Relationship between the circulating and vascular renin-angiotensin system and the vasodilating effect of captopril in human hypertension

A vascular renin-angiotensin system (RAS) is present in the forearm vasculature of essential hypertensive patients and is closely related to the circulating renin profile. To test whether the haemodynamic effect of acute intrabrachial administration of captopril is related to the circulating and/or vascular RAS, 31 hypertensive patients were selected and divided into four groups according to their different circulating RAS profile (n = 7 hypertensive patients with primary aldosteronism and suppressed plasma renin activity; n = 7 low renin essential hypertensive patients; n = 8 normal renin essential hypertensive patients; n = 9 high renin renovascular hypertensive patients). The forearm net balance of active renin, plasma renin activity and angiotensin II, obtained by intrabrachial infusion of the beta-adrenergic receptor agonist isoproterenol (0.03, 0.1, 0.3 microg/100 ml/min) and calculated as the product of the venous-arterial plasma concentration gradient and forearm blood flow (FBF), was closely related to the circulating RAS. Captopril (0.25, 2.5, 25 microg/100 ml/min per 20 min each dose) unchanged basal FBF in the primary aldosteronism and low renin groups (FBF increase: from 3.9 +/- 0.4 to a maximum of 4.1 +/- 0.5 and from 3.8 +/- 0.3 to a maximum of 4.3 +/- 0.5 ml/100 ml/min, respectively), whereas it caused slight vasodilation in the normal renin group (from 3.9 +/- 0.3 to a maximum of 5.3 +/- 0.7 ml/100 ml/min), and pronounced vasodilation in the high renin group (from 4.0 +/- 0.4 to a maximum of 6.4 +/- 0.5 ml/100 ml/min). Captopril-induced vasodilation showed a significant direct correlation with the circulating and vascular RAS. The present data, while confirming the existence of a vascular RAS in the forearm of hypertensive patients indicate that the acute vasodilating effect of intrabrachial captopril is linked to a stimulated RAS, either circulating or vascular, supporting the evidence that, in acute conditions, ACE inhibitors exert their vasodilating effect through the RAS blockade.

Hsp90 regulation of endothelial nitric oxide synthase contributes to vascular control in portal hypertension

The molecular chaperone, heat shock protein 90 (Hsp90), acts as an intermediate in the signaling cascades leading to activation of endothelial nitric oxide synthase (eNOS). In this study, we examine the participation of this pathway in nitric oxide (NO)-dependent vasodilation in the rat mesentery in vitro. In normal animals, immunoprecipitation of eNOS from intact mesentery coimmunoprecipitates Hsp90 and, additionally, both eNOS and Hsp90 colocalize to the endothelial lining of mesenteric vessels. In the perfused mesenteric vasculature of normal animals, geldanamycin (GA), a specific inhibitor of Hsp90 signaling, attenuates ACh-dependent vasodilation but does not affect vasodilation in response to sodium nitroprusside. Next, studies were performed in animals with experimental portal hypertension induced by portal vein ligation (PVL). In PVL animals, NOS catalytic activity is markedly enhanced in mesenteric tissue and the perfused mesentery is hyporesponsive to the vasoconstrictor methoxamine (MTX). GA significantly potentiates MTX-induced vasoconstriction after PVL, thereby partially reversing the hyporeactivity to this agent exhibited in the mesenteric vasculature after PVL. These studies suggest that Hsp90 can act as a signaling mediator of NO-dependent responses in the mesenteric circulation and indicate that the excessive NO production observed in portal hypertension is mediated in part through Hsp90 signaling.

Effects of oral folic acid supplementation on endothelial function in familial hypercholesterolemia. A randomized placebo-controlled trial

BACKGROUND

Folates have been suggested to be of benefit in reducing cardiovascular risk. The present study was designed to examine whether oral folic acid supplementation could improve endothelial function as an intermediate end point for cardiovascular risk in patients with increased risk of atherosclerosis due to familial hypercholesterolemia (FH).

METHODS AND RESULTS

In a prospective, randomized, double-blind, placebo-controlled study with crossover design, we evaluated the effects of 4 weeks of treatment with oral folic acid (5 mg PO) on endothelial function in FH. In 20 FH patients, forearm vascular function was assessed at baseline, after 4 weeks of folic acid treatment, and after 4 weeks of placebo treatment by venous occlusion plethysmography, with serotonin and sodium nitroprusside used as endothelium-dependent and -independent vasodilators. In addition, we examined the vasoconstrictor response to the NO synthase inhibitor N(G)-monomethyl-L-arginine to assess basal NO activity. In FH patients, folic acid supplementation restored the impaired endothelium-dependent vasodilation, whereas it did not significantly influence endothelium-independent vasodilation or basal forearm vasomotion. There was a trend toward improvement in basal NO activity.

CONCLUSIONS

These data demonstrate that oral supplementation of folic acid can improve endothelial function in patients with increased risk of atherosclerotic disease due to hypercholesterolemia, without changes in plasma lipids.

Characterisation of vortex shedding in vascular anastomosis models using pulsed Doppler ultrasound

Vortex shedding at vascular anastomoses were investigated in vitro using a 20 MHz pulsed-wave Doppler velocimeter. Centreline velocity measurements were made at various axial distances in simplified polyurethane models of proximal and distal end-to-side anastomoses of angles 15, 30, 45, 60 and 80 degrees using pulsatile flow waveforms similar to those in femoropopliteal bypass grafts. The in-phase and quadrature Doppler signals were recorded and the maximum frequency waveform, averaged over 64 cycles, was obtained using short-time Fourier transform. A fourth-order Butterworth low-pass filter was employed to separate the vortex velocity signal from the convective velocity. The vortex signal envelope was calculated using a Hilbert transform method and the vortex amplitude was taken as the maximum of this envelope. The results show that higher vortex amplitude were found in the proximal anastomoses and under resting flow conditions. Although the vortex amplitudes generally increased with angles of anastomosis, they were found to be higher in the 60 degrees than in the 80 degrees proximal anastomosis. The vortex structures were investigated using spectrograms and these show prominent features at 40-50 Hz indicative of the short-duration oscillatory signals during the decelerative phase of systole expected from the passage of vortices. The study indicates that flow disturbances due to vortex shedding may be a common feature in femoropopliteal bypass grafts.

Reduction in vascular responsiveness to adrenomedullin during sepsis

BACKGROUND

Although sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase, the mechanism responsible for the transition from the hyperdynamic to the hypodynamic state remains unknown. Since recent studies have shown that adrenomedullin (ADM), a novel potent vasodilatory peptide, is upregulated during sepsis, the aim of this study was to determine whether the reduced vascular responsiveness to ADM is associated with the transition from the hyperdynamic phase to the hypodynamic phase of sepsis.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 and 10 h (i.e., the hyperdynamic phase of sepsis) or 20 h (the hypodynamic phase) after CLP, the thoracic aorta or small intestine was harvested and preconstricted with norepinephrine. Adrenomedullin (10(-7) M) was applied and the percentage of ADM-induced vascular relaxation in the aortic ring and isolated small intestine was determined.

RESULTS

The responsiveness to ADM in the thoracic aorta was not altered at 5-10 h, but decreased significantly at 20 h after CLP. Although ADM-induced relaxation in resistance blood vessels of the small intestine did not change at 5 h, it decreased markedly at 10 and 20 h after the onset of sepsis.

CONCLUSIONS

Since the transition from hyperdynamic to hypodynamic sepsis takes place between 10 and 20 h after CLP, it is likely that reduced vascular responsiveness to ADM may be responsible for such an event during the course of polymicrobial sepsis. In view of this, maintenance of vascular ADM responsiveness by pharmacologic agents appears to be a novel approach for preventing or delaying the occurrence of hypodynamic sepsis and septic shock.

Control of cutaneous blood vessels in psoriatic plaques

The aim of this study was to compare local blood flow in psoriatic plaques before and after provocations known to alter cutaneous vascular resistance, in order to determine whether plaque hyperemia is caused by a failure of normal vascular control mechanisms. Cutaneous blood flow was recorded using a laser Doppler flowmeter over plaque skin (plaque site) and clinically normal skin (nonplaque site) on the opposite arm, at least 5 cm away from the nearest plaque. It is important to note that most of the laser Doppler signal comes from the subpapillary plexus of the skin and only a small portion (2%-10%) is produced by capillary blood flow. In the psoriatic plaques the basal flux was between nine and 13 times greater than nonplaque skin. The biologic zero (a signal independent of perfusion, which also persists after complete proximal arterial occlusion) was also significantly greater at plaque sites compared with nonplaque sites. Sympathetic and local vasoconstriction in psoriatic skin was shown to be intact and responses to vasodilator tests were likewise intact, i.e., there was no failure of response to normal vascular control mechanisms, albeit some quantitative differences. Tests of vasodilatation indicated that, although basal flux is high in plaque compared with nonplaque skin, arterioles supplying plaque skin can dilate further, i.e., lesional arterioles are not normally maximally dilated but have a basal constrictor tone. Interestingly, the red cell flux at maximum dilatation in nonplaque skin is less than even the basal flux in plaque skin. This means that in plaque skin either there are more arterioles than in nonplaque skin, or there is chronic, structural widening of the existing arterioles in plaque skin.

Effect of ketorolac in pediatric sickle cell vaso-occlusive pain crisis

BACKGROUND

Ketorolac is a parenteral, nonsteroidal analgesic that does not have a narcotic's risks of respiratory depression, hypotension, or dependence. Its usefulness in providing pain relief in pediatric patients with acute vaso-occlusive crisis of sickle cell disease has not been studied to date.

METHODS

Twenty-nine patients with sickle cell disease between the ages of 5 and 18 years who presented to The Children's Hospital of Alabama emergency department (ED) with 41 distinct episodes of acute vaso-occlusive pain crisis were enrolled prospectively and randomized to receive either 0.9 mg/kg intravenous (IV) ketorolac or placebo in a double-blind fashion. All patients also received IV fluids and an initial 0.1 mg/kg of IV morphine. Subsequent standardized doses of morphine were given every 2 hours over a 6-hour observation period based upon severity of pain as scored by a 10-cm linear visual analog scale (VAS). Vital signs and pain severity were recorded initially and assessed hourly. Disposition was made at the end of the observation period.

RESULTS

Patients receiving ketorolac and those receiving placebo were of similar age, weight, gender, number of prior ED visits, number of prior hospital admissions, duration of pain prior to presentation, and initial pain score. The total dose of morphine received, reduction in severity of pain as measured by VAS, rate of hospital admission, and rate of return to the ED for discharged patients did not differ significantly between the two groups.

CONCLUSION

We were unable to demonstrate a synergistic analgesic effect for ketorolac in the treatment of pain from acute vaso-occlusive crisis in pediatric sickle cell disease. Further investigations involving larger samples of sickle cell patients may be needed to further define a role for ketorolac in the acute management of sickle cell vaso-occlusive pain.

The natural course of atherosclerosis. Part II: vascular remodeling. Bruneck Study Group

Arterial remodelling is a potentially important component in atherogenesis aimed at delaying the development of significant lumen compromise. Current knowledge on this phenomenon is mainly restricted to experimental evaluations and a few postmortem studies. We used high-resolution duplex ultrasound to study 5-year changes (1990 to 1995) in vessel geometry in a large random sample of the general population (Bruneck Study). Carotid arteries free of atherosclerosis and wall thickening preserved a normal size to high ages. In contrast, common and internal carotid arteries with elevated intima-media thickness (>/=50th percentile) experienced marked age-dependent dilation that started already in the 5th decade and continuously accelerated thereafter (structural ageing). Vessel diameters were subject to complex regulation involving morphometric characteristics, sex, wall thickness, hypertension, LDL cholesterol levels, and alcohol consumption. Vascular remodelling secondary to incident or slowly progressive (mural) atherosclerosis included local compensation and a generalised dilation response of vascular segments not primarily affected. Adaptive enlargement at the site of active atherogenesis effectively preserved a near-normal lumen in most instances. The current study identified a second main type of plaque growth, characterized by episodic marked increase in lesion volume probably on the basis of plaque thrombosis. In this setting, we did not observe maximum but insufficient compensation but instead usually observed no compensation at all. Failure of vascular remodelling and marked expansion in plaque size acted synergistically in producing significant lumen compromise. The current prospective survey describes fundamental principles and various facets of arterial remodelling and vascular biology in the general population (in vivo). Vessel geometry was subject to marked temporal changes and showed a correspondingly complex (multifactorial) and dynamic regulation. Vascular remodelling emerged as an important compensatory process in human atherogenesis, which crucially contributed to the determination of lumen obstruction. Efficacy and failure of compensation primarily depended on the type and pathomechanisms of underlying atherogenesis and only in second instance on plaque size and location.

Embryonic lethality and vascular defects in mice lacking the Notch ligand Jagged1

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism essential for embryonic development in mammals. Mutations in the human JAGGED1 ( JAG1 ) gene, which encodes a ligand for the Notch family of transmembrane receptors, cause the autosomal dominant disorder Alagille syndrome. We have examined the in vivo role of the mouse Jag1 gene by creating a null allele through gene targeting. Mice homozygous for the Jag1 mutation die from hemorrhage early during embryogenesis, exhibiting defects in remodeling of the embryonic and yolk sac vasculature. We mapped the Jag1 gene to mouse chromosome 2, in the vicinity of the Coloboma ( Cm ) deletion. Molecular and complementation analyses revealed that the Jag1 gene is functionally deleted in the Cm mutant allele. Mice heterozygous for the Jag1 null allele exhibit an eye dysmorphology similar to that of Cm /+ heterozygotes, but do not exhibit other phenotypes characteristic of Cm /+ mice or of humans with Alagille syndrome. These results establish the phenotype of Cm /+ mice as a contiguous gene deletion syndrome and demonstrate that Jag1 is essential for remodeling of the embryonic vasculature.

Evaluation of flow characteristics of soft-tissue vascular malformations using technetium-99m labelled red blood cells

The estimation of intralesional haemodynamics is crucial in determining appropriate treatment for soft-tissue vascular malformations. The aim of this study was to develop a method to evaluate the flow characteristics of soft-tissue vascular malformations using technetium-99m labelled red blood cells (99mTc-RBCs). Seventy-nine soft-tissue vascular malformations, including 20 arteriovenous malformations and 59 venous malformations, in 57 patients were examined. Following the intravenous injection of 99mTc-RBCs, dynamic imaging was performed for 30 min with the lesion in the field of view (99mTc-RBC flow study). A time-activity curve was generated for the lesion, and the lesion was categorized as a high-flow or low-flow lesion by visual inspection of the curve. In low-flow lesions, mean vascular transit time (MTT) was calculated by curve fitting based on a two-compartment model. Twenty-nine lesions in 19 patients were examined twice, and reproducibility was assessed. In 23 venous malformations in 16 patients, 99mTc-Sn colloid was percutaneously injected into the intravascular space of the lesion, and dynamic data of 5-min duration were acquired (direct puncture scintigraphy). MTT was estimated from the washout curve and compared with MTT estimated by 99mTc-RBC flow study. 99mTc-RBC flow study classified all 20 arteriovenous malformations as high-flow lesions and all 59 venous malformations as low-flow lesions. In the low-flow lesions, MTT estimated by 99mTc-RBC flow study ranged from 61.2 to 2174.9 s. In the reproducibility study, complete concordance in classification and high correlation in MTT were shown between the first and second examinations. MTT estimated by 99mTc-RBC flow study was significantly correlated with that estimated by direct puncture scintigraphy. In summary, 99mTc-RBC flow study provides a quantitative indicator of intralesional haemodynamics in low-flow lesions in addition to accurate distinction between high-flow and low-flow lesions. The results of this study suggest the feasibility of detailed evaluation of flow characteristics in soft-tissue vascular malformations using 99mTc-RBCs.

Increased renal resistive index in patients with essential hypertension: a marker of target organ damage

BACKGROUND

Increased renal resistance detected by ultrasound (US) Doppler has been reported in severe essential hypertension (EH) and recently was shown to correlate with the degree of renal impairment in hypertensive patients with chronic renal failure. However, the pathophysiological significance of this finding is still controversial.

METHODS

In a group of 211 untreated patients with EH, we evaluated renal resistive index (RI) by US Doppler of interlobar arteries and early signs of target organ damage (TOD). Albuminuria was measured as the albumin to creatinine ratio (ACR) in three non-consecutive first morning urine samples. Left ventricular mass was evaluated by M-B mode echocardiography, and carotid wall thickness (IMT) by high resolution US scan.

RESULTS

RI was positively correlated with age (r=0.25, P=0.003) and systolic blood pressure (SBP) (r=0.2, P=0.02) and with signs of early TOD, namely ACR (r=0.22, P=0.01) and IMT (r=0.17, P<0.05), and inversely correlated with renal volume (r=-0.22, P=0.01) and diastolic blood pressure (r=-0.23, P=0.006). Multiple linear regression analysis demonstrated that age, gender, ACR and SBP independently influence RI and together account for approximately 20% of its variations (F=8.153, P<0.0001). When clinical data were analysed according to the degree of RI, the patients in the top quartile were found to be older (P<0.05) and with higher SBP (P<0.05) as well as early signs of TOD, namely increased ACR (P<0.002) and IMT (P<0.005 by ANOVA), despite similar body mass index, uric acid, fasting blood glucose, lipid profile and duration of hypertension. Furthermore, patients with higher RI showed a significantly higher prevalence of microalbuminuria (13 vs 12 vs 3 vs 33% chi2=11.72, P=0.008) and left ventricular hypertrophy (40 vs 43 vs 32 vs 60%, chi2=9.25, P<0.05).

CONCLUSIONS

Increased RI is associated with early signs of TOD in EH and could be a marker of intrarenal atherosclerosis.

Vascular reactivity in preeclampsia

It has long been known that vascular reactivity is altered in preeclamptic patients compared with normal pregnant women. This change even occurs weeks earlier than any clinical manifestation of the disease. Many investigators believe that the conditions for the development of preeclampsia are set as early as the first trimester. These changes in vascular reactivity appear to be independent of the blood pressure because they also occur in chronic hypertensive women destined to have preeclampsia. This review focuses on these changes in vascular reactivity reported in preeclampsia. Increased reactivity of the blood vessels in preeclampsia has been described in most, but not all, studies. The cause for the differences in reactivity between vessels from preeclamptic and normal pregnant women is not known. However, it cannot be attributed solely and with certainty to abnormalities in endothelium-dependent relaxation or the nitric oxide system because the study results published to date remain contradictory. In addition to functional differences, vessels from normal pregnant and preeclamptic women show distinct mechanical properties.

Effects of cytokines on nitric oxide pathways in human vasculature

Proinflammatory cytokines exert a number of important effects on vascular reactivity. At one end of the spectrum, certain cytokines may induce vascular paresis leading to profound vasodilatation and hyporesponsiveness to constrictor stimuli. This may be relevant to the pathogenesis of septic shock and other types of inflammatory vasodilatation. At the other end of the spectrum, inflammatory cytokines can impair endothelium-dependent dilatation and the endothelium may lose its ability to respond to circulating hormones or autacoids. This effect may case a predisposition to vessel spasm, thrombosis or atherogenesis. Studies in human vessels suggest that interleukin-1 is particularly important as a mediator of inflammatory dilatation; the underlying mechanisms include induction of the inducible isoform of nitric oxide synthase in vascular smooth muscle, or over-production of nitric oxide from the endothelial isoform of nitric oxide synthase. Induction of the enzyme GTP cyclohydrolase 1 and consequent production of tetrahydrobiopterin contributes to the increase in the activity of endothelial nitric oxide synthase. In contrast, tumour necrosis factor-alpha considerably impairs endothelium-dependent relaxation. The mechanisms of these effects are not yet fully understood, but tumour necrosis factor can induce endothelial dysfunction in human endothelial cells in culture, and human blood vessels in vitro and in vivo. The implications of these observations for cardiovascular disease are discussed.

Neurogenic plasma leakage in mouse airways

1. This study sought to determine whether neurogenic inflammation occurs in the airways by examining the effects of capsaicin or substance P on microvascular plasma leakage in the trachea and lungs of male pathogen-free C57BL/6 mice. 2. Single bolus intravenous injections of capsaicin (0.5 and 1 micromol kg(-1), i.v.) or substance P (1, 10 and 37 nmol kg(-10, i.v.) failed to induce significant leakage in the trachea, assessed as extravasation of Evans blue dye, but did induce leakage in the urinary bladder and skin. 3. Pretreatment with captopril (2.5 mg kg(-1), i.v.), a selective inhibitor of angiotensin converting enzyme (ACE), either alone or in combination with phosphoramidon (2.5 mg kg(-1), i.v.), a selective inhibitor of neutral endopeptidase (NEP), increased baseline leakage of Evans blue in the absence of any exogenous inflammatory mediator. The increase was reversed by the bradykinin B2 receptor antagonist Hoe 140 (0.1 mg kg(-1), i.v.). 4. After pretreatment with phosphoramidon and captopril, capsaicin increased the Evans blue leakage above the baseline in the trachea, but not in the lung. This increase was reversed by the tachykinin (NK1) receptor antagonist SR 140333 (0.7 mg kg(-1), i.v.), but not by the NK2 receptor antagonist SR 48968 (1 mg kg(-1), i.v.). 5. Experiments using Monastral blue pigment as a tracer localized the leakage to postcapillary venules in the trachea and intrapulmonary bronchi, although the labelled vessels were less numerous in mice than in comparably treated rats. Blood vessels of the pulmonary circulation were not labelled. 6. We conclude that neurogenic inflammation can occur in airways of pathogen-free mice, but only after the inhibition of enzymes that normally degrade inflammatory peptides. Neurogenic inflammation does not involve the pulmonary microvasculature.

Cardiovascular effects of dietary copper deficiency

Dietary copper deficiency may impair cardiovascular health by contributing to high blood pressure, enhancement of inflammation, anemia, reduced blood clotting and arteriosclerosis. The purpose of this review is to compile information on the numerous changes of the heart, blood and blood vessels that may contribute to these cardiovascular defects. These alterations include weakened structural integrity of the heart and blood vessels, impairment of the use of energy by the heart, reduced ability of the heart to contract, altered ability of blood vessels to control their diameter and to grow, and altered structure and function of circulating blood cells. The fundamental causes of these changes rest largely on reduced effectiveness of enzymes that depend on copper for their activity.

Effects of angiotensin-converting enzyme inhibition on vascular remodeling of resistance vessels in hypertensive patients

Essential hypertension is known to be associated with a decrease in the lumen diameter and an increase in the wall thickness to lumen diameter ratio of the resistance vessels. Recently, it has been clarified that this alteration does not necessarily involve vascular growth, but could be due to a rearrangement of the same amount of material, a phenomenon now termed "eutrophic remodeling." These changes are found both in human essential hypertension and in animal models of genetic hypertension. Antihypertensive treatment with angiotensin-converting enzyme (ACE) inhibitors causes a dose-dependent regression of the media to lumen ratio in rats. Clinical studies have now confirmed these findings, showing that when previously untreated essential hypertensive patients are treated with the ACE inhibitor perindopril (PE), the abnormal structure of resistance vessels regresses toward normal values; in contrast, treatment with a beta-blocker does not affect the abnormal vascular structure. The available evidence thus indicates that ACE inhibitors are able to normalize the abnormal resistance vessel structure in essential hypertension, and suggest that this effect may not only be dependent on their ability to reduce blood pressure. This review summarizes these findings, and discusses the extent to which this is desirable.

Renovascular adaptive changes in chronic hypoxic polycythemia

BACKGROUND

Chronic hypoxia in rats produces polycythemia, and the plasma fraction falls, reducing renal plasma flow (RPF) relative to renal blood flow (RBF). Polycythemia also causes increased blood viscosity, which tends to reduce RBF and renal oxygen delivery. We studied how renal regulation of electrolyte balance and renal tissue oxygenation (which is crucial for erythropoietin regulation) are maintained in rats during hypoxic exposure.

METHODS

Rats of two strains with differing polycythemic responses, with surgically implanted catheters in the urinary bladder, femoral artery, and left renal and right external jugular veins, were exposed to a simulated high altitude (0.5 atm) for 0, 1, 3, 14, and 30 days, after which RPF (para-aminohippurate clearance), glomerular filtration rate (GFR, polyfructosan clearance), hematocrit and blood gases were measured, and RBF, renal vascular resistance and hindrance (resistance/viscosity), renal oxygen delivery, and renal oxygen consumption were calculated.

RESULTS

During chronic hypoxia RBF increased, but RPF decreased because of the polycythemia. GFR remained normal because the filtration fraction (FF) increased. Renal vascular resistance decreased, and renal vascular hindrance decreased more markedly. Renal oxygen delivery and consumption both increased.

CONCLUSIONS

During chronic hypoxia GFR homeostasis apparently took precedence over RBF autoregulation. The large decrease in renal vascular hindrance suggested that renal vascular remodeling contributes to GFR regulation. The reduced hindrance also prevented a vicious cycle of increasing polycythemia and blood viscosity, decreasing RBF, and increasing renal hypoxia and erythropoietin release.

Endothelial dysfunction and vascular disease

The endothelium plays an obligatory role in a number of relaxations of isolated arteries. These endothelium-dependent relaxations are due to the release by the endothelial cells of potent vasodilator substances [endothelium-derived relaxing factors (EDRF)]. The best characterized EDRF is nitric oxide (NO). Nitric oxide is formed by the metabolism of L-arginine by the constitutive NO synthase of endothelial cells. In arterial smooth muscle, the relaxations evoked by EDRF are explained best by the stimulation by NO of soluble guanylate cyclase that leads to the accumulation of cyclic GMP. The endothelial cells also release an unidentified substance that causes hyperpolarization of the cell membrane (endothelium-derived hyperpolarizing factor, EDHF). The release of EDRF from the endothelium can be mediated by both pertussis toxin-sensitive (alpha2-adrenergic activation, serotonin, thrombin, aggregating platelets) and insensitive (adenosine diphosphate, bradykinin) G-proteins. In blood vessels from animals with regenerated endothelium, and/or atherosclerosis, there is a selective loss of the pertussis-toxin sensitive mechanism of EDRF-release which favors the occurrence of vasospasm, thrombosis and cellular growth.