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Tissue oxygen levels are tightly regulated in all organs. This poses a challenge for the kidney, as its function requires blood flow, and thus, oxygen delivery to greatly exceed its metabolic requirements. Because superoxide production in the kidney is dependent on oxygen availability, tissue hyperoxia could drive oxidative stress. In the mammalian renal cortex, this problem may have been solved, in part, through a structural antioxidant defense mechanism. That is, arteries and veins are closely associated in a countercurrent arrangement, facilitating diffusional arterial-to-venous (AV) oxygen shunting. Because of this mechanism, a proportion of the oxygen delivered in the renal artery never reaches kidney tissue but instead diffuses to the closely associated renal veins, thus limiting oxygen transport to tissue. In the nonmammalian kidney, arteries and veins are not arranged in an intimate countercurrent fashion as in mammals; thus AV oxygen shunting is likely less important in regulation of kidney oxygenation in these species. Instead, the kidney's blood supply is predominately of venous origin. This likely has a similar impact on tissue oxygenation as AV oxygen shunting, of limiting delivery of oxygen to renal tissue. Thus, we hypothesize the evolution of structural antioxidant mechanisms that are anatomically divergent but functionally homologous in the mammalian and nonmammalian kidney. hyperoxia; hypoxia; kidney circulation; oxidative stress; portal system doi: 10.1152/ajpregu.00364.2010.

We used a mathematical model of [O.sub.2] transport and the urine concentrating mechanism of the outer medulla of the rat kidney to study the effects of blood pH and medullary blood flow on [O.sub.2] availability and [Na.sup.+] reabsorption. The model predicts that in vivo paracellular [Na.sup.+] fluxes across medullary thick ascending limbs (toTALs) are small relative to transcellular [Na.sup.+] fluxes and that paracellular fluxes favor [Na.sup.+] reabsorption from the lumen along most of the mTAL segments. In addition, model results suggest that blood pH has a significant impact on [O.sub.2] transport and Nat reabsorption owing to the Bohr effect, according to which a lower pH reduces the binding affinity of hemoglobin for [O.sub.2]. Thus our model predicts that the presumed greater acidity of blood in the interbundle regions, where mTALs are located, relative to that in the vascular bundles, facilitates the delivery of [O.sub.2] to support the high metabolic requirements of the mTALs and raises the concentrating capability of the outer medulla. Model results also suggest that increases in vascular and tubular flow rates result in disproportional, smaller increases in active [O.sub.2] consumption and mTAL active [Na.sup.+] transport, despite the higher delivery of [O.sub.2] and [Na.sup.+]. That is, at a sufficiently high medullary [O.sub.2] supply, [O.sub.2] demand in the outer medulla does not adjust precisely to changes in [O.sub.2] delivery. mathematical model; thick ascending limb; [T.sub.Na]/[Qo.sub.2] ratio; paracellular; transcellular doi: 10.1152/ajprenal.00572.2009.

We examined the mechanisms that maintain stable renal tissue [Po.sub.2] during moderate renal ischemia, when changes in renal oxygen delivery ([??]o.sub.2]) and consumption ([[??]o.sub.2]) are mismatched. When renal artery pressure (RAP) was reduced progressively from 80 to 40 mmHg, [[??]o.sub.2] (-38 [+ or -] 7%) was reduced more than [Do.sub.2] (-26 [+ or -] 4%). Electrical stimulation of the renal nerves (RNS) reduced [Do.sub.2] (-49 [+ or -] 4% at 2 Hz) more than [[??]o.sub.2] (-30 [+ or -] 7% at 2 Hz). Renal arterial infusion of angiotensin II reduced [Do.sub.2] (-38 [+ or -] 3%) but not [[??]o.sub.2] (+ 10 [+ or -] 10%). Despite mismatched changes in [[??]o.sub.2] and [[??]o.sub.2], renal tissue [Po.sub.2] remained remarkably stable at [greater than or equal to] 40 mmHg RAP, during RNS at [less than or equal to] 2 Hz, and during angiotensin II infusion. The ratio of sodium reabsorption to [[??]o.sub.2] was reduced by all three ischemic stimuli. None of the stimuli significantly altered the gradients in P[co.sub.2] or pH across the kidney. Fractional oxygen extraction increased and renal venous Po2 fell during 2-Hz RNS and angiotensin II infusion, but not when RAP was reduced to 40 mmHg. Thus reduced renal [[??]o.sub.2] can help. prevent tissue hypoxia during mild renal ischemia, but when renal [[??]o.sub.2] is reduced less than [[??]o.sub.2], other mechanisms prevent a fall in renal [Po.sub.2]. These mechanisms do not include increased efficiency of renal oxygen utilization for sodium reahsorption or reduced washout of carbon dioxide from the kidney, leading to increased oxygen extraction. However, increased oxygen extraction could be driven by altered countercurrent exchange of carbon dioxide and/or oxygen between renal arteries and veins. angiotensin II; carbon dioxide; hypoxia; hypotension; oxygen; sympathetic nervous system doi: 10.1152/ajprenal.00647.2009

The effect of low blood flow at onset of moderate-intensity exercise on the rate of rise in muscle oxygen uptake was examined. Seven male subjects performed a 3.5-min one-legged knee-extensor exercise bout (24 [+ or -] 1 W, mean [+ or -] SD) without (Con) and with (double blockade; DB) arterial infusion of inhibitors of nitric oxide synthase (NG-monomethyl-L-arginine) and cyclooxygenase (indomethacin) to inhibit the synthesis of nitric oxide and prostanoids, respectively. Leg blood flow and leg oxygen delivery throughout exercise was 25-50% lower (P < 0.05) in DB compared with Con. Leg oxygen extraction (arteriovenous O2 difference) was higher (P < 0.05) in DB than in Con (5 s: 127 [+ or -] 3 vs. 56 [+ or -] 4 ml/1), and leg oxygen uptake was not different between Con and DB during exercise. The difference between leg oxygen delivery and leg oxygen uptake was smaller (P < 0.05) during exercise in DB than in Con (5 s: 59 [+ or -] 12 vs. 262 [+ or -] 39 ml/min). The present data demonstrate that muscle blood flow and oxygen delivery can be markedly reduced without affecting muscle oxygen uptake in the initial phase of moderate-intensity exercise, suggesting that blood flow does not limit muscle oxygen uptake at the onset of exercise. Additionally, prostanoids and/or nitric oxide appear to play important roles in elevating skeletal muscle blood flow in the initial phase of exercise. oxygen delivery; oxygen extraction; nitric oxide; prostanoids doi:10.1152/ajpregu.00730.2009

The increase in [O.sub.2] tension after birth is a major factor stimulating ductus arteriosus (DA) constriction and closure. Here we studied the role of the mitochondrial electron transport chain (ETC) as sensor, [H.sub.2][O.sub.2] as mediator, and voltage-gated potassium ([K.sub.v]) channels and Rho kinase as effectors of [O.sub.2]-induced contraction in the chicken DA during fetal development. Switching from 0% to 21% [O.sub.2] contracted the pulmonary side of the mature DA (mature pDA) but had no effect in immature pDA and relaxed the aortic side of the mature DA (mature aDA). This contraction of the pDA was attenuated by inhibitors of the mitochondrial ETC and by the [H.sub.2][O.sub.2] scavenger polyethylene glycol (PEG)-catalase. Moreover, [O.sub.2] increased reactive oxygen species (ROS) production, measured with the fluorescent probes dihydroethidium and 2',7'-dichlorofluorescein, only in mature pDA. The [H.sub.2][O.sub.2] analog t-butyl-hydroperoxide mimicked the responses to 02 in the three vessels. In contrast to immature pDA cells, mature pDA cells exhibited high-amplitude [O.sub.2]-sensitive potassium currents. The Kv channel blocker 4-aminopyridine prevented the current inhibition elicited by [O.sub.2]. The L-type [Ca.sup.2+] ([Ca.sub.L]) channel blocker nifedipine and the Rho kinase inhibitors Y-27632 and hydroxyfasudil induced a similar relaxation when mature pDA were stimulated with [O.sub.2] or [H.sub.2][O.sub.2]. Moreover, the sensitivity to these drugs increased with maturation. Our results indicate the presence of a common mechanism for [O.sub.2] sensing/signaling in mammalian and nonmammalian DA and favor the idea that, rather than a single mechanism, a parallel maturation of the sensor and effectors is critical for [O.sub.2] sensitivity appearance during development. oxygen sensing; potassium channels; hydrogen peroxide doi:10.1152/ajplung.00092.2009.

Chronic exposure to hypoxia is associated with muscle atrophy (i.e., a reduction in muscle fiber cross-sectional area), reduced oxidative capacity, and capillary growth. It is controversial whether these changes are muscle and fiber type specific. We hypothesized that different regions of the same muscle would also respond differently to chronic hypoxia. To investigate this, we compared the deep (oxidative) and superficial (glycolytic) region of the plantaris muscle of eight male rats exposed to 4 wk of hypobaric hypoxia (410 mmHg, [Po.sub.2]:11.5 kPa) with those of nine normoxic rats. Hematocrit was higher in chronic hypoxic than control rats (59% vs. 50%, P < 0.001). Using histochemistry, we observed 10% fiber atrophy (P < 0.05) in both regions of the muscle but no shift in the fiber type composition and myoglobin concentration of the fibers. In hypoxic rats, succinate dehydrogenase (SDH) activity was elevated in fibers of each type in the superficial region (25%, P < 0.05) but not in the deep region, whereas in the deep region but not the superficial region the number of capillaries supplying a fiber was elevated (14%, P < 0.05). Model calculations showed that the region-specific alterations in fiber size, SDH activity, and capillary supply to a fiber prevented the occurrence of anoxic areas in the deep region but not in the superficial region. Inclusion of reported acclimatization-induced increases in mean capillary oxygen pressure attenuated the development of anoxic tissue areas in the superficial region of the muscle. We conclude that the determinants of tissue oxygenation show region-specific adaptations, resulting in a marked differential effect on tissue [Po.sub.2]. tissue oxygenation; capillarization; oxidative capacity

The majority of mitochondrial proteins are encoded by nuclear genes and synthesized in the cytosol as preproteins containing a mitochondria import sequence. Preproteins traverse the outer mitochondrial membrane in an unfolded state and then translocate through the inner membrane into the matrix via import machinery that includes mitochondrial heat shock protein 70 (mtHSP70). Neonatal rat cardiac myocytes (NCM) infected with an adenoviral vector expressing mtHSP70 or an empty control ([Adv.sup.-]) for 48 h were submitted to 8 h of simulated ischemia (hypoxia) followed by 16 h of reperfusion (reoxygenation). Infection with mtHSP70 virus yielded an increase in mtHSP70 protein in NCM mitochondria compared with [Adv.sup.-] (P < 0.05). Cell viability after simulated ischemia/reperfusion (I/R) was decreased in both [Adv.sup.-] and mtHSP70 groups, relative to control (P < 0.05), but mtHSP70-infected NCM had enhanced viability after I/R relative to Adv-infected NCM (P < 0.05). Simulated I/R caused an increase in reactive oxygen species generation and lipid peroxidation in Adv-infected NCM (P < 0.05, for both) that was not observed in mtHSP70-infected NCM. Mitochondrial complex III and IV activities were greater in mtHSP70-infected NCM after simulated I/R compared with [Adv.sup.-] (P < 0.05 for both). After simulated I/R, ATP content increased in mtHSP70-infected NCM, compared with [Adv.sup.-] (P < 0.05). Apoptotic markers were decreased in mtHSP70-infected NCM compared with [Adv.sup.-] after simulated I/R (P < 0.05). These results indicate that overexpression of mtHSP70 protects the mitochondria against damage from simulated I/R that may be due to a decrease in reactive oxygen species leading to preservation of mitochondrial complex function activities and ATP formation. ischemia; reperfusion; free radical scavenger

We sought to describe cerebrovascular responses to incremental exercise and test the hypothesis that changes in cerebral oxygenation influence maximal performance. Eleven men cycled in three conditions: 1) sea level (SL); 2) acute hypoxia [AH; hypobaric chamber, inspired [Po.sub.2] ([Pi.sub.o.sub.2]) 86 Torr]; and 3) chronic hypoxia [CH; 4,300 m, [Pi.sub.o.sub.2], 86 Torr]. At maximal work rate ([W.sub.max]), fraction of inspired oxygen ([Fi.sub.o.sub.2]) was surreptitiously increased to 0.60, while subjects were encouraged to continue pedaling. Changes in cerebral (frontal lobe) ([C.sub.ox]) and muscle (vastus lateralis) oxygenation ([M.sub.ox]) (near infrared spectroscopy), middle cerebral artery blood flow velocity (MCA [V.sub.mean]; transcranial Doppler), and end-tidal [Pco.sub.2] ([Pet.sub.co.sub.2]) were analyzed across % [W.sub.max] (significance at P < 0.05). At SL, [Pet.sub.co.sub.2], MCA [V.sub.mean], and [C.sub.ox] fell as work rate rose from 75 to 100% [W.sub.max]. During AH, [Pet.sub.co.sub.2] and MCA [V.sub.mean], declined from 50 to 100% [W.sub.max], while [C.sub.ox] fell from rest. With CH, [Pet.sub.co.sub.2] and [C.sub.ox] dropped throughout exercise, while MCA [V.sub.mean] fell only from 75 to 100% [W.sub.max]. [M.sub.ox] fell from rest to 75% [W.sub.max] at SL and AH and throughout exercise in CH. The magnitude of fall in [C.sub.ox], but not [M.sub.ox], was different between conditions (CH > AH > SL). [Fi.sub.o.sub.2] 0.60 at [W.sub.max] did not prolong exercise at SL, yet allowed subjects to continue for 96 [+ or -] 61 s in AH and 162 [+ or -] 90 s in CH. During [Fi.sub.o.sub.2] 0.60, [C.sub.ox] rose and [M.sub.ox] remained constant as work rate increased. Thus cerebral hypoxia appeared to impose a limit to maximal exercise during hypobaric hypoxia ([Pi.sub.o.sub.2] 86 Torr), since its reversal was associated with improved performance. altitude; near infrared spectroscopy; cerebral blood flow; fatigue; muscle oxygenation

High altitude decreases birth weight, but this effect is diminished in long vs. short-resident, high-altitude populations. We asked whether women from long vs. short-resident, high-altitude populations had higher arterial oxygenation levels by comparing 42 Andean and 26 European residents of La Paz, Bolivia (3,600 m), serially during pregnancy (weeks 20, 30, and 36) and again 4 mo postpartum. Pregnancy raised hypoxic ventilatory sensitivity threefold, resting ventilation ([V.sub.E]), and arterial [O.sub.2] saturation ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCI..]) in both groups. Ancestry, as identified using 81 genetic markers, correlated with respiratory pattern, such that greater Andean ancestry was associated with higher respiratory frequency and lower tidal volume. Pregnancy increased total blood and plasma volume ~40% in both groups without changing red blood cell mass relative to body weight; hence, hemoglobin fell. The hemoglobin decline was compensated for by the rise in [V.sub.E] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] with the result that arterial [O.sub.2] content ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]) was maintained near nonpregnant levels in both groups. Birth weights were similar for all Andean and European babies, but after adjusting for variation in gestational age, maternal height and parity, Andeans weighed 209 g more than Europeans. Babies with heavier birth weights and greater ponderal indices were born to Andean women with higher [V.sub.E] during pregnancy. We concluded that while maternal [V.sub.E] and arterial oxygenation were important, some factor other than higher [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] was responsible for protecting Andeans from altitude-associated reductions in fetal growth. hypoxia; ventilation; ventilatory control; infant birth weight; fetal growth; genetics of birth weight: human adaptation; respiratory pattern

Multigenerational (Andean) compared with shorter-term (European) high-altitude residents exhibit less hypoxia-associated reductions in birth weight. Because differences in arterial [O.sub.2] content are not responsible, we asked whether greater pregnancy-associated increases in uterine artery (UA) blood flow and [O.sub.2] delivery were involved. Serial studies were conducted in 42 Andean and 26 European residents of La Paz, Bolivia (3600 m) at weeks 20, 30, 36 of pregnancy and 4 mo postpartum using Doppler ultrasound. There were no differences postpartum but Andean vs. European women had greater UA diameter (0.65 [+ or -] 0.01 vs. 0.56 [+ or -] 0.01 cm), cross-sectional area (33.1 [+ or -] 0.97 vs. 24.7 [+ or -] 1.18 [mm.sup.2]), and blood flow at week 36 (743 [+ or -] 87 vs. 474 [+ or -] 36 ml/min) (all P < 0.05) and thus 1.6-fold greater uteroplacental [O.sub.2] delivery near term (126.82 [+ or -] 18.47 vs. 80.33 [+ or -] 8.69 ml [O.sub.2]*ml [blood.sup.-1]*[min.sup.-1], P < 0.05). Andeans had greater common iliac (CI) flow and lower external iliac relative to CI flow (0.52 [+ or -] 0.11 vs. 0.95 [+ or -] 0.14, P < 0.05) than Europeans at week 36. After adjusting for gestational age, maternal height, and parity, Andean babies weighed 209 g more than the Europeans. Greater UA cross-sectional area at week 30 related positively to birth weight in Andeans (r = +0.39) but negatively in Europeans (r = -0.37) (both P < 0.01). We concluded that a greater pregnancy-associated increase in UA diameter raised UA blood flow and uteroplacental [O.sub.2] delivery in the Andeans and contributed to their ability to maintain normal fetal growth under conditions of high-altitude hypoxia. These data implicate the involvement of genetic factors in protecting multigenerational populations from hypoxia-associated reductions in fetal growth, but future studies are required for confirmation and identification of the specific genes involved. birth weight; genetic adaptation; hypoxia; small-for-gestational age; uteroplacental vascular resistance

Several pulmonary and neurological conditions, both in the newborn and adult, result in hypercapnia. This leads to disturbances in normal pH homeostasis. Most mammalian cells maintain tight control of intracellular pH ([pH.sub.i]) using a group of transmembrane proteins that specialize in acid-base transport. These acid-base transporters are important in adjusting [pH.sub.i] during acidosis arising from hypoventilation. We hypothesized that exposure to chronic hypercapnia induces changes in the expression of acid-base transporters. Neonatal and adult CD-1 mice were exposed to either 8% or 12% C[O.sub.2] for 2 wk. We used Western blot analysis of membrane protein fractions from heart, kidney, and various brain regions to study the response of specific acid-base transporters to C[O.sub.2]. Chronic C[O.sub.2] increased the expression of the sodium hydrogen exchanger 1 (NHE1) and electroneutral sodium bicarbonate cotransporter (NBCn1) in the cerebral cortex, heart, and kidney of neonatal but not adult mice. C[O.sub.2] increased the expression of electrogenic NBC (NBCe1) in the neonatal but not the adult mouse heart and kidney. Hypercapnia decreased the expression of anion exchanger 3 (AE3) in both the neonatal and adult brain but increased AE3 expression in the neonatal heart. We conclude that: 1) chronic hypercapnia increases the expression of the acid extruders NHE1, NBCe1 and NBCn1 and decreases the expression of the acid loader AE3, possibly improving the capacity of the cell to maintain [pH.sub.i] in the face of acidosis; and 2) the heterogeneous response of tissues to hypercapnia depends on the level of C[O.sub.2] and development. anion exchanger; sodium bicarbonate cotransporter; sodium hydrogen exchanger; acidosis; hypercapnia

Tissue [Po.sub.2] (t[Po.sub.2]) reflects the balance between local [O.sub.2] supply and demand and, thus, could be a useful monitoring modality. However, the consistency and amplitude of the t[Po.sub.2] response in different organs during different cardiorespiratory insults is unknown. Therefore, we investigated the effects of endotoxemia, hemorrhage, and hypoxemia on t[Po.sub.2] measured in deep and peripheral organ beds. We compared arterial pressure, blood gas and lactate levels, descending aortic and renal blood flow, and t[Po.sub.2] in skeletal muscle, bladder epithelium, liver, and renal cortex during 1) LPS infusion (10 mg/kg), 2) sequential removal of 10% of circulating blood volume, and 3) reductions in inspired 02 concentration in an anesthetized Wistar rat model with values measured in sham-operated animals. Different patterns were seen in each of the shock states, with condition-specific variations in the degree of acidemia, lactatemia, and tissue [O.sub.2] responses between organs. Endotoxemia resulted in a rise in bladder t[Po.sub.2] and an early fall in liver t[Po.sub.2] but no significant change in muscle and renal cortical t[Po.sub.2]. Progressive hemorrhage, however, produced proportional declines in liver, muscle, and bladder t[Po.sub.2], but renal conical t[Po.sub.2] was maintained until profound blood loss had occurred. By contrast, progressive hypoxemia resulted in proportional decreases in t[Po.sub.2] in all organ beds. This study highlights the heterogeneity of responses in different organ beds during different shock states that are likely related to local changes in [O.sub.2] supply and utilization. Whole body monitoring is not generally reflective of these changes. tissue oxygen tension; hemodynamics; rat; endotoxemia; hemorrhage; hypoxemia doi:10.1152/ajpheart.00052.2006

It has been proposed by Saltin (J Exp Biol 115: 345-354, 1985) that oxygen delivery by blood is limiting for maximal work and oxygen consumption in humans during whole body exercise but not during single-muscle exercise. To test this prediction quantitatively, we developed a static (steady-state) computer model of oxygen transport to and within human skeletal muscle during single-muscle (quadriceps) exercise and whole body (cycling) exercise. The main system fluxes, namely cardiac output and oxygen consumption by muscle, are described as a function of the 'primary' parameter: work rate. The model is broadly validated by comparison of computer simulations with various experimental data. In silico studies show that, when all other parameters and system properties are kept constant, an increase in the working muscle mass from 2.5 kg (single quadriceps) to 15 kg (two legs) causes, at some critical work intensity, a drop in oxygen concentration in muscle cells to (very near) zero, and therefore oxygen supply by blood limits maximal oxygen consumption and oxidative ATP production. Therefore, the maximal oxygen consumption per muscle mass is significantly higher during single-muscle exercise than during whole body exercise. The effect is brought about by a distribution of a limited amount of oxygen transported by blood in a greater working muscle mass during whole body exercise. oxygen transport; oxygen consumption; muscle exercise doi:10.1152/ajpheart.01371.2006

Barrier dysfunction, involving the endothelium or epithelium, is implicated in the pathophysiology of many disease states, including acute and ventilator-associated lung injury. Evidence from cell culture, in vivo and clinical studies, has identified myosin light chain kinase as a drug discovery target for such diseases. Here, we measured disease-relevant end points to test the hypothesis that inhibition of myosin light chain kinase is a potential therapeutic target for treatment of barrier dysfunction resulting from acute lung injury. We used a combined gene knockout and chemical biology approach with an in vivo intact lung injury model. We showed that inhibition of myosin light chain kinase protects lung function, preserves oxygenation, prevents acidosis, and enhances survival after endotoxin exposure with subsequent mechanical ventilation. This protective effect provided by the small molecule inhibitor of myosin light chain kinase is present when the inhibitor is administered during a clinically relevant injury paradigm after endotoxin exposure. Treatment with inhibitor confers additional protection against acute lung injury to that provided by a standard protective mode of ventilation. These results support the hypothesis that myosin light chain kinase is a potential therapeutic target for acute lung injury and provide clinical end points of arterial blood gases and pulmonary compliance that facilitate the direct extrapolation of these studies to measures used in critical care medicine. endothelium; acute respiratory distress syndrome; protein kinase; oxygenation doi:10.1152/ajplung.00380.2006.

Portal branch ligation (PBL) may prevent liver failure after extended hepatic resection. However, clinical studies indicate that tumors within the ligated lobe develop accelerated growth. Although it is well known that tumor growth depends on the host's microvascularization, there is no information about how PBL affects the hepatic microcirculation. Our aims were to determine hepatic artery response, liver microcirculation, tissue oxygenation, and cell proliferation after PBL. Therefore, we used intravital multifluorescence microscopy, laser-Doppler flowmetry, immunohistochemistry, and biochemical techniques to examine microcirculatory responses, microvascular remodeling, and cellular consequences after left lateral PBL in BALB/c mice. During the first 7 days, PBL induced a reduction of left hilar blood flow by ~50%. This resulted in 80% sinusoidal perfusion failure, significant parenchymal hypoxia, and liver atrophy. After 14 days, however, left hilar blood flow was found to be restored. However, remodeling of the microvasculature included a rarefaction of the sinusoidal network, however, without substantial perfusion failure, compensated by a hepatic arterial buffer response and significant sinusoidal dilatation. This resulted in normalization of tissue oxygenation, indicating arterialization of the ligated lobe. Interestingly, late microvascular remodeling was associated with increased endothelial nitric oxide synthase expression, significant hepatocelhilar proliferation, and weight gain of the ligated lobe. Thus PBL induces only an initial microcirculatory failure with liver atrophy, followed by a hepatic arterial buffer response, microvascular remodeling, normoxygenation, and hepatocellular proliferation. This may explain the accelerated tumor progression occasionally observed in patients after PBL. liver; microcirculation doi: 10.1152/ajpgi.00503.2006

Kidney proximal tubules develop a severe but highly reversible energetic deficit due to nonesterified fatty acid (NEFA)-induced dissipation of mitochondrial membrane potential ([DELTA][PSI]m) during reoxygenation after severe hypoxia. To assess the mechanism for this behavior, we have compared the efficacies of different NEFA for inducing mitochondrial deenergization in permeabilized tubules measured using safranin O uptake and studied the modification of NEFA-induced deenergization by inhibitors of the ADP/ATP carrier and glutamate using both normoxic tubules treated with exogenous NEFA and tubules deenergized during hypoxia-reoxygenation (H/R). Among the long-chain NEFA that accumulate during H/R of isolated tubules and ischemia-reperfusion of the kidney in vivo, oleate, linoleate, and arachidonate had strong effects to dissipate [DELTA][[PSI].sub.m] that were slightly greater than palmitate, while stearate was inactive at concentrations reached in the cells. This behavior correlates well with the protonophoric effects of each NEFA. Inhibition of the ADP/ATP carrier with either carboxyatractyloside or bongkrekic acid or addition of glutamate to compete for the aspartate/ glutamate carrier improved [DELTA][[PSI].sub.m] in the presence of exogenous oleate and after H/R. Effects on the two carders were additive and restored safranin O uptake to as much as 80% of normal under both conditions. The data strongly support NEFA cycling across the inner mitochondrial membrane using anion carriers as the main mechanism for NEFA-induced deenergization in this system and provide the first evidence for a contribution of this process to pathophysiological events that impact importantly on energetics of intact cells. acute renal failure; kidney; membrane potential; mitochondria doi:10.1152/ajprenal.00476.2006.

Mathematical simulations of oxygen delivery to tissue from capillaries that take into account the particulate nature of blood flow predict the existence of oxygen tension (P[O.sub.2]) gradients between erythrocytes (RBCs). As RBCs and plasma alternately pass an observation point, these gradients are manifested as rapid fluctuations in P[O.sub.2], also known as erythrocyte-associated transients (EATs). The impact of hemodilution on EATs and oxygen delivery at the capillary level of the microcirculation has yet to be elucidated. Therefore, in the present study, phosphorescence quenching microscopy was used to measure EATs and P[O.sub.2] in capillaries of the rat spinotrapezius muscle at the following systemic hematocrits ([Hct.sub.sys]): normal (39%) and after moderate (HES 1; 27%) or severe (HES2; 15%) isovolemic hemodilution using a 6% hetastarch solution. A 532-nm laser, generating 10-[micro]s pulses concentrated onto a 0.9-[micro]m spot, was used to obtain plasma P[O.sub.2] values 100 times/s at points along surface capillaries of the muscle. Mean capillary P[O.sub.2] (PC[O.sub.2]; means [+ or -] SE) significantly decreased between conditions (normal: 56 [+ or -] 2 mmHg, n = 45; HESI: 47 [+ or -] 2 mmHg, n = 62; HES2: 27 [+ or -] 2 mmHg, n = 52, where n = capillary number). In addition, the magnitude of P[O.sub.2] transients ([DELTA]P[O.sub.2]) significantly decreased with hemodilution (normal: 19 [+ or -] 1 mmHg, n = 45; HES1: 11 [+ or -] 1 mmHg, n = 62; HES2: 6 [+ or -] 1 mmHg, n = 52). Results suggest that the decrease in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] and [DELTA]P[O.sub.2] with hemodilution is primarily dependent on [Hct.sub.sys] and subsequent microvascular compensations. microcirculation; oxygen transport; erythrocytes; oxygen tension gradients; phosphorescence quenching microscopy doi:10.1152/ajpheart.00915.2006.

To further explore the limitations to maximal [O.sub.2] consumption (V[O.sub.2 max]) in exercise-trained skeletal muscle, six cyclists performed graded knee-extensor exercise to maximum work rate (W[R.sub.max]) in hypoxia (12% [O.sub.2]), hyperoxia (100% [O.sub.2]), and hyperoxia + femoral arterial infusion of adenosine (ADO) at 80% W[R.sub.max]. Arterial and venous blood sampling and thermodilution blood flow measurements allowed the determination of muscle [O.sub.2] delivery and [O.sub.2] consumption. At W[R.sub.max], [O.sub.2] delivery rose progressively from hypoxia (1.0 [+ or -] 0.04 l/min) to hyperoxia (1.20 [+ or -] 0.09 l/min) and hyperoxia + ADO (1.33 [+ or -] 0.05 l/min). Leg V[O.sub.2] max varied with [O.sub.2] availability (0.81 [+ or -] 0.05 and 0.97 [+ or -] 0.07 l/min in hypoxia and hyperoxia, respectively) but did not improve with ADO-mediated vasodilation (0.80 [+ or -] 0.09 l/min in hyperoxia + ADO). Although a vasodilatory reserve in the maximally working quadriceps muscle group may have been evidenced by increased leg vascular conductance after ADO infusion beyond that observed in hyperoxia (increased blood flow but no change in blood pressure), we recognize the possibility that the ADO infusion may have provoked vasodilation in nonexercising tissue of this limb. Together, these findings imply that maximally exercising skeletal muscle may maintain some vasodilatory capacity, but the lack of improvement in leg V[O.sub.2max] with significantly increased [O.sub.2] delivery (hyperoxia + ADO), with a degree of uncertainty as to the site of this dilation, suggests an ADO-induced mismatch between [O.sub.2] consumption and blood flow in the exercising limb. exercise; blood flow; vasodilatory reserve doi: 10.1152/ajpheart.01396.2006.

It has been postulated that unsuccessful resuscitation of victims of accidental hypothermia is caused by insufficient tissue oxygenation. The aim of this study was to test whether inadequate [O.sub.2] supply and/or malfunctioning [O.sub.2] extraction occur during rewarming from deep/profound hypothermia of different duration. Three groups of rats (n = 7 each) were used: group 1 served as normothermic control for 5 h; groups 2 and 3 were core cooled to 15[degrees]C, kept at 15[degrees]C for 1 and 5 h, respectively, and then rewarmed. In both hypothermic groups, cardiac output (CO) decreased spontaneously by >50% in response to cooling. [O.sub.2] consumption fell to less than one-third during cooling but recovered completely in both groups during rewarming. During hypothermia, circulating blood volume in both groups was reduced to approximately one-third of baseline, indicating that some vascular beds were critically perfused during hypothermia. CO recovered completely in animals rewarmed after 1 h (group 2) but recovered to only 60% in those rewarmed after 5 h (group 3), whereas blood volume increased to approximately three-fourths of baseline in both groups. Metabolic acidosis was observed only after 5 h of hypothermia (15[degrees]C). A significant increase in myocardial tissue heat shock protein 70 after rewarming in group 3, but not in group 2, indicates an association with the duration of hypothermia. Thus mechanisms facilitating [O.sub.2] extraction function well during deep/profound hypothermia, and, despite low CO, [O.sub.2] supply was not a limiting factor for survival in the present experiments. resuscitation; oxygen transport; oxygen consumption; heat shock protein 70; blood volume

At birth, the lung environment changes from low to relatively high [O.sub.2] tension. Pulmonary blood flow increases and pulmonary artery pressure decreases. Recent data suggest that pulmonary vascular calcium-sensitive [K.sup.+] channel (B[K.sub.Ca] activation mediates perinatal pulmonary vasodilation. Although B[K.sub.Ca] channel expression is developmentally regulated, the molecular mechanisms responsible for B[K.sub.Ca] expression remain unknown. We tested the hypothesis that the low-[O.sup.2] tension environment of the normal fetus modulates B[K.sub.Ca], channel expression. We analyzed B[K.sub.Ca] expression under conditions of hypoxia and normoxia both in vitro and in vivo. B[K.sub.Ca] [alpha]-subunit mRNA expression increased twofold in ovine pulmonary artery smooth muscle cell (PASMC) primary cultures maintained in hypoxia. In vivo, B[K.sub.Ca] expression was similarly affected by hypoxia. When adult Sprague-Dawley rats were placed in hypobaric hypoxic chambers for 3 wk, hypoxic animals showed an increase of threefold in the expression of B[K.sub.Ca] [alpha]- and more than twofold in the expression of B[K.sub.Ca] [[beta].sub.1]-subunit mRNA. Immunochemical staining was consistent with the genetic data. To assess transcriptional activation of the [beta]-subunit of the B[K.sub.Ca] both B[K.sub.Ca] [[beta].sub.]- and [[beta].sub.2]-subunit luciferase ([K.sub.Ca], [beta]:[luc.sup.+]) reporter genes were constructed. Hypoxia increased PASMC [K.sub.Ca] [beta]:[luc.sup.+] reporter expression by threefold and [K.sub.Ca] [beta]:[luc.sup.+] expression by 35%. Fetal PASMC treated with the hypoxia-inducible factor-1 mimetic deferoxamine showed a 63 and 41% increase in B[K.sub.Ca] channel [alpha]- and [[beta].sub.1]-subunit expression, respectively. Together, these results suggest that oxygen tension modulates B[K.sub.Ca] channel subunit mRNA expression, and the regulation is, at least in part, at the transcriptional level. hypoxia; oxygen sensing; hypoxia-inducible factor-1

The synthesis of adrenal steroids requires molecular oxygen. Because arterial hypoxemia is a common clinical condition, the purpose of the present study was to examine steroidogenesis in vitro under physiological changes in [O.sub.2] tension (P[O.sub.2]) in cells from human adrenal glands with aldosterone-secreting adenomas (ASA; n = 3) or with bilateral adrenal hyperplasia causing Cushing's syndrome (n = 4). A decrease in P[O.sub.2] from 150 mmHg (mild hyperoxia) to 80 mmHg had minimal effect on steroid production. A reduction to 40 mmHg (still well within the physiological range) significantly inhibited cAMP- and ACTH-stimulated aldosterone, cortisol, and dehydroepiandrosterone (DHEA) production from ASA. Furthermore, cortisol and DHEA production in cells from histologically normal tissue, adjacent to ASA and from bilateral adrenal hyperplasias, was also inhibited under a P[O.sub.2] of 40 mmHg. We conclude that physiological decreases in P[O.sub.2] to levels typical for adrenal venous P[O.sub.2] under mild hypoxia inhibit steroidogenesis. These studies may have implications for oxygen therapy in critically ill patients with functional adrenal insufficiency, as well as for therapeutic options in patients with adrenal neoplasms. oxygen; cortisol; dehydroepiandrosterone; adrenal cortex

The oxygen transport capacity of phospholipid vesicles encapsulating purified Hb (HbV) produced with a [Po.sub.2] at which Hb is 50% saturated ([P.sub.50]) of 8 (Hb[V.sub.8]) and 29 mmHg (Hb[V.sub.29]) was investigated in the hamster chamber window model by using microvascular measurements to determine oxygen delivery during extreme hemodilution. Two isovolemic hemodilution steps were performed with 5% recombinant albumin (rHSA) until Hct was 35% of baseline. Isovolemic exchange was continued using HbV suspended in rHSA solution to a total [Hb] of 5.7 g/dl in blood. [P.sub.50] was modified by coencapsulating pyridoxal 5'-phosphate. Final Hct was 11% for the HbV groups, with a plasma [Hb] of 2.1 [+ or -] 0.1 g/dl after exchange with Hb[V.sub.8] or Hb[V.sub.29]. A reference group was hemodiluted to Hct 11% with only rHSA. All groups showed stable blood pressure and heart rate. Arterial oxygen tensions were significantly higher than baseline for the HbV groups and the rHSA group and significantly lower for the HbV groups compared with the rHSA group. Blood pressure was significantly higher for the Hb[V.sub.8] group compared with the Hb[V.sub.29] group. Arteriolar and venular blood flows were significantly higher than baseline for the HbV groups. Microvascular oxygen delivery and extraction were similar for the HbV groups but lower for the rHSA group (P < 0.05). Venular and tissue [Po.sub.2] were statistically higher for the Hb[V.sub.8] vs. the Hb[V.sub.29] and rHSA groups (P < 0.05). Improved tissue [Po.sub.2] is obtained when red blood cells deliver oxygen in combination with a high- rather than low-affinity oxygen carrier. oxygen-carrying capacity; blood substitutes; tissue oxygen; hemoglobin oxygen affinity

The microvascular distribution of oxygen was studied in the arterioles and venules of the awake hamster window chamber preparation to determine the contribution of vascular smooth muscle relaxation to oxygen consumption of the microvascular wall during verapamil-induced vasodilatation. Verapamil HCl delivered in a 0.1 mg/kg bolus injection followed by a continuous infusion of 0.01 mg x [kg.sup.-1] x [min.sup.-1] caused significant arteriolar dilatation, increased microvascular flow and functional capillary density, and decreased arteriolar vessel wall transmural [Po.sub.2] difference. Verapamil caused tissue [Po.sub.2] to increase from 25.5 [+ or -] 4.1 mmHg under control condition to 32.0 [+ or -] 3.7 mmHg during verapamil treatment. Total oxygen released by the microcirculation to the tissue remained the same as at baseline. Maintenance of the same level of oxygen release to the tissue, increased tissue [Po.sub.2], and decreased wall oxygen concentration gradient are compatible if vasodilatation significantly lowers vessel wall oxygen consumption, which in this model appears to constitute an important oxygen-consuming compartment. These findings show that treatment with verapamil, which increases oxygen supply through vasodilatation. may further improve tissue oxygenation by lowering oxygen consumption of the microcirculation. vasoactivity: oxygen gradients; tissue oxygenation; microvessel metabolism

Research was conducted to examine intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1) expression in human dermal microvascular and umbilical vein endothelial cells exposed to various oxygen tensions in the presence or absence of tumor necrosis factor-alpha (TNF-alpha). Results suggest that in both endothelial cell types, the expression of VCAM-1 and ICAM-1 is directly associated with oxygen availability in that hypoxia does not stimulate but may even downregulate both adhesion molecules.

A study was conducted to determine whether the induction of fetal distal lung epithelial cells (FDLE) sodium ion transport by postnatal oxygen was permanent or reversible, as well as to examine possible mechanisms for the increased gene expression and functional activity of epithelial Na+ channel (ENaC) in FDLEs. Results showed that the physiological increase in O2 concentration increased distal lung epithelial Na+ transport. This increase was a reversible phenomenon and was likely to be mediated by an increase in reactive oxygen species that cause increased gene expression of ENaC.

Variation in the proteinase antiproteinase balance in the lung leads to an enhancement of type I collagen deposition, which is induced by oxygen exposure. The deposition of type I collagen is optimum after 14 days of exposure to 85% oxygen. There is an increase in the mRNA expression of interstitial collagenase, the tissue inhibitor of metalloproteinases and the transforming growth factor-beta1 prior to type I collagen increase. There are no variations in the mRNA expression of stromelysin.

Heterogeneity of local myocardial flow and oxidative metabolism. Am J Physiol Heart Circ Physiol 279: H1029-H1035, 2000.--In mammalian hearts, local myocardial flow (LMF) varies between 20 and 200% of the mean. It is not clear whether oxidative metabolism has a similar degree of heterogeneity. Therefore, we investigated the relation between LMF and local oxidative metabolism in isolated rabbit hearts. Buffer oxygenation with [sup.18][O.sub.2] resulted in labeled myocardial oxidation water ([H.sub..2][sup.18]O). In four hearts, myocardial oxygen consumption (MV[O.sub.2]) was calculated from the [H.sub.2][sup.18]O production and compared with that calculated according to Fick. In eight additional hearts, LMF was measured using microspheres. Coronary venous [H.sub.2][sup.18]O kinetics and local [H.sub.2][sup.18]O residues were determined and analyzed by mathematical modeling. MV[O.sub.2] recovery from [H.sub.2][sup.18]O was [is greater than] 93% compared with that according to Fick. LMF ranged from 1.91 to 11.24 ml[multiplied by][min.sup.-1] [multiplied by][g.sup.-1], and local [H.sub.2][sup.18]O residue ranged from 0.41 to 1.04 [micro]mol/g. Both variables correlated (r = 0.62, n = 64, P [is less than] 0.001). Measurements in nine hearts were fitted by modeling using capillary permeability-surface area products ([PS.sub.c]) from 2 to 10 ml[multiplied by][min.sup.-1][g.sup.-1]. With flow-proportional [PS.sub.c], a 3.33-fold difference in LMF was associated with a 6.45-fold difference in local MV[O.sub.2]. Both LMF and local oxidative metabolism are spatially heterogeneous, and they correlate to one another. myocardial oxidation water; oxygen-18 labeling; modeling

Busk, Morten, Frank B. Jensen, and Tobias Wang. Effects of feeding on metabolism, gas transport, and acid-base balance in the bullfrog Rana catesbeiana. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 278: R185-R195, 2000.--Massive feeding in ectothermic vertebrates causes changes in metabolism and acid-base and respiratory parameters. Most investigations have focused on only one aspect of these complex changes, and different species have been used, making comparison among studies difficult. The purpose of the present study was, therefore, to provide an integrative study of the multiple physiological changes taking place after feeding. Bullfrogs (Rana catesbeiana) partly submerged in water were fed meals (mice or rats) amounting to ~1/10 of their body weight. Oxygen consumption increased and peaked at a value three times the predigestive level 72-96 h after feeding. Arterial [PO.sub.2] decreased slightly during digestion, whereas hemoglobin-bound oxygen saturation was unaffected. Yet, arterial blood oxygen content was pronouncedly elevated because of a 60% increase in hematocrit, which appeared mediated via release of red blood cells from the spleen. Gastric acid secretion was associated with a 60% increase in plasma [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] concentration ([[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]]) 48 h after feeding. Arterial pH only increased from 7.86 to 7.94, because the metabolic alkalosis was countered by an increase in [PCO.sub.2] from 10.8 to 13.7 mmHg. Feeding also induced a small intracellular alkalosis in the sartorius muscle. Arterial pH and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] returned to control values 96-120 h after feeding. There was no sign of anaerobic energy production during digestion as plasma and tissue lactate levels remained low and intracellular ATP concentration stayed high. However, phosphocreatine was reduced in the sartorius muscle and ventricle 48 h after feeding. specific dynamic action; [O.sub.2] transport; alkaline tide; metabolites; high-energy phosphates

Radegran, G., and B. Saltin. Human femoral artery diameter in relation to knee extensor muscle mass, peak blood flow, and oxygen uptake. Am. J. Physiol. Heart Circ. Physiol. 278: H162-H167, 2000.--It is not known whether the diameter of peripheral conduit arteries may impose a limitation on muscle blood flow and oxygen uptake at peak effort in humans, and it is not clear whether these arteries are dimensioned in relation to the tissue volume they supply or, rather, to the type and intensity of muscular activity. In this study, eight humans, with a peak pulmonary oxygen uptake of 3.90 [+ or -] 0.31 (range 2.29-5.03) l/min during ergometer cycle exercise, performed one-legged dynamic knee extensor exercise up to peak effort at 68 [+ or -] 7 W (range 55-100 W). Peak values for knee extensor blood flow (thermodilution) and oxygen uptake of 6.06 [+ or -] 0.74 (range 4.75-9.52) l/min and 874 [+ or -] 124 (range 590-1,521) ml/min, respectively, were achieved. Pulmonary oxygen uptake reached a peak of 1.72 [+ or -] 0.19 (range 1.54-2.33) l/min. Diameters of common and profunda femoral arteries determined by ultrasound Doppler were 10.6 [+ or -] 0.4 (range 8.2-12.7) and 6.0 [+ or -] 0.4 (range 4.5-8.0) mm, respectively. Thigh and quadriceps muscle volume measured by computer tomography were 10.06 [+ or -] 0.66 (range 6.18-10.95) and 2.36 [+ or -] 0.19 (range 1.31-3.27) liters, respectively. The common femoral artery diameter, but not that of the profunda branch, correlated with the thigh volume and quadriceps muscle mass. There were no relationships between either of the diameters and the absolute or muscle mass-related resting and peak values of blood flow and oxygen uptake, peak pulmonary oxygen uptake, or peak power output during knee extensor exercise. However, common femoral artery diameter correlated to peak pulmonary oxygen uptake during ergometer cycle exercise. In conclusion, common and profunda femoral artery diameters are sufficient to ensure delivery to the quadriceps muscle. However, the common branch may impose a limitation during ergometer cycle exercise. exercise; hyperemia; ultrasound Doppler

in this paper I present some ideas related to teaching cardiac pump dynamics and regulation to first-year medical students. I emphasize explicit presentation of the relation between the activity of the contractile machine in the myocytes to pump dynamics, pressure-volume relations, and cardiac output regulation, with matching oxygen supply to tissue demands serving as a focal point. Important ideas here are 1) the concept that regulation is at the cellular level of regulation; 2) that force and shortening properties of the cells are ultimately dependent on the number of cross bridges reacting with the thin filament and on the rate of cross-bridge cycling; 3) that the concepts of preload, afterload, and contractility originated in studies of muscle mechanics; 4) that there is a reserve of force-generating cross bridges, i.e., the myofilaments are not fully activated by [Ca.sup.2+] in the basal state, and that force-generating cross bridges can themselves activate the thin filament; and 5) that length dependence of myofilament [Ca.sup.2+] activation is important in the cellular basis of Starling's law of the heart. The elaboration of these processes serves to elucidate how these mechanisms play a role in coupling tissue oxygen demands to supply. AM.J. PHYSIOL. 277 (ADV. PHYSIOL. EDUC. 22): S155-S163, 1999. Key words: cardiac function; myocytes; cross bridges; calcium; pressure-volume relation

Park, J. H., N. Okayama, D. Gute, A. Krsmanovic, H. Battarbee, and J. S. Alexander. Hypoxia/aglycemia increases endothelial permeability: role of second messengers and cytoskeleton. Am. J. Physiol. 277 (Cell Physiol. 46): C1066-C1074, 1999.--The effects of hypoxia/aglycemia on microvascular endothelial permeability were evaluated, and the second messenger systems and the cytoskeletal-junctional protein alterations in this response were also examined. Monolayers of human dermal microvascular endothelial cells on microcarrier beads were exposed to either thioglycolic acid (5 mM, an [O.sub.2] chelator), glucose-free medium, or both stresses together. Permeability measurements were performed over a 90-min time course. Although neither hypoxia alone nor aglycemia alone increased endothelial permeability significantly, the combination of both increased significantly as early as 15 min. Intracellular [Ca.sup.2+] measurements with fura 2-AM showed that hypoxia/aglycemia treatment increased [Ca.sup.2+] influx. To determine the second messengers involved in increased permeability, monolayers were incubated for 30 min with the cytosolic [Ca.sup.2+] scavenger 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, 0.1 mM), a classical protein kinase C (PKC) blocker, Go-6976 (10 nM), a cGMP-dependent protein kinase (PKG) antagonist, KT-5823 (0.5 [micro]M), or the mitogen-activated protein (MAP) kinase inhibitor PD-98059 (20 [micro]M). Hypoxia/aglycemiamediated permeability changes were blocked by chelating cell [Ca.sup.2+], PKC blockade, PKG blockade, and by inhibiting p38 MAP kinase-1. Finally, changes in the binding of junctional proteins to the cytoskeleton under the same conditions were assessed. The concentrations of occludin and pan-reactive cadherin binding to the cytoskeleton were significantly decreased by only both stresses together. However, these effects were also blocked by pretreatment with TMB-8, Go-6976, KT-5823 (not in occludin), and PD-98059. These data suggest that hypoxia/aglycemia-mediated endothelial permeability may occur through PKC, PKG, MAP kinase, and [Ca.sup.2+] related to dissociation of cadherin-actin and occludin-actin junctional bonds. thioglycollate; oxygen; glucose; microvasculature; junction

Qu, Wei, Lee M. Graves, and Ronald G. Thurman. [PGE.sub.2] stimulates [O.sub.2] uptake in hepatic parenchymal cells: involvement of the cAMP-dependent protein kinase. Am. J. Physiol. 277 (Gastrointest. Liver Physiol. 40): G1048-G1054, 1999.--The aim of this study was to determine which [PGE.sub.2] receptors and signal transduction pathways are responsible for the stimulation of oxygen uptake in liver. Hepatic parenchymal cells isolated from female Sprague-Dawley rats were incubated either with [PGE.sub.2], 17-phenyl-omega-trinor [PGE.sub.2] (an [EP.sub.1]-specific agonist), or 11-deoxy [PGE.sub.1] (an [EP.sub.2]/[EP.sub.4]-specific agonist), and oxygen consumption was measured. Both [PGE.sub.2] and 11-deoxy [PGE.sub.1] stimulated oxygen consumption. However, an [EP.sub.1] agonist was without effect. Although [PGE.sub.2] elevated intracellular calcium, this occurred at concentrations ~500-fold lower than that required to stimulate oxygen uptake. [PGE.sub.2]-stimulated increases in cAMP formation correlated well with the increase in oxygen consumption. Dibutyryl cAMP also increased oxygen consumption. Furthermore, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide, a cell-permeable inhibitor of protein kinase A (PKA), reduced the stimulation of oxygen uptake by [PGE.sub.2]. Incubation of isolated parenchymal cell mitochondria with the purified catalytic subunit of PKA and ATP increased both state 3 rates of oxygen uptake and the respiratory control ratio by ~50%. Activation of these events was prevented by incubation with the PKA inhibitory peptide, PKI. These findings are consistent with the hypothesis that [PGE.sub.2] stimulates oxygen consumption via an [EP.sub.2] and/or [EP.sub.4] subclass of receptors through the actions of cAMP on a cAMP-dependent protein kinase. prostaglandin [E.sub.2]; protein kinase A; mitochondria

Coceani, F., Y.-A. Liu, E. Seidlitz, L. Kelsey, T. Kuwaki, C. Ackerley, and M. Yanagisawa. Endothelin A receptor is necessary for 02 constriction but not closure of ductus arteriosus. Am. J. Physiol. 277 (Heart Circ. Physiol. 46): H1521-H1531, 1999.--In vitro and in vivo techniques were developed with genetically modified mice to determine whether endothelin-1 (ET-1) functions as an [O.sub.2] mediator in closure of the ductus arteriosus (DA) at birth. Wild-type CD-1 and 129/SvEv mice with [ET.sub.A] receptor -/-, +/-, and +/+ genotypes were used. Isolated DA from term [ET.sub.A] +/+ fetuses contracted to [O.sub.2] (5-95%) and a thromboxane [A.sub.2] analog (ONO-11113, 0.1 [micro] M). Instead, ET-1 elicited a dual response with weak relaxation (0.1 nM) preceding contraction (1-100 nM). Indomethacin (2.8 [micro] M) was also a constrictor. [ET.sub.A] -/- DA, unlike [ET.sub.A] +/+ DA, contracted marginally to [O.sub.2] and ET-1 but responded to ONO-11113. [O.sub.2] contraction was also reduced in [ET.sub.A] +/- DA. In vivo, DA constricted equally in tracheotomized [ET.sub.A] -/- and [ET.sub.A] +/+ newborns. Conversely, no DA constriction was seen in hyperoxic [ET.sub.A] -/- fetuses in utero, although it occurred in [ET.sub.A] +/+ and +/- littermates. We conclude that ET-1 mediates the DA constrictor response to [O.sub.2.] Without ET-1, however, the vessel still closes postnatally, conceivably caused by the withdrawal of relaxing influence(s). oxygen; endothelin

Woodrum, David A., Colleen M. Brophy, Christopher J. Wingard, Arthur Beall, and Howard Rasmussen. Phosphorylation events associated with cyclic nucleotide-dependent inhibition of smooth muscle contraction. Am. J. Physiol. 277 (Heart Circ. Physiol. 46): H931-H939, 1999.--Activation of cyclic nucleotide-dependent signaling pathways leads to relaxation of bovine carotid artery smooth muscle contractions and is associated with increased phosphorylation of the small heat shock-related protein (HSP20). Previous reports have shown that human umbilical artery smooth muscle is uniquely resistant to cyclic nucleotide-dependent relaxation, and HSP20 is not phosphorylated. In this investigation, we determined the phosphorylation events associated with cyclic nucleotide-dependent inhibition of smooth muscle contraction. In carotid artery, activation of cyclic nucleotide-dependent signaling pathways inhibited contractile ressponses to serotonin but did not inhibit myosin light chain phosphorylation or oxygen consumption. The inhibition of contraction was associated with increases in HSP20 phosphorylation. In umbilical artery, activation of cyclic nucleotide-dependent signaling pathways did not inhibit serotonin-induced contraction or myosin light chain phosphorylation. The lack of contractile inhibition in umbilical artery was nc,t associated with significant increases in HSP20 phosphorylation. In conclusion, cyclic nucleotide-dependent contractile inhibition is independent of the inhibition of myosin light chain phosphorylation or oxygen consumption but does correlate with increased HSP20 phosphorylation. heat shock proteins; myosin light chains; oxygen consumption

Petrache, Irina, Mary E. Choi, Leo E. Otterbein, Beek Yoke Chin, Lin L. Mantell, Stuart Horowitz, and Augustine M. K. Choi. Mitogen-activated protein kinase pathway mediates hyperoxia-induced apoptosis in cultured macrophage cells. Am. J. Physiol. 277 (Lung Cell. Mol. Physiol. 21): L589-L595, 1999.--We have previously demonstrated that the lungs of mice can exhibit increased programmed cell death or apoptosis after hyperoxic exposure in vivo. In this report, we show that hyperoxic exposure in vitro can also induce apoptosis in cultured murine macrophage cells (RAW 264.7) as assessed by DNA-laddering, terminal deoxynucleo-tidyltransferase dUTP nick end-labeling, and nucleosomal assays. To further delineate the signaling pathway of hyperoxia-induced apoptosis in RAW 264.7 macrophages, we first show that hyperoxia can activate the mitogen-activated protein kinase (MAPK) pathway, the extracellular signal-regulated kinases (ERKs) p42/p44, in a time-dependent manner as assessed by increased phosphorylation of ERK1/ERK2 by Western blot analyses. Neither the c-Jun [NH.sub.2]-terminal kinase/stress-activated protein kinase nor the p38 MAPK was activated by hyperoxia in these cells. Chemical or genetic inhibition of the ERK p42/p44 MAPK pathway by PD-98059, a selective inhibitor of MAPK kinase, and dominant negative mutants of ERK, respectively, attenuated hyperoxia-induced apoptosis as assessed by DNA laddering and nucleosomal ELISAs. Taken together, our data suggest that hyperoxia can induce apoptosis in cultured murine macrophages and that the MAPK pathway mediates hyperoxia-induced apoptosis. programmed cell death; oxygen; signal transduction; extracellular signal-regulated kinase; cell death

Research was conducted to examine the induction of thioredoxin (TRX) and thioredoxin reductase gene expression in lungs of newborn primates using oxygen. It was observed that lung TRX, a potent protein disulfide oxidoreductase essential in antioxidant defense and cell growth and signal transduction processes regulation, and its reductase are upregulated at birth by oxygen. Results indicate an important role for the proteins during the transition from anaerobic fetal life to oxygen breathing at birth.