blood flow velocity (CBFv; DWL MultiDop X2) and radial artery blood pressure (ABP; Cohn 7000) were recorded in the supine position during a single experimental session. Autoregulation index (ARI) scores were calculated using the model of Tiecks et al. (Tiecks FP, Lam AM, Aashid R, Newell DW. Stroke 26: 1014-1019, 1995) from ABP and CBFv changes following rapid cuff deflation (cuff ARI) and from ABP to CBFv transfer function, impulse, and step responses (TFA ARI) obtained during a 4-mm period prior to cuff inflation. A new measure of %CBFv recovery 4 s after peak impulse was also derived from TFA. AH reduced cuff ARI (5.65 ± 0.70 to 5.01 ± 0.96, P = 0.04), TFA ARI (4.37 ± 0.76 to 3.73 ± 0.71, P 0.04), and %Recovery (62.2 ± 10.9% to 50.8 ± 9.9%, P = 0.03). Slight differences between TFA and cuff ARI values may be attributed to heightened sympathetic activity during cuff tests as well as differential sensitivity to lowand high-frequency components of CA. Together, results provide consistent evidence that CA is impaired with AH. In addition, these findings demonstrate the potential utility of TFA ARI and %Recovery scores for future CA investigations. [ABSTRACT FROM AUTHOR]

Even though renal hypoxia is believed to play a pivotal role in the development of acute kidney injury, no study has specifically addressed the alterations in renal oxygenation in the early onset of renal ischemia-reperfusion (I/R). Renal oxygenation depends on a balance between oxygen supply and consumption, with the nitric oxide (NO) as a major regulator of microvascular oxygen supply and oxygen consumption. The aim of this study was to investigate whether I/R induces inducible NO synthase (iNOS)-dependent early changes in renal oxygenation and the potential benefit of iNOS inhibitors on such alterations. Anesthetized Sprague-Dawley rats underwent a 30-min suprarenal aortic clamping with or without either the nonselective NO synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) or the selective iNOS inhibitor L-N6-(1-iminoethyl)lysine hydrochloride (L- NIL). Cortical (CμPo2) and outer medullary (MμPo2) microvascular oxygen pressure (μPo2), renal oxygen delivery (DO2ren), renal oxygen consumption (VO2ren)), and renal oxygen extraction (O2ER) were measured by oxygen-dependent quenching phosphorescence techniques throughout 2 h of reperfusion. During reperfusion renal arterial resistance and oxygen shunting increased, whereas renal blood flow, CμPo2, and MμPo2 (-70, -42, and -42%, respectively, P < 0.05), VO2ren, and DO2ren (-70%, P < 0.0001, and -28%, P < 0.05) dropped. Whereas L-NAME further decreased DO2ren, VO2ren, CμPO2, and MμPo2 and deteriorated renal function, L-NIL partially prevented the drop of DO2ren and μPo2, increased O2ER, restored VO2ren and metabolic efficiency, and prevented deterioration of renal function. Our results demonstrate that renal I/R induces early iNOS-dependent microvascular hypoxia in disrupting the balance between microvascular oxygen supply and VO2ren, whereas endothehial NO synthase activity is compulsory for the maintenance of this balance. L-NIL can prevent ischemic-induced renal microvascular hypoxia. [ABSTRACT FROM AUTHOR]

Glutamatergic synaptic currents elicited in second-order neurons in the nucleus of the solitary tract (nTS) by activation of chemosensory and other visceral afferent fibers are severely reduced following 10 days of chronic intermittent hypoxia (CIH). The mechanism by which this occurs is unknown. A strong candidate for producing the inhibition is dopamine, which is also released from the presynaptic terminals and which we have shown exerts a tonic presynaptic inhibition on glutamate release. We postulated that tonic activation of the D2 receptors inhibits presynaptic calcium currents to reduce transmitter release and that in CIH this occurs in conjunction with an increase in the dopamine inhibitory response due to the increase in presynaptic D2 receptors or an increase in dopamine release further suppressing the evoked excitatory postsynaptic current (eEPSC). Thus we predicted that blockade of the D2 receptors would return the EPSC to values of animals maintained under normoxic conditions. We found that dopamine and quinpirole, the selective D2-like agonist, inhibit calcium currents via the D2 receptors by acting on the N-type calcium channel in presynaptic neurons and their nTS central terminals. However, in brain slice studies from CIH animals, although the D2 antagonist sulpiride increased the CIH-reduced amplitude of synaptic currents, EPSCs were not restored to normal levels. This indicates that while the dopamine inhibitory effect remains intact in CIH, most of the reduction in the eEPSC amplitude occurs via alternative mechanisms. [ABSTRACT FROM AUTHOR]

Spreading depression (SD) resembles a concerted, massive neuronal/glial depolarization propagating within the gray matter. Being associated with cerebropathology, such as cerebral ischemia or hemorrhage, epileptic seizures, and migraine, it is well studied in cortex and hippocampus. We have now analyzed the susceptibility of rat brain stem to hypoxia-induced spreading depression-like depolarization (HSD), which could critically interfere with cardiorespiratory control. In rat brain stem slices, severe hypoxia (oxygen withdrawal) triggered HSD within minutes. The sudden extracellular DC potential shift of approximately –20 mV showed the typical profile known from other brain regions and was accompanied by an intrinsic optical signal (IOS). Spatiotemporal IOS analysis revealed that in infant brain stem, HSD was preferably ignited within the spinal trigeminal nucleus and then mostly spread out medially, invading the hypoglossal nucleus, the nucleus of the solitary tract (NTS), and the ventral respiratory group (VRG). The neuronal hypoxic depolarizations underlying the generation of HSD were massive, but incomplete. The propagation velocity of HSD and the associated extracellular K+rise were also less marked than in other brain regions. In adult brain stem, HSD was mostly confined to the NTS and its occurrence was facilitated by hypotonic solutions, but not by glial poisoning or block of GABAergic and glycinergic synapses. In conclusion, brain stem tissue reliably generates propagating HSD episodes, which may be of interest for basilar-type migraine and brain stem infarcts. The preferred occurrence of HSD in the infant brain stem and its propagation into the VRG may be of importance for neonatal brain stem pathology such as sudden infant death syndrome. [ABSTRACT FROM AUTHOR]

Decreased cerebral blood flow (CBF) has been observed following the resuscitation from neonatal hypoxic-ischemic injury, but its mechanism is not known. We address the hypothesis that reduced CBF is due to a change in nitric oxide (NO) and superoxide anion O2- balance secondary to endothelial NO synthase (eNOS) uncoupling with vascular injury. Wistar rats (7 day old) were subjected to cerebral hypoxia-ischemia by unilateral carotid occlusion under isoflurane anesthesia followed by hypoxia with hyperoxic or normoxic resuscitation. Expired CO2 was determined during the period of hyperoxic or normoxic resuscitation. Laser-Doppler flowmetry was used with isoflurane anesthesia to monitor CBF, and cerebral perivascular NO and O2- were determined using fluorescent dyes with fluorescence microscopy. The effect of tetrahydrobiopterin supplementation on each of these measurements and the effect of apocynin and Nω-nitro-L-arginine methyl ester (L-NAME) administration on NO and O2- were determined. As a result, CBF in the ischemic cortex declined following the onset of resuscitation with 100% O2 (hyperoxic resuscitation) but not room air (normoxic resuscitation). Expired CO2 was decreased at the onset of resuscitation, but recovery was the same in normoxic and hyperoxic resuscitated groups. Perivascular NO-induced fluorescence intensity declined, and Of-induced fluorescence increased in the ischemic cortex after hyperoxic resuscitation up to 24 h postischemia. L-NAME treatment reduced O2- relative to the nonischemic cortex. Apocynin treatment increased NO and reduced O2- relative to the nonischemic cortex. The administration of tetrahydrobiopterin following the injury increased perivascular NO, reduced perivascular O2-, and increased CBF during hyperoxic resuscitation. These results demonstrate that reduced CBF follows hyperoxic resuscitation but not normoxic resuscitation after neonatal hypoxic-ischemic injury, accompanied by a reduction in perivascular production of NO and an increase in O2-. The finding that tetrahydrobiopterin, apocynin, and L-NAME normalized radical production suggests that the uncoupling of perivascular NOS, probably eNOS, due to acquired relative tetrahydrobiopterin deficiency occurs after neonatal hypoxic-ischemic brain injury. It appears that both NOS uncoupling and the activation of NADPH oxidase participate in the changes of reactive oxygen concentrations seen in cerebral hypoxic-ischemic injury. [ABSTRACT FROM AUTHOR]

Kan W-H, Hsu J-T, Schwacha MG, Choudhry MA, Raju R, Bland K!, Chaudry Ill. Selective inhibition of iNOS attenuates trauma-hemorrhage/msuscitation-induced hepatic injuiy. J Appi Physiol 105: 1076-1082, 2008. First published July 17,2008; doi: 10.1 l52ljapplphysiol.90495.2008.Although trauma-hemorrhage produces tissue hypoxia, systemic inflammatory response and organ dysfunction, the mechanisms responsible for these alterations are not clear. Using a potent selective inducible nitric oxide (NO) synthase inhibitor, N-[3-(aminomethyl) benzyl]acetamidine (1400W), and a nonselective NO synthase inhibitor, M3-nitro-L-arginine methyl ester (L-NAME), we investigated whether inducible NO synthase plays any role in producing hepatic injury, inflammation, and changes of protein expression following trauma-hemorrhage. To investigate this, male Sprague-Dawley rats were subjected to midline laparotomy and hemorrhagic shock (mean blood pressure 35-40 mmHg for ∼90 mm) followed by fluid resuscitation. Animals were treated with either vehicle (DMSO) or 1400W (10 mg/kg body wt ip), or L-NAME (30 mg/kg iv), 30 mm before resuscitation and killed 2 h after resuscitation. Trauma-hemorrhage/ resuscitation induced a marked hypotension and increase in markers of hepatic injury (i.e., plasma a-glutathione S-transferase, tissue myeloperoxidase activity, and nitrotyrosine formation). Hepatic expression of iNOS, hypoxia-inducible factor-1α, ICAM1, IL-6, TNF-a, and neutrophil chemoattractant (cytokine-induced neutrophil chemoattractant1 and macrophage inflammatory protein-2) protein levels were also markedly increased following trauma-hemorrhage/ resuscitation. Administration of the iNOS inhibitor 1400W significantly attenuated hypotension and expression of these mediators of hepatic injury induced by trauma-hemorrhage/resuscitation. However, administration of ʟ-NAME could not attenuate hepatic dysfunction and tissue injury mediated by trauma-hemorrhage, although it improved mean blood pressure as did 1400W. These results indicate that increased expression of iNOS following trauma-hemorrhage plays an important role in the induction of hepatic damage under such conditions. [ABSTRACT FROM AUTHOR]

Ischemia-reperfusion injury is one of the central nonimmunologic processes involved in renal allograft dysfunction. Kidneys from non-heart beating donors (NHBD) exhibit higher rates of delayed graft function (DGF) than those from other donors. Primary nonfunction and DGF are the main barriers to the use of kidneys from NHBD. Using a pig model of NHBD transplantation, we studied the effect of FR167653 (a p38 MAP kinase inhibitor) on the recovery and reparation of kidneys exposed to both warm (WI: 1 h) and cold ischemia (24 h). Our results demonstrate that the addition of FR167653 increases the kinetics of proximal tubule cell regeneration after 60 mm of WI. Hypoxia-inducible factor and vascular endothelial growth factor expression was also more important in FR167653-treated kidneys compared with those in nontreated groups. Also, expression of peripheral-type benzodiazepine receptor, involved in tissue repair, was increased in the FR167653-treated groups. At 3 mo, the protective effects of FR167653 were accompanied by a reduction of long-term inflammation process and tubulointerstitial fibrosis development associated with a limitation of ischemia-induced remodeling. This study suggests that such treatment may be useful in protocols aimed at improving the quality of renal transplants from NHBD. In addition, the beneficial role of FR167653 in limiting early injury is associated with secondary reduction in development of tubular atrophy and interstitial fibrosis which are together the hallmark of failing renal transplants. The more efficient effect was observed when FR167653 was added in combination before WI, during cold storage and reperfusion. [ABSTRACT FROM AUTHOR]

Na+ cotransporters have a substantial role in neuronal damage during brain hypoxia. We proposed these cotransporters have beneficial roles in oxygen-sensing mechanisms that increase periarteriolar nitric oxide (NO) concentration ([NO]) during mild to moderate oxygen deprivation. Our prior studies have shown that cerebral neuronal NO synthase (nNOS) is essential for [NO] responses to decreased oxygen tension and that endothelial NO synthase (eNOS) is of little consequence. In this study, we explored the mechanisms of three specific cotransporters known to play a role in the hypoxic state: KB-R7943 for blockade of the Na+/Ca2+ exchanger, bumetanide for the Na+-K+-2Cl cotransporter, and amiloride for Na+/H+ cotransporters. In vivo measurements of arteriolar diameter and [NO] at normal and locally reduced oxygen tension in the rat parietal cortex provided the functional analysis. As previously found for intestinal arterioles, bumetanide- sensitive cotransporters are primarily responsible for sensing reduced oxygen because the increased [NO] and dilation were suppressed. The Na+/Ca2+ exchanger facilitated increased NO formation because blockade also suppressed [NO] and dilatory responses to decreased oxygen. Amiloride-sensitive Na+/H+ cotransporters did not significantly contribute to the microvascular regulation. To confirm that nNOS rather than eNOS was primarily responsible for NO generation, eNOS was suppressed with the fusion protein cavtratin for the caveolae domain of eNOS. Although the resting [NO] decreased and arterioles constricted as eNOS was suppressed, most of the increased NO and dilatory response to oxygen were preserved because nNOS was functional. Therefore, nNOS activation secondary to Na+-K+- 2Cl- cotransporter and Na+/Ca2+ exchanger functions are key to cerebral vascular oxygen responses. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that specific hypoxic molecules, including hypoxia-inducible factor-1α (HIF-1α), neuronal nitric oxide synthase (nNOS), and vascular endothelial growth factor (VEGF), are upregulated within the cerebral cortex of acutely anemic rats. Isoflurane-anesthetized rats underwent acute hemodilution by exchanging 50% of their blood volume with pentastarch. Following hemodilution, mean arterial pressure and arterial PaO2 values did not differ between control and anemic rats while the hemoglobin concentration decreased to 57 ± 2 g/l. In anemic rats, cerebral cortical HIF-1α protein levels were increased, relative to controls (1.7 ± 0.5-fold, P < 0.05). This increase was associated with an increase in mRNA levels for VEGF, erythropoietin, CXCR4, iNOS, and nNOS (P < 0.05 for all), but not endothelial NOS. Cerebral cortical nNOS and VEGF protein levels were increased in anemic rats, relative to controls (2.0 ± 0.2- and 1.5 ± 0.4-fold, respectively, P < 0.05 for both). Immunohistochemistry demonstrated increased HIF-1α and VEGF staining in perivascular regions of the anemic cerebral cortex and an increase in the number of nNOS-positive cerebral cortical cells (3.2 ± 1.0-fold, P < 0.001). The nNOS-positive cells costained with the neuronal marker, Neu-N, but not with the astrocytic marker glial fibrillary acidic protein (GFAP). These nNOS-positive neurons frequently sent axonal projections toward cerebral blood vessels. Conversely, VEGF immunostaining colocalized with both neuronal (NeuN) and astrocytic markers (GFAP). In conclusion, acute normotensive, normoxemic hemodilution increased the levels of HIF-1α protein and mRNA for HIF-1-responsive molecules, nNOS and VEGF protein levels were also increased within the cerebral cortex of anemic rats at clinically relevant hemoglobin concentrations. [ABSTRACT FROM AUTHOR]

Induction of heme oxygenase-1 (HO-1) in renal tubules occurs as an adaptive and beneficial response in acute renal failure (ARF) following ischemia and nephrotoxins. Using an in vitro model of polarized Madin-Darby canine kidney (MDCK) epithelial cells, we examined apical and basolateral cell surface sensitivity to HO-1 induction by heme. Basolateral exposure to 5 μM hemin (heme chloride) resulted in higher HO-1 induction than did apical exposure. The peak induction of HO-1 by basolateral application of hemin occurred between 12 and 18 h of exposure and was dose dependent. Similar cell surface sensitivity to hemin-induced HO-1 expression was observed using a mouse cortical collecting duct cell line (94D cells). Hepatocyte growth factor (HGF) is known to decrease cell polarity of MDCK cells. Following pre-treatment with HGF, apically applied heroin gave greater stimulation of HO-1 expression, whereas HGF alone did not induce HO-1. We also examined the effect of hypoxia on hemin-mediated HO-1 induction. MDCK cells were subjected to hypoxia (1% O2) for 24 h to simulate the effects of ischemic ARF. Under hypoxic conditions, both apical as well as basolateral surfaces of MDCK were more sensitive to HO-1 induction by hemin. Hypoxia alone did not induce HO-1 but appeared to potentiate both apical and basolateral sensitivity to hemin-mediated induction. These data demonstrate that the induction of HO-1 expression in polarized renal epithelia by heme is achieved primarily via basolateral exposure. However, under conditions of altered renal epithelial cell polarity and hypoxia, increased HO-1 induction occurs following apical exposure to heme. [ABSTRACT FROM AUTHOR]

Hypoxia has been suspected to trigger transdifferentiation of renal tubular cells into myofibroblasts in an epithelial-to-mesenchymal transition (EMT) process. To determine the functional networks potentially altered by hypoxia, rat renal tubule suspensions were incubated under three conditions of oxygenation ranging from normoxia (lactate uptake) to severe hypoxia (lactate production). Transcriptome changes after 4 h were analyzed on a high scale by restriction fragment differential display. Among 1,533 transcripts found, 42% were maximally expressed under severe hypoxia and 8% under mild hypoxia (Po2 = 48 mmHg), suggesting two different levels of oxygen sensing. Normoxia was required for full expression of the proximal tubule-specific transcripts 25-hydroxyvitamin D 1-hydroxylase (Cyp27b1) and ʟ-pyruvate kinase (Pklr), transcripts involved in tissue cohesion such as fibronectin (Fn1) and N-cadherin (Cdh2), and non-muscle-type myosin transcripts. Mild hypoxia increased myogenin transcript level. Conversely, severe hypoxia increased transcripts involved in extracellular matrix remodeling, those of muscle-type myosins, and others involved in creatine phosphate synthesis and lactate transport (Slc16a7). Accordingly, microscopy showed loss of tubule aggregation under hypoxia, without tubular disruption. Hypoxia also increased the levels of kidney-specific transcripts normally restricted to the less oxygenated medullary zone and others specific for the distal part of the nephron. We conclude that extensive oxygen supply to the kidney tubule favors expression of its differentiated functions specifically in the proximal tubule, whose embryonic origin is mesenchymal. The phenotype changes could potentially permit transient adaptation to hypoxia but also favor pathological processes such as tissue invasion. [ABSTRACT FROM AUTHOR]

Hypertension is associated with increased levels of oxidative stress and medullary renal injury. Previous studies have shown that elevations in renal perfusion pressure increase Na+ delivery to the medullary thick ascending limb (mTAL), and enhancement of NaCl transport in the outer medulla has been reported in many experimental forms of hypertension. This study examined the effects of increased Na+ and fluid delivery in mTAL perfused in vitro on the generation of superoxide. Osmolality was maintained constant between low- and high-Na+ perfusates by adjusting with choline CI-. Real-time fluorescent microscopic techniques were used to determine the generation of superoxide and nitric oxide in individual mTAL cells using dihydroethidium and DAF-FM dyes, respectively. Increasing the Na+ concentration of the perfusate from 60 to 149 mM or luminal flow rate from 5 to 20 nl/min (with fixed Na+ concentration of 60 mM) significantly increased superoxide generation and decreased nitric oxide in mTAL. These effects were inhibited when active transport of Na+ was inhibited by ouabain. We conclude that increases in luminal Na+ concentration and/or flow rate can increase the generation of superoxide in mTAL and reduce nitric oxide bioavailability. This may lead to reduction in medullary blood flow and promote hypoxia and tubular necrosis within the renal medulla during in hypertension. [ABSTRACT FROM AUTHOR]

Acute isocapnic intermittent hypoxia elicits time-dependent, serotonin-dependent enhancement of phrenic motor output in anesthetized rats (phrenic long-term facilitation, pLTF). In adult rats, pLTF is enhanced by chronic intermittent hypoxia (CIH). To test the hypothesis that early postnatal CIH induces persistent modifications of ventilation and pLTF, we exposed male Sprague-Dawley rat pups on their first day of life to a CIH profile consisting of alternating room air and 10% oxygen every 90 s for 30 days during daylight hours (RAIH) or to comparable exposures consisting of room air throughout (RARA). One month after cessation of CIH, respiratory responses were recorded using whole body plethysmography, and integrated phrenic nerve activity was recorded in urethane-anesthetized, vagotomized, paralyzed, and ventilated rats at baseline and after exposures to three 5-min hypoxic episodes [inspired O2 fraction (FɪO2) = 0.11] separated by 5 min of hyperoxia (FɪO2 = 0.5). RAIH rats displayed greater normoxic ventilation and also increased burst frequency compared with RARA rats (P < 0.01). Ventilatory responses to hypoxia and short-term phrenic responses during acute hypoxic challenges were reduced in RAIH rats (P < 0.01). Although pLTF was present in both RAIH and RARA rats, it was diminished in RAIH rats (minute activity: 74 ± 2% in RARA vs. 55 ± 5% in RAIH at 60 min; P < 0.01). Thus we conclude that early postnatal CIH modifies normoxic and hypoxic ventilatory and phrenic responses that persist at 1 mo after cessation of CIH (i.e., metaplasticity) and markedly differ from previously reported increased neural plasticity changes induced by CIH in adult rats. [ABSTRACT FROM AUTHOR]

Exposure to mild hypoxia elicits a characteristic cerebrovascular response in mammals, including humans. Initially, cerebral blood flow (CBF) increases as much as twofold. The blood flow increase is blunted somewhat by a decreasing arterial Pco2 as a result of the hypoxia-induced hyperventilatory response. After a few days, CBF begins to fall back toward baseline levels as the blood oxygen-carrying capacity is increasing due to increasing hemoglobin concentration and packed red cell volume as a result of erythropoietin upregulation. By the end of 2 wk of hypoxic exposure, brain capillary density has increased with resultant decreased intercapillary distances. The relative time courses of these changes suggest that they are adjusted by different control signals and mechanisms. The CBF response appears linked to the blood oxygen-carrying capacity, whereas the hypoxia-induced brain angiogenesis appears to be in response to tissue hypoxia. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor (HIF)-1 is a transcription factor mediating cellular response to hypoxia. Although it is expressed in tubular cells of the ischemic kidney, its functional role is not fully clarified in the pathological context. In this study, we investigated a role of HIF in tubular cell apoptosis induced by cisplatin. HIF-1α was expressed in tubular cells in the outer medulla 3 days after cisplatin (6 mg/kg) administration. With the in vivo administration of cobalt to activate HIF, the number of apoptotic renal tubular cells became much smaller in the outer medulla, compared with the vehicle group. We also examined the functional role of HIF-1 in vitro using immortalized rat proximal tubular cells (IRPTC). In hypoxia, IRPTC that express dominant-negative (dn) HIF-1α showed impaired survival in cisplatin injury at variable doses (25-100 μM, 24 h), which was not obvious in normoxia: The observed difference in cell viability in hypoxia was associated with the increased number of apoptotic cells in dnHIF-1α clones (Hoechst 33258 staining). Studies on intracellular signaling revealed that the degree of cytochrome c release, dissipation of mitochondrial membrane potentials, and caspase-9 activity were all more prominent in dnHIF-1α clones than in control IRPTC, pointing to the accelerated signaling of mitochondrial pathways. We propose that HIF-1 mediates cytoprotection against cisplatin injury in hypoxic renal tubular cells, by reducing the number of apoptotic cells through stabilization of mitochondrial membrane integrity and suppression of apoptosis signaling. A possibility was suggested that activation of HIF-1 could be a new promising therapeutic target for hypoxic renal diseases. [ABSTRACT FROM AUTHOR]

Transactivation of the DNA-binding proteins nuclear factor-κB (NF-κB) and activator protein (AP)-1 by de novo oxyradical generation is a stereotypic redox-sensitive process during hypoxic stress of the liver. Systemic trauma is associated with splanchnic hypoxia-reoxygenation (H/R) followed by intraportal gram-negative bacteremia, which collectively have been implicated in posttraumatic liver dysfunction and multiple organ damage. We hypothesized that hypoxic stress of the liver before stimulation by Escherichia coli serotype O55:B5 (EC) amplifies oxyradical-mediated transactivation of NF-κB and AP-1 as well as cytokine production compared with noninfectious H/R or gram-negative sepsis without prior hypoxia. Livers from Sprague-Dawley rats underwent perfusion for 180 min with or without 0.5 h of hypoxia (perfusate Po2, 40 ± 5 mmHg) followed by reoxygenation and infection with 109 EC or 0.9% NaC1 infusion. In H/R + EC livers, nuclear translocation of NF-κB and AP-1 was unexpectedly reduced in gel shift assays vs. normoxic EC controls, as were perfusate TNF-α and IL-1β levels. Preceding hypoxic stress paradoxically increased postbacteremic reduced-to-oxidized glutathione ratios plus nuclear localization of IκBα and phospho-IκBα, but not JunB/FosB profiles. Notably, xanthine oxidase inhibition increased transactivation as well as cytokine production in H/R + EC livers. Thus brief hypoxic stress of the liver before intraportal gram-negative bacteremia potently suppresses activation of canonical redox-sensitive transcription factors and production of inflammatory cytokines by mechanisms including xanthine oxidaseinduced oxyradicals functioning in an anti-inflammatory signaling role. These results suggest a novel multifunctionality of oxyradicals in decoupling hepatic transcriptional activity and cytokine biosynthesis early in the posttraumatic milieu. [ABSTRACT FROM AUTHOR]

Examines the effects of nocturnal hypoxic exposures (NHE) on the cerebrovascular responses to acute hypoxia and hypercapnia in humans. Timing and sequence of overnight, blood, and acute dynamic measurements; Sensitivity of cerebral blood flow to acute variations in hypoxia; Physiological and symptomatic responses to NHE.

Serotonin receptor subtypes required for ventilatory long-term facilitation and its enhancement after chronic intermittent hypoxia in awake rats. Respiratory long-term facilitation (LTF), a serotonin-dependent, persistent augmentation of respiratory activity after episodic hypoxia, is enhanced by pretreatment of chronic intermittent hypoxia (CIH; 5 min 11–12% O2-5 min air, 12 h/night for 7 nights). The present study examined the effects of methysergide (serotonin 5-HT1,2,5,6,7 receptor antagonist), ketanserin (5-HT2 antagonist), or clozapine (5-HT2,6,7 antagonist) on both ventilatory LTF and the CIH effect on ventilatory LTF in conscious male adult rats to determine which specific receptor subtype(s) is involved. In untreated rats (i.e., animals not exposed to CIH), LTF, induced by five episodes of 5-min poikilocapnic hypoxia (10% O2) separated by 5-min normoxic intervals, was measured twice by plethysmography. Thus the measurement was conducted 1–2 days before (as control) and ∼1 h after systemic injection of methysergide (1 mg/kg ip), ketanserin (1 mg/kg), or clozapine (1.5 mg/kg). Resting ventilation, metabolic rate, and hypoxic ventilatory response (HVR) were unchanged, but LTF (∼18% above baseline) was eliminated by each drug. In CIH-treated rats, LTF was also measured twice, before and ∼8 h after CIH. Vehicle, methysergide, ketanserin, or clozapine was injected ∼1 h before the second measurement. Neither resting ventilation nor metabolic rate was changed after CIH and/or any drug. HVR was unchanged after methysergide and ketanserin but reduced in four of seven clozapine rats. The CIH-enhanced LTF (∼28%) was abolished by methysergide and clozapine but only attenuated by ketanserin (to ∼10%). Collectively, these data suggest that ventilatory LTF requires 5-HT2 receptors and that the CIH effect on LTF requires non-5-HT2 serotonin receptors, probably 5-HT6 and/or 5-HT7 subtype(s). [ABSTRACT FROM AUTHOR]

The goal of the present study was to evaluate the effects of relatively short-term chronic intermittent hypoxia (CIH) on endothelial function of resistance vessels in the skeletal muscle and cerebral circulations. Sprague-Dawley rats were exposed to 14 days of CIH (10% fraction of inspired oxygen for 1 min at 4-min intervals, 12 h/day, n = 6). Control rats (n = 6) were housed under normoxic conditions. After 14 days, resistance arteries of the gracilis muscle (GA) and middle cerebral arteries (MCA) were isolated and cannulated with micropipettes, perfused and superfused with physiological salt solution, and equilibrated with 21% O[sub 2]-5% CO[sub 2] in a heated chamber. The arteries were pressurized to 90 mmHg, and vessel diameters were measured via a video micrometer before and after exposure to ACh (10[sup -7]-10[sup -4] M), sodium nitroprusside (10[sup -6] M), and acute reduction of Po[sub 2] in the perfusate/superfusate (from 140 to 40 mmHg). ACh-induced dilations of GA and MCA from animals exposed to CIH were greatly attenuated, whereas responses to nitroprusside were similar to controls. Dilations of both GA and MCA in response to acute reductions in Po[sub 2] were virtually abolished in animals exposed to CIH compared with controls. These findings suggest that exposure to CIH reduces the bioavailability of nitric oxide in the cerebral and skeletal muscle circulations and severely blunts vasodilator responsiveness to acute hypoxia. [ABSTRACT FROM AUTHOR]