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In this study, the role of nitric oxide (NO) in regulation of the pulmocutaneous vasculature of the toad, Bufo marinus was investigated. In vitro myography demonstrated the presence of a neural NO signaling mechanism in both arteries. Vasodilation induced by nicotine was inhibited by the soluble guanylyl cyclase (GC) inhibitor, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one, and the NO synthase (NOS) inhibitor, [N.sup.[omega]]-nitro-L-arginine (L-NNA). Removal of the endothelium had no significant effect on the vasodilation. Furthermore, pretreatment with [N.sup.5]-(1-imino-3-butenyl)-L-ornithine (vinyl-L-NIO), a more specific inhibitor of neural NOS, caused a significant decrease in the nicotine-induced dilation. In the pulmonary artery only, a combination of L-NNA and the calcitonin gene-related peptide (CGRP) receptor antagonist, [CGRP.sub.(8-37)], completely blocked the nicotine-induced dilation. In both arteries, the vasodilation was also significantly decreased by glibenclamide, an ATP-sensitive [K.sup.+] ([K.sup.+]ATP) channel inhibitor. Levcromakalim, a [K.sup.+]ATP channel opener, caused a dilation that was blocked by glibenclamide in both arteries. In the pulmonary artery, NO donormediated dilation was significantly decreased by pretreatment with glibenclamide. The physiological data were supported by NADPH-diaphorase histochemistry and immunohistochemistry, which demonstrated NOS in perivascular nerve fibers but not the endothelium of the arteries. These results indicate that the pulmonary and cutaneous arteries of B. marinus are regulated by NO from nitrergic nerves rather than NO released from the endothelium. The nitrergic vasodilation in the arteries appears to be caused, in part, via activation of [K.sup.+]ATP channels. Thus, NO could play an important role in determining pulmocutaneous blood flow and the magnitude of cardiac shunting. endothelium; nitric oxide synthase; autonomic nervous system; amphibian; vasodilation

To determine whether conduit artery size affects functional responses, we compared the magnitude, time course, and eliciting shear rate stimulus for flow-mediated dilation (FMD) in healthy men (n = 20; 31 [+ or -] 7 yr). Upper limb (brachial and radial) and lower limb (common and superficial femoral) FMD responses were simultaneously assessed, whereas popliteal responses were measured in the same subjects during a separate visit. Glyceryl trinitrate (GTN)-mediated responses were similarly examined. Edge detection and wall tracking of high-resolution B-mode arterial ultrasound images, combined with synchronized Doppler waveform envelope analysis, were used to calculate conduit artery diameter, blood flow, and shear rate continuously across the cardiac cycle. Baseline artery size correlated inversely with the FMD response (r = -0.57, P < 0.001). Within-artery comparisons revealed a significant inverse correlation between artery size and FMD% for the radial (r = -0.66, P = 0.001), brachial (r = -0.55, P = 0.01), and popliteal artery (r = -0.48, P = 0.03), but not for the superficial and common femoral artery. Normalization of FMD responses for differences in eliciting shear rate did not abolish the between-artery relationship for artery function and size (r = -0.48, P < 0.001), suggesting that differences between artery function responses were not entirely due to size-related differences in shear rate. This was reinforced by a significant between-artery correlation for GTN responses and baseline artery size (r = -0.74, P < 0.001). In summary, systematic differences exist in vascular function responses of conduit arteries that differ in size. This raises the possibility that differences in artery size within or between individuals may influence functional responses. flow-mediated dilation; nitroglycerine; arterial diameter; high-resolution ultrasound; Doppler

An artery ring springs open into a sector after a radial cut. The opening angle characterizes the residual strain in the unloaded state, which is fundamental in understanding stress and strain in the vessel wall. A recent study revealed that the opening angle decreases with time if the artery is cut from the loaded state, while it increases if the cut is made from the no-load state due to viscoelasticity. In both cases, the opening angle approaches the same value in 3 h. This implies that the characteristic relaxation time is about 10,000 s. Here, the creep function of a generalized Maxwell model (a spring in series with six Voigt bodies) is used to predict the temporal change of opening angle in multiple time scales. It is demonstrated that the theoretical model captures the salient features of the experimental results. The proposed creep function may be extended to study the viscoelastic response of blood vessels under various loading conditions. Keywords: relaxation, creep, viscoelastic, blood vessel

Flow-mediated dilation (FMD) has become a commonly applied approach for the assessment of vascular function and health, but methods used to calculate FMD differ between studies. For example, the baseline diameter used as a benchmark is sometimes assessed before cuff inflation, whereas others use the diameter during cuff inflation. Therefore, we compared the brachial artery diameter before and during cuff inflation and calculated the resulting FMD in healthy children (n = 45; 10 [+ or -] 1 yr), adults (n = 31; 28 [+ or -] 6 yr), and older subjects (n = 22; 58 [+ or -] 5 yr). Brachial artery FMD was examined after 5 min of distal ischemia. Diameter was determined from either 30 s before cuff inflation or from the last 30 s during cuff inflation. Edge detection and wall tracking of high resolution B-mode arterial ultrasound images was used to calculate conduit artery diameter. Brachial artery diameter during cuff inflation was significantly larger than before inflation in children (P = 0.02) and adults (P < 0.001) but not in older subjects (P = 0.59). Accordingly, FMD values significantly differed in children (11.2 [+ or -] 5.1% vs. 9.4 [+ or -] 5.2%; P = 0.02) and adults (7.3 [+ or -] 3.2% vs. 4.6 [+ or -] 3.3%; P < 0.001) but not in older subjects (6.3 [+ or -]3.4% vs. 6.0 [+ or -] 4.2%; P = 0.77). When the diameter before cuff inflation was used, an age-dependent decline was evident in FMD, whereas FMD calculated using the diameter during inflation was associated with higher FMD values in older than younger adults. In summary, the inflation of the cuff significantly increases brachial artery diameter, which results in a lower FMD response. This effect was found to be age dependent, which emphasizes the importance of using appropriate methodology to calculate the FMD. methodology

This study determined if altered vascular prostacyclin ([PGI.sub.2]) and/or thromboxane [A.sub.2] (Tx[A.sub.2]) production with reduced [Po.sub.2] contributes to impaired hypoxic dilation of skeletal muscle resistance arterioles of obese Zucker rats (OZRs) versus lean Zucker rats (LZRs). Mechanical responses were assessed in isolated gracilis muscle arterioles following reductions in [Po.sub.2] under control conditions and following pharmacological interventions inhibiting arachidonic acid metabolism and nitric oxide synthase and alleviating elevated vascular oxidant stress. The production of arachidonic acid metabolites was assessed using pooled arteries from OZRs and LZRs in response to reduced [Po.sub.2]. Hypoxic dilation, endothelium-dependent in both strains, was attenuated in OZRs versus LZRs. Nitric oxide synthase inhibition had no significant impact on hypoxic dilation in either strain. Cyclooxygenase inhibition dramatically reduced hypoxic dilation in LZRs and abolished responses in OZRs. Treatment of arterioles from OZRs with polyethylene glycol-superoxide dismutase improved hypoxic dilation, and this improvement was entirely cyclooxygenase dependent. Vascular [PGI.sub.2] production with reduced [Po.sub.2] was similar between strains, although Tx[A.sub.2] production was increased in OZRs, a difference that was attenuated by treatment of vessels from OZRs with polyethylene glycol-superoxide dismutase. Both blockade of [PGH.sub.2]/Tx[A.sub.2] receptors and inhibition of thromboxane synthase increased hypoxic dilation in OZR arterioles. These results suggest that a contributing mechanism underlying impaired hypoxic dilation of skeletal muscle arterioles of OZRs may be an increased vascular production of Tx[A.sub.2], which competes against the vasodilator influences of [PGI.sub.2]. These results also suggest that the elevated vascular oxidant stress inherent in metabolic syndrome may contribute to the increased vascular Tx[A.sub.2] production and may blunt vascular sensitivity to [PGI.sub.2]. skeletal muscle microcirculation; endothelium-dependent dilation; vascular reactivity; rodent models of obesity

With little known regarding sex and limb heterogeneity, we investigated vascular reactivity and ischemic reperfusion (IR) in the upper and lower extremities of 15 healthy men (26 [+ or -] 2 yr) and women (23 [+ or -] 1 yr). Doppler ultrasound was used to evaluate IR and flow-mediated dilation (FMD) after suprasystolic cuff occlusion in both the arm [brachial artery (BA)] and the leg [popliteal artery (PA)]. Cumulative IR [area under the curve (AUC)], normalized for muscle mass, revealed no sex-related differences in either limb (forearm: men 38 [+ or -] 3 and women 44 [+ or -] 4 ml/100 g; lower leg: men 12 [+ or -] 2 and women 14 [+ or -] 2 ml/100 g), while both groups revealed a greater IR per unit of arm muscle mass (AUC) compared with the lower leg (P < 0.05). The BA and PA were smaller in women (BA 0.31 [+ or -] 0.1, PA 0.47 [+ or -] 0.1 cm) than in men (BA 0.41 [+ or -] 0.1, PA 0.6 [+ or -] 0.2 cm). Absolute FMD/shear rate revealed attenuated vascular function in the PA of the women [women 3.3 [+ or -] 0.6, men 5.0 [+ or -] 0.8 (all x [10.sup.-6]) cm/[s.sup.-1] and no sex difference in the BA [women 1.2 [+ or -] 0.2, men 1.6 [+ or -] 0.1 (all x [10.sup.-6]) cm/[s.sup.-1] x s]. In both sexes the PA demonstrated greater vascular reactivity than the BA. Thus vascular reactivity in healthy young people is greater in the legs, regardless of sex, and women have vascular function similar to men in the upper extremities but appear to have poorer vascular function normalized for shear rate in the lower extremities. vasodilation; vascular function; hyperemia; females

Nitric oxide (NO) has been shown to be the endothelium-derived relaxing factor (EDRF), and its impairment contributes to a variety of cardiovascular disorders. Recently, it has been recognized that nitrite can be an important source of NO; however, questions remain regarding the activity and mechanisms of nitrite bioactivation in vessels and its physiological importance. Therefore, we investigated the effects of nitrite on in vivo hemodynamics in rats and in vitro vasorelaxation in isolated rat aorta under aerobic conditions. Studies were performed to determine the mechanisms by which nitrite is converted to NO. In anesthetized rats, nitrite dose dependently decreased both systolic and diastolic blood pressure with a threshold dose of l0 [micro]M. Similarly, nitrite (10 [micro]M-2 mM) caused vasorelaxation of aortic rings, and NO was shown to be the intermediate factor responsible for this activity. With the use of electrochemical as well as electron paramagnetic resonance (EPR) spectroscopy techniques NO generation was measured from isolated aortic vessels following nitrite treatment. Reduction of nitrite to NO was blocked by heating the vessel, suggesting that an enzymatic process is involved. Organ chamber experiments demonstrated that aortic relaxation induced by nitrite could be blocked by both hemoglobin and soluble guanylyl cyclase (sGC) inhibitor 1H[1,2,4] oxadiazolo[4,3-a]quinoxaline-l-one (ODQ). In addition, both electrochemical and EPR spin-trapping measurements showed that ODQ inhibits nitrite-mediated NO production. These findings thus suggest that nitrite can be a precursor of EDRF and that sGC or other heme proteins inhibited by ODQ catalyze the reduction of nitrite to NO. soluble guanylate cyclase; aerobic nitrite reduction; vasorelaxation; blood pressure; heme proteins

We previously showed a prolonged inhibition of current-induced vasodilation (CIV) after a single oral high dose of aspirin. In this study, we tested the hypothesis of platelet involvement in CIV. Nine healthy volunteers took 75 mg aspirin/day, 98 mg of clopidogrel bisulfate/day, or placebo for 4 days. CIV was induced by two consecutive 1-min anodal current applications (0.08 mA/[cm.sup.2]) through deionized water with a 10-min interval. CIV was measured with laser Doppler flowmetry and expressed as a percentage of baseline cutaneous vascular conductance: %[C.sub.b]. In a second experiment in 10 volunteers, aspirin and placebo were given as in experiment 1, but a 26-h delay from the last aspirin intake elapsed before ACh iontophoresis and postocclusive hyperemia were studied in parallel to CIV. In experiment 1, the means [+ or -] SE amplitude of CIV was 822 [+ or -] 314, 313 [+ or -] 144, and 746 [+ or -] 397% [C.sub.b] with placebo, aspirin (P < 0.05 from placebo and clopidogrel), and clopidogrel (NS from placebo), respectively. In experiment 2, CIV impairment with aspirin was confirmed: CIV amplitudes were 300 [+ or -] 99, and 916 [+ or -] 528%[C.sub.b] under aspirin and placebo, respectively (P < 0.05), whereas vasodilation to ACh iontophoresis (322 [+ or -] 74 and 365 [+ or -] 104%Cb) and peak postocclusive hyperemia (491 [+ or -] 137 and 661 [+ or -] 248%Cb) were not different between aspirin and placebo, respectively. Low-dose aspirin, even 26 h after oral administration, impairs CIV, while ACh-mediated vasodilation and postocclusive hyperemia are preserved. If platelets are involved in the neurovascular mechanism triggered by galvanic current application in humans, it is likely to occur through the cyclooxygenase but not the ADP pathway. microcirculation; axon reflex; platelets; skin

We previously demonstrated a role for voltage-dependent [K.sup.+] ([K.sub.v]) channels in coronary vasodilation elicited by myocardial metabolism and exogenous [H.sub.2][0.sub.2], as responses were attenuated by the [K.sub.v] channel blocker 4-aminopyridine (4-AP). Here we tested the hypothesis that [K.sub.v] channels participate in coronary reactive hyperemia and examined the role of [K.sub.v] channels in responses to nitric oxide (NO) and adenosine, two putative mediators. Reactive hyperemia (30-s occlusion) was measured in open-chest dogs before and during 4-AP treatment [intracoronary (ic), plasma concentration 0.3 mM]. 4-AP reduced baseline flow 34 [+ or -] 5% and inhibited hyperemic volume 32 [+ or -] 5%. Administration of 8-phenyltheophylline (8-PT; 0.3 mM ic or 5 mg/kg iv) or [N.sup.G]-nitro-L-arginine methyl ester (L-NAME; 1 mg/min ic) inhibited early and late portions of hyperemic flow, supporting roles for adenosine and NO. 4-AP further inhibited hyperemia in the presence of 8-PT or L-NAME. Adenosine-induced blood flow responses were attenuated by 4-AP (52 [+ or -] 6% block at 9 [micro]g/min). Dilation of arterioles to adenosine was attenuated by 0.3 mM 4-AP and 1 [micro]M correolide, a selective [K.sub.v]1 antagonist (76 [+ or -] 7% and 47 [+ or -] 2% block, respectively, at 1 [micro]M). Dilation in response to sodium nitroprusside, an NO donor, was attenuated by 4-AP in vivo (41 [+ or -] 6% block at 10 [micro]g/min) and by correolide in vitro (29 [+ or -] 4% block at 1 [micro]M). [K.sub.v] current in smooth muscle cells was inhibited by 4-AP (I[C.sub.50] 1.1 [+ or -] 0.1 mM) and virtually eliminated by correolide. Expression of mRNA for [K.sub.v]l family members was detected in coronary arteries. Our data indicate that [K.sub.v] channels play an important role in regulating resting coronary blood flow, determining duration of reactive hyperemia, and mediating adenosine- and NO-induced vasodilation. ischemic vasodilation; adenosine; 4-aminopyridine; delayed rectifier potassium channel; vascular smooth muscle

The aim of the present study was to provide a mechanistic insight into how 20-hydroxyeicosatetraenoic acid (20-HETE) relaxes distal human pulmonary arteries (HPAs). This compound is produced by to-hydroxylase from free arachidonic acid. Tension measurements, performed on either fresh or 1 day-cultured pulmonary arteries, revealed that the contractile responses to 1 [micro]M 5-hydroxytryptamine were largely relaxed by 20-HETE in a concentration-dependent manner (0.01-10 [micro]M). Iberiotoxin pretreatments (10 nM) partially decreased 20-HETE-induced relaxations. However, 10 [micro]M indomethacin and 3 [micro]M SC-560 pretreatments significantly reduced the relaxations to 20-HETE in these tissues. The relaxing responses induced by the eicosanoid were likely related to a reduced [Ca.sup.2+] sensitivity of the myofilaments since free [Ca.sup.2+] concentration ([[Ca.sup.2+]])-response curves performed on [beta]-escin-permeabilized cultured explants were shifted toward higher [[Ca.sup.2+]]. 20-HETE also abolished the tonic responses induced by phorbol-ester-dibutyrate (a PKC-sensitizing agent). Western blot analyses, using two specific primary antibodies against the PKC-potentiated inhibitory protein CPI-17 and its PKC-dependent phosphorylated isoform pCPI- 17, confirmed that 20-HETE interferes with this intracellular process. We also investigated the effect of 20-HETE on the activation of Rho-kinase pathway-induced [Ca.sup.2+] sensitivity. The data demonstrated that 20-HETE decreased U46619-induced [Ca.sup.2+] sensitivity on arteries. Hence, this observation was correlated with an increased staining of [p116.sup.Rip], a RhoA-binding protein. Together, these results strongly suggest that the 20-hydroxyarachidonic acid derivative is a potent modulator of tone in HPAs in vitro. 20-hydroxyeicosatetraenoic acid; calcium sensitivity; tension measurement

The objectives of this study were to determine whether placental growth factor (P1GF) exerts a vasodilatory effect on rat uterine vessels (arcuate arteries and veins) and to examine regional differences in reactivity by comparing these responses to those of comparably sized mesenteric vessels. We also sought to examine and compare its effects on human uterine and subcutaneous vessels. All vessels were studied in vitro, under pressurized (rat) or isometric wire-mounted (human) conditions, and exposed to a range of P1GF concentrations. Inhibitors of nitric oxide and prostaglandin synthesis were included in an effort to understand the causal mechanism(s). In rat uterine arteries, the effects of receptor inhibition and activation using selective ligands for VEGFR-1 (PIGF) vs. VEGFR-2 (VEGF-E) were determined, and real-time RT-PCR was performed to evaluate the effect of pregnancy on relative abundance of VEGFR-1 and VEGFR-2 message in the vascular wall. P1GF was a potent vasodilator of all vessels studied, with greatest sensitivity observed in rat uterine arteries. Pregnancy significantly augmented dilator sensitivity to P1GF, and this effect was associated with selective upregulation of VEGFR-1 message in the pregnant state. The contribution of nitric oxide was appreciable in rat and human uterine arteries, with lesser effects in rat uterine veins and mesenteric arteries, and with no observable effect in human subcutaneous vessels. Based on these results, we conclude that P1GF is a potent vasodilator of several vessel types in both humans and rats. Its potency and mechanism vary with physiological state and vessel location and are mediated solely by the VEGFR-1 receptor subtype. Gestational changes in the uterine circulation suggest that this factor may play a role in modulating uterine vascular remodeling and blood flow during the pregnant state. vascular endothelial growth factor; nitric oxide; uterine circulation; rat; human resistance arteries; vascular endothelial growth factor receptor-1; fms-like tyrosine kinase-1

Arachidonic acid (AA) causes endothelium-dependent smooth muscle hyperpolarizations and relaxations that are mediated by a 15-lipoxygenase-I (15-LO-I) metabolite, 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA). We propose that AA is metabolized sequentially by 15-LO-I and hydroperoxide isomerase to an unidentified hydroxyepoxyeicosatrienoic acid (HEETA), which is hydrolyzed by a soluble epoxide hydrolase (sEH) to 11,12,15-THETA. After incubation of aorta with [sup.4]C-labeled AA, metabolites were extracted and the HEETAs were resolved by performing HPLC. Mass spectrometric analyses identified 15-Hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA). Incubation of aortic incubates with methanol and acetic acid trapped the acidsensitive 15-H-11,12-EETA as methoxydihydroxyeicosatrienoic acids (MDHEs) (367 m/z, M-H). Pretreatment of the aortic tissue with the sEH inhibitor 12-(3-adamantan-l-yl-ureido)-dodecanoic acid (AUDA; [10.sup.-6] M) increased the formation of 15-H-11,12-EETA, measured as MDHEs. Thus 15-H-11,12-EETA is an acid- and sEH-sensitive precursor of 11,12,15-THETA. Aortic homogenates and endothelial cells contain a 57-kDa protein corresponding to the rabbit sEH. In preconstricted aortic rings, AA ([10.sup.-7]-[10.sup.-4] M) and acetylcholine ([10.sup.-9]-[10.sup.-6] M) caused concentration-related relaxations that were enhanced by pretreatment with AUDA. These enhanced relaxations were inhibited by increasing extracellular [[K.sup.+]] from 4.8 to 20 mM. AA (3 x [10.sup.-6] M) induced cell membrane hyperpolarization (from -31.0 [+ or -] 1 to -46.8 [+ or -] 2 mV) in aortic strips with an intact endotfielium, which was enhanced by AUDA. These results indicate that 15-H-11,12-EETA is produced by the aorta, hydrolyzed by sEH to 11,12,15-THETA, and mediates relaxations by membrane hyperpolarization. 15-H-11,12-EETA represents an endothelium-derived hyperpolarizing factor. arachidonic acid; endothelial cells; endothelium-derived hyperpolarizing factor; 15-lipoxygenase

Calcitonin gene-related peptide (CGRP), a potent vasodilator released from capsaicin-sensitive C-fiber and A[delta]-fiber sensory nerves, has been suggested to play a beneficial role in myocardial ischemia-reperfusion (I/R) injury. Because most previous studies showing a cardioprotective role of CGRP employed pharmacological experiments, the purpose of this study was to utilize a genetic approach by using mice with a targeted deletion of the [alpha]-CGRP gene to determine whether this neuropeptide had a modulatory function on the severity of I/R injury. To accomplish this goal, isolated, perfused hearts from [alpha]-CGRP knockout (KO) and wild-type (WT) mice were subjected to 30 min of ischemia followed by 5, 15, and 30 min of reperfusion. Cardiac functional parameters, including coronary flow rates, left ventricular developed pressure, maximum rates of pressure development, and left ventficular end-diastolic pressure, were measured before and after I/R injury, as were levels of creatine kinase, to assess myocardial damage, and malonaldehyde, to assess oxidative stress. Following I/R injury, cardiac performance was significantly reduced in the hearts from the [alpha]-CGRP KO mice compared with their WT counterparts. The marked reduction in myocardial function in the [alpha]-CGRP KO hearts compared with WT hearts after I/R injury was associated with a significant elevation in creatine kinase release into the perfusates and malonaldehyde production in the cardiac tissue. Therefore, these data indicate that, in this in vitro setting, deletion of [alpha]-CGRP makes the heart more vulnerable to I/R injury, possibly due, at least in part, to increased oxidative stress. genetically modified mice; cardiac; isolated perfused heart preparations; sensory nervous system

This study examines in endothelium-denuded bovine pulmonary arteries the effects of increasing heme oxygenase-I (HO-1) activity on relaxation and soluble guanylate cyclase (sGC) activation by nitric oxide (NO). A 24-h organ culture with 0.1 mM cobalt chloride (COC12) or 30 [micro]M Co-protoporphyrin IX was developed as a method of increasing HO-1 expression. These treatments increased HO-1 expression and HO activity by approximately two- to fourfold and lowered heme levels by 40-45%. Induction of HO-1 was associated with an attenuation of pulmonary arterial relaxation to the NO-donor spermine-NONOate. The presence of a HO-1 inhibitor 30 [micro]M chromium mesoporphyrin during the 24-h organ culture (but not acute treatment with this agent) reversed the attenuation of relaxation to NO seen in arteries co-cultured with agents that increased HO-1. Relaxation to isoproterenol, which is thought to be mediated through cAMP, was not altered in arteries with increased HO-1. Inducers of HO-1 did not appear to alter basal sGC activity in arterial homogenates or expression of the [[beta].sub.1]-subunit of sGC. However, the increase in activity seen in the presence of 1 [micro]M spermine-NONOate was attenuated in homogenates obtained from arteries with increased HO-1. Since arteries with increased HO-I had decreased levels of superoxide detected by the chemiluminescence of 5 [micro]M lucigenin, superoxide did not appear to be mediating the attenuation of relaxation to NO. These data suggest that increasing HO-1 activity depletes heme, and this is associated with an attenuation of pulmonary artery relaxation and sGC activation responses to NO. cGMP; cobalt protoporphyrin; chromium mesoporphyrin; superoxide

Although the hydraulic work generated by the left ventricle (LV) is not disputed, how the work was dissipated through the systemic circulation is still subject to interpretation. Recently, we proposed that the systemic circulation should be considered as waves and a reservoir system (Wk). By combining the arterial and venous reservoirs, the systemic vascular resistance can be viewed as a series of resistors, which in sequence are the large-artery resistance, arterial reservoir resistance, the microcirculatory resistance, venous reservoir resistance, and large-vein resistance, and propelling blood through these resistance elements represents resistive losses. We then studied the changes in the fraction of the work consumed by each element when infusing methoxamine (MTX), a vasoconstrictor, and sodium nitroprusside (NP), a vasodilator. Results show that, under control condition, ~50% of the LV stroke work was dissipated through arterial reservoir resistance (NP, ~36%; MTX, ~27%), another ~25% was dissipated by the microcirculation (NP, ~20%; MTX, ~66%), and ~20% of work by the large-artery resistances (NP, ~37%; MTX, ~6%). The energy dissipated by the venous resistances was small and had limited variation with NP and MTX, where the large-vein and venous reservoir resistances shared ~1 and ~3% of LV stroke work, respectively. Approximately 60% of LV stroke work is stored as the potential energy during systole under control, and the ratio decreases to ~45% with NP and ~80% with MTX. left ventricle circulatory coupling; systemic vascular resistance; arterial and venous reservoirs

Ghrelin infusion improves cardiac function in patients suffering from cardiac failure, and bolus administration of ghrelin increases cardiac output in healthy subjects. The cardiovascular effects of more continuous intravenous ghrelin exposure remain to be studied. We therefore studied the cardiovascular effects of a constant infusion of human ghrelin at a rate of 5 pmol/kg per minute for 180 min. Fifteen healthy, young (aged 23.2 [+ or -] 0.5 yr), normal-weight (23.0 [+ or -] 0.4 kg/m2) men volunteered in a randomized double-blind, placebo-controlled crossover study. With the subjects remaining fasting, peak myocardial systolic velocity S', tissue tracking TT, left ventricular ejection fraction EF, and endothelium-dependent flow-mediated vasodilatation were measured. Ghrelin infusion increased S' 9% (P = 0.002) and TT 10% (P < 0.001), whereas EF, resting blood flow velocity, and endothelium-dependent flow-mediated vasodilatation did not change (P = 0.13). This was associated with a peak in serum growth hormone after 60 min of infusion (37.77 [+ or -] 5.27 ng/ml, P < 0.001), a doubling of free fatty acid levels (P = 0.001), and a 1.6-fold increase in cortisol levels (P < 0.05), whereas glucose and catecholamine levels were constant. In conclusion, supraphysiological levels of ghrelin stimulate left ventricular function in terms of S' and TT in healthy young normal-weight men without changing resting blood flow velocity and endothelium-dependent flow-mediated vasodilatation. The effects did not translate into detectable increments in EF. left ventricular function; tissue Doppler imaging; tissue tracking; endothelium-dependent flow-mediated vasodilatation

Nitrite reacts with deoxyhemoglobin to generate nitric oxide (NO). This reaction has been proposed to contribute to nitrite-dependent vasodilation in vivo and potentially regulate physiological hypoxic vasodilation. Paradoxically, while deoxyhemoglobin can generate NO via nitrite reduction, both oxyhemoglobin and deoxyhemoglobin potently scavenge NO. Furthermore, at the very low [O.sub.2] tensions required to deoxygenate cell-free hemoglobin solutions in aortic ring bioassays, surprisingly low doses of nitrite can be reduced to NO directly by the blood vessel, independent of the presence of hemoglobin; this makes assessments of the role of hemoglobin in the bioactivation of nitrite difficult to characterize in these systems. Therefore, to study the [O.sub.2] dependence and ability of deoxhemoglobin to generate vasodilatory NO from nitrite, we performed full factorial experiments of oxyhemoglobin, deoxyhemoglobin, and nitrite and found a highly significant interaction between hemoglobin deoxygenation and nitrite-dependent vasodilation (P [less than or equal to] 0.0002). Furthermore, we compared the effect of hemoglobin oxygenation on authentic NO-dependent vasodilation using a NONOate NO donor and found that there was no such interaction, i.e., both oxyhemoglobin and deoxyhemoglobin inhibited NO-mediated vasodilation. Finally, we showed that another NO scavenger, 2-carboxyphenyl-4,4-5,5-tetramethylimidazoline-l-oxyl-3-oxide, inhibits nitritedependent vasodilation under normoxia and hypoxia, illustrating the uniqueness of the interaction of nitrite with deoxyhemoglobin. While both oxyhemoglobin and deoxyhemoglobin potently inhibit NO, deoxyhemoglobin exhibits unique functional duality as an NO scavenger and nitrite-dependent NO generator, suggesting a model in which intravascular NO homeostasis is regulated by a balance between NO scavenging and NO generation that is dynamically regulated by hemoglobin's [O.sub.2] fractional saturation and allosteric nitrite reductase activity. nitric oxide; hypoxia; blood flow

Endothelial (eNOS) and neuronal nitric oxide synthase (nNOS) are implicated as important contributors to cerebral vascular regulation through nitric oxide (NO). However, direct in vivo measurements of NO in the brain have not been used to dissect their relative roles, particularly as related to oxygenation of brain tissue. We found that, in vivo, rat cerebral arterioles had increased NO concentration ([NO]) and diameter at reduced periarteriolar oxygen tension ([Po.sub.2]) when either bath oxygen tension or arterial pressure was decreased. Using these protocols with highly selective blockade of nNOS, we tested the hypothesis that brain tissue nNOS could donate NO to the arterioles at rest and during periods of reduced perivascular oxygen tension, such as during hypotension or reduced local availability of oxygen. The decline in periarteriolar [Po.sub.2] by bath manipulation increased [NO] and vessel diameter comparable with responses at similarly decreased [Po.sub.2] during hypotension. To determine whether the nNOS provided much of the vascular wall NO, nNOS was locally suppressed with the highly selective inhibitor N-(4S)-(4-amino-5-[aminoethyl]aminopentyl)-[N.sup.']-nitroguanidine. After blockade, resting [NO], [Po.sub.2], and diameters decreased, and the increase in [NO] during reduced [Po.sub.2] or hypotension was completely absent. However, flow-mediated dilation during occlusion of a collateral arteriole did remain intact after nNOS blockade and the vessel wall [NO] increased to ~80% of normal. Therefore, nNOS predominantly increased NO during decreased periarteriolar oxygen tension, such as that during hypotension, but eNOS was the dominant source of NO for flow shear mechanisms. nitric oxide; brain; arterioles; in vivo; microelectrode; neuronal nitric oxide synthase

Loria A, Reverte V, Salazar F, Saez F, Llinas MT, Salazar FJ. Changes in renal hemodynamics and excretory function induced by a reduction of ANG II effects during renal development. Am J Physiol Regul Integr Comp Physiol 293' R695-R700, 2007. First published May 9, 2007; doi:10.1152/ajpregu.00191.2007.--The aim was to evaluate whether blockade of ANG II effects during renal development modifies the renal response to an increment of plasma amino acid concentration. It was also examined in anesthetized rats whether the reduction of the renal ability to eliminate an acute volume expansion (VE), elicited by blockade of ANG II during renal development, is sex and/or age dependent. Newborn Sprague-Dawley rats were treated with vehicle or an A[T.sub.1]-receptor antagonist (ARA) during postnatal nephrogenesis. Amino acid infusion induced increments (P < 0.05) of glomerular filtration rate (31 [+ or -] 6%) and renal plasma flow (26 [+ or -] 5%) in male but not in female vehicle-treated rats. Natriuretic and diuretic responses to amino acid infusion were similar in male and female vehicle-treated rats. These renal hemodynamics and excretory responses to amino acid infusion were abolished in ARA-treated rats. Renal responses to VE were evaluated at 3-4 and 9-10 mo of age in vehicle and ARA-treated rats. VE-induced natriuresis and diuresis were reduced by more than 38% (P < 0.05) in 3- to 4-mo-old male and female ARA-treated rats. An age-dependent reduction (P < 0.05) in the renal ability to eliminate VE was found in male but not in female rats treated with ARA. Our results demonstrate that the renal effects induced by an increment in amino acids are abolished when ANG II effects have been reduced during nephrogenesis. In addition, this reduction of ANG II effects elicits an impairment of the renal ability to eliminate an acute VE in males and females, which is aggravated by age only in male rats. amino acid; filtration rate; nephrogenesis; renal vasodilatation; volume expansion

Ishii H, Niioka T, Watanabe H, Izumi H. Inhibitory effects of excess sympathetic activity on parasympathetic vasodilation in the rat masseter muscle. Am J Physiol Regul Integr Comp Physiol 293: R729-R736, 2007. First published May 30, 2007; doi: 10.1152/ajpregu.00866.2006.--The present study was designed to examine the effect of sympathetic tonic activity on parasympathetic vasodilation evoked by the trigeminal-mediated reflex in the masseter muscle in urethane-anesthetized rats. Sectioning of the superior cervical sympathetic trunk (CST) ipsilaterally increased the basal level of blood flow in the masseter muscle (MBF). Electrical stimulation of the peripheral cut end of the CST for 2 min using 2-ms pulses ipsilaterally decreased in a dependent manner the intensity (0.5-10 V) and frequency (0.1-5 Hz) of the MBF. The CST stimulation for 2 min at superior cervical sympathetic trunk; vasoconstrictor fiber; adrenoceptors; trigeminal-mediated reflex; jaw muscle

Nitric oxide (NO) plays a key role in regulating vascular tone. Mice overexpressing endothelial NO synthase [eNOS-transgenic (Tg)] have a 20% lower systemic vascular resistance (SVR) than wild-type (WT) mice. However, because eNOS enzyme activity is 10 times higher in tissue homogenates from eNOS-Tg mice, this in vivo effect is relatively small. We hypothesized that the effect of eNOS overexpression is attenuated by alterations in NO signaling and/or altered contribution of other vasoregulatory pathways. In isoflurane-anesthetized open-chest mice, eNOS inhibition produced a significantly greater increase in SVR in eNOS-Tg mice compared with WT mice, consistent with increased NO synthesis. Vasodilation to sodium nitroprusside (SNP) was reduced, whereas the vasodilator responses to phosphodiesterase-5 blockade and 8-bromo-cGMP (8-Br-cGMP) were maintained in eNOS-Tg compared with WT mice, indicating blunted responsiveness of guanylyl cyclase to NO, which was supported by reduced guanylyl cyclase activity. There was no evidence of eNOS uncoupling, because scavenging of reactive oxygen species (ROS) produced even less vasodilation in eNOS-Tg mice, whereas after eNOS inhibition the vasodilator response to ROS scavenging was similar in WT and eNOS-Tg mice. Interestingly, inhibition of other modulators of vascular tone [including cyclooxygenase, cytochrome P-450 2C9, endothelin, adenosine, and Ca-activated [K.sup.+] channels] did not significantly affect SVR in either eNOS-Tg or WT mice, whereas the marked vasoconstrictor responses to ATP-sensitive [K.sup.+] and voltage-dependent [K.sup.+] channel blockade were similar in WT and eNOS-Tg mice. In conclusion, the vasodilator effects of eNOS overexpression are attenuated by a blunted NO responsiveness, likely at the level of guanylyl cyclase, without evidence of eNOS uncoupling or adaptations in other vasoregulatory pathways. nitric oxide signaling; vasodilation; reactive oxygen species; redundancy

Full expression of reflex cutaneous vasodilation (VD) is dependent on nitric oxide (NO) and is attenuated with essential hypertension. Decreased NO-dependent VD may be due to 1) increased oxidant stress and/or 2) decreased L-arginine availability through upregulated arginase activity, potentially leading to increased superoxide production through uncoupled NO synthase (NOS). The purpose of this study was to determine the effect of antioxidant supplementation (alone and combined with arginase inhibition) on attenuated NO-dependent reflex cutaneous VD in hypertensive subjects. Nine unmedicated hypertensive [HT; mean arterial pressure (MAP) = 112 [+ or -] 1 mmHg] and nine age-matched normotensive (NT; MAP = 81 [+ or -] 10 mmHg) men and women were instrumented with four intradermal microdialysis (MD) fibers: control (Ringer), NOS inhibited (NOS-I; 10 mM [N.sup.G]-nitro-L-arginine), L-ascorbate supplemented (Asc; 10 mM L-ascorbate), and Asc + arginase inhibited [Asc+A-I; 10 mM L-ascorbate + 5 mM (S)-(2-horonoethyl)-L-cysteine-HC1 + 5 mM [N.sup.[omega]]-hydroxy-nor-L-arginine]. Oral temperature was increased by 0.8[degrees]C via a water-perfused suit. [N.sup.G]-nitro-L-arginine was then ultimately perfused through all MD sites to quantify the change in VD due to NO. Red blood cell flux was measured by laser-Doppler flowmetry over each skin MD site, and cutaneous vascular conductance (CVC) was calculated (CVC = flux/MAP) and normalized to maximal CVC (%CV[C.sub.max]; 28 mM sodium nitroprusside + local heating to 43[degrees]C). During the plateau in skin blood flow ([DELTA][T.sub.or] = 0.8[degrees]C), cutaneous VD was attenuated in HT skin (NT: 42 [+ or -] 4, HT: 35 [+ or -] 3 %CV[C.sub.max]; P < 0.05). Asc and Asc+A-I augmented cutaneous VD in HT (Asc: 57 [+ or -] 5, Asc+A-I: 53 [+ or -] 6 %CV[C.sub.max]; P < 0.05 vs. control) but not in NT. %CV[C.sub.max] after NOS-I in the Asc- and Asc+A-I-treated sites was increased in HT (Asc: 41 [+ or -] 4, Asc+A-I: 40 [+ or -] 4, control: 29 [+ or -] 4; P < 0.05). Compared with the control site, the change in %CV[C.sub.max] within each site after NOS-I was greater in HT (Asc: -19 [+ or -] 4, Asc+A-I: -17 [+ or-] 4, control: -9 [+ or -] 2; P < 0.05) than in NT. Antioxidant supplementation alone or combined with arginase inhibition augments attenuated reflex cutaneous VD in hypertensive skin through NO- and non-NOdependent mechanisms. skin blood flow; essential hypertension; oxidative stress; temperature regulation; vitamin C

In order to investigate the three-dimensional (3-D) mechanical properties of blood vessels, a new experimental device is described allowing in vitro static and dynamic measurements on segments of arteries with high technical performances. Static tests are applied to sheep common carotid arteries. Considering a thick-walled cylindrical model of orthotropic material under large deformations, a classical 3-D approach based on strain energy density is used to calculate the resulting mechanical behavior law in radial and circumferencial directions and stresses distribution throughout the wall thickness. Results are presented with reference to unloaded and zero-stress initial state thanks to simple measurements of inner and outer circumferences. A particular ratio relating the two main stresses (circumferential and longitudinal) is calculated that put into the forth the progressive modifications in the direction of the predominant stress in the wall and the specific radial location where these changes occur. We observe that this point location is a function of the test conditions of the specimen, i.e., stretching length and level of pressure. Index Terms--Anisotropy, biorheology, blood vessels, in vitro instrumentation, large strains.