A novel-1364A/C aquaporin 5 gene promoter polymorphism influences the responses to salt loading of the renin-angiotensin-aldosterone system and of blood pressure in young healthy men

BACKGROUND

The family of aquaporin water channels contributes to water and salt homeostasis. AQP5 is a ubiquitously expressed exocrine-type water channel. Functional single nucleotide polymorphisms in AQP5 which alter gene transcription have not yet been described. We, therefore, sequenced the human AQP5 promoter to detect novel sequence variants which could impact upon AQP5 expression and contribute to the phenotypic variability of the renin-angiotensin-aldosterone system (RAAS).

METHOD AND RESULTS

Sequencing of the whole AQP5 promoter revealed a novel-1364A/C polymorphism. Substitution of C for A was associated with increased transcription factor binding as tested by electrophoretic mobility shift assay, but significantly reduced transcriptional activation of the AQP5 gene by cAMP and serum. The C allele was associated with significantly decreased mRNA in human heart and with decreased protein expression in erythrocyte membranes. Finally, we associated AQP5 genotypes with the variability of the RAAS in two independent study cohorts. First, we studied the phenotypic variability of the RAAS in 103 young (26 +/- 3 years) healthy males under an increased dietary salt intake. Increasing salt intake decreased plasma angiotensin II by 25% in AC/CC genotypes but only by 2% in AA genotypes (P = 0.012), and it decreased serum aldosterone by 34% in subjects with AC/CC genotypes but only by 19% in the AA genotypes (P = 0.005). Both genotypes had increased blood pressure under salt diet (P < 0.01), which was significantly more pronounced in AA genotypes (P = 0.029). Second, we investigated associations with variables of the RAAS in 96 old patients (68 +/- 10 years) with coronary artery disease scheduled for coronary artery bypass grafting. Aldosterone serum concentrations were 2-fold (P < 0.001) and angiotensin II plasma concentrations were 4-fold higher in AA genotypes than in AC/CC genotypes while ADH plasma concentrations did not differ.

CONCLUSION

A novel single nucleotide polymorphism in the AQP5 gene promoter alters AQP5 expression in different in vitro systems and cells, and is associated with alterations of variables of the RAAS both in young healthy males and in patients with coronary artery disease.

Collecting duct-derived endothelin regulates arterial pressure and Na excretion via nitric oxide

Mice with a collecting duct-specific deletion of endothelin-1 are hypertensive and have impaired Na excretion. Because endothelin-1 activates NO synthase (NOS) in the collecting duct, we hypothesized that impaired renal NO production in knockout mice exacerbates the hypertensive state. Control and knockout mice were treated chronically with N(G)-nitro-l-arginine methyl ester, and blood pressure (BP) and urinary nitrate/nitrite excretion were assessed. On a normal Na diet, knockout systolic BP was 18 mm Hg greater than in controls. N(G)-nitro-l-arginine methyl ester increased BP in control mice by 30 mm Hg and 10 mm Hg in collecting duct-specific deletion of endothelin-1 knockout mice, thereby abolishing the difference in systolic BP between the groups. A high-Na diet increased BP similarly in both groups. Urinary nitrate/nitrite excretion was lower in knockout mice than in controls on normal or high Na intake. In separate experiments, renal perfusion pressure was adjusted in anesthetized mice, and urinary nitrate/nitrite and Na excretion were determined. Similar elevations of BP increased urinary Na and nitrate/nitrite excretion in control mice but to a significantly lesser extent in knockout mice. Isoform-specific NOS activity and expression were determined in renal inner medulla homogenates from control and knockout mice. NOS1 and NOS3 activities were lower in knockout than in control mice given normal or high-Na diets. However, NOS1 or NOS3 protein expressions were similar in both groups on normal or high-Na intake. These data demonstrate that collecting duct-derived endothelin-1 is important in the following: (1) chronic N(G)-nitro-l-arginine methyl ester-induced hypertension; (2) full expression of pressure-dependent changes in sodium excretion; and (3) control of inner medullary NOS1 and NOS3 activity.

Effect of angiotensin receptor blockade on central haemodynamics in essential hypertension: results of a randomised trial

Objective. Angiotensin-converting enzyme (ACE) inhibitors have been shown to lower central augmentation index (cAI), an index of arterial wave reflection, more than β-blockers. We tested whether this is also true for long-term treatment with an angiotensin receptor blocker (ARB).

Methods. One-hundred and fifty-six subjects with essential hypertension were randomised to treatment with either irbesartan or atenolol. cAI and central blood pressure (BP) were determined by pulse wave analysis from the radial and the carotid artery after six and after 18 months treatment.

Results. Peripheral and central systolic and diastolic BP were reduced to a similar extent A in the two groups. cAI was reduced with irbesartan, but increased with atenolol (derived from the carotid artery: -6±10 vs. -4±12% after six months, p<0.001; —4±12 vs. +1±11% after 18 months; p=0.011). Furthermore, central to peripheral pulse pressure (PP) amplification was unaffected by treatment with irbesartan, but decreased with atenolol.

Conclusions. Although treatment with irbesartan and atenolol similarly decreased peripheral and central BP, only treatment with irbesartan had beneficial effects on arterial wave reflection and preserved PP amplification. These haemodynamic effects may at least partly explain the reported differential effects of ARB versus β-blocker treatment on cardiovascular mortality in patients with essential hypertension.

Effects of nitric oxide synthase inhibition and l-arginine on renal haemodynamics in young patients at high cardiovascular risk

BACKGROUND

Aging and a variety of cardiovascular risk factors are associated with oxidative stress and impaired endothelial function. Whether such an association is already evident in the renal vascular bed in young patients at high cardiovascular risk has not yet been determined.

METHODS

We compared renal haemodynamics in 23 young (age 30+/-5 years) male patients at high cardiovascular risk with impaired lipid metabolism and elevated blood pressure with 23 matched, healthy control subjects (age 28+/-3 years) without cardiovascular risk factors at baseline and following infusions of the nitric oxide (NO) synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA: 4.25mg/kg), the substrate of NO synthase L-arginine (100mg/kg) and the antioxidant Vitamin C (3g, co-infused with L-arginine 100mg/kg).

RESULTS

Baseline renal haemodynamics did not differ between the two groups. Infusion of L-NMMA decreased renal plasma flow (RPF) in both groups to a similar extent (-113+/-95 ml/min versus -128+/-133 ml/min, p=NS). The response of RPF to infusion of L-arginine was more pronounced in high risk patients than in control subjects (+123+/-64.4 ml/min versus +75.6+/-60.2 ml/min, p=0.012) and further exaggerated during co-infusion of L-arginine and Vitamin C (+299+/-164 ml/min versus +175+/-148 ml/min, p=0.003).

CONCLUSIONS

Basal NO activity of the renal vasculature appears to be unaltered in young patients at high cardiovascular risk. However, the greater response of RPF to L-arginine and to Vitamin C co-infused with L-arginine in these young patients suggests that decreased substrate availability for NO synthase and oxidative stress are key factors for alterations in endothelium-dependent vasodilation of the renal vasculature in this young high risk group of patients.

Contrasting actions of endothelin ET(A) and ET(B) receptors in cardiovascular disease

First identified as a powerful vasoconstrictor, endothelin has an extremely diverse set of actions that influence homeostatic mechanisms throughout the body. Two receptor subtypes, ET(A) and ET(B), which usually have opposing actions, mediate the actions of endothelin. ET(A) receptors function to promote vasoconstriction, growth, and inflammation, whereas ET(B) receptors produce vasodilation, increases in sodium excretion, and inhibit growth and inflammation. Potent and selective receptor antagonists have been developed and have shown promising results in the treatment of cardiovascular diseases such as pulmonary arterial hypertension, acute and chronic heart failure, hypertension, renal failure, and atherosclerosis. However, results are often contradictory and complicated because of the tissue-specific vasoconstrictor actions of ET(B) receptors and the fact that endothelin is an autocrine and paracrine factor whose activity is difficult to measure in vivo. Considerable questions remain regarding whether ET(A)-selective or nonselective ET(A)/ET(B) receptor antagonists would be useful in a range of clinical settings.

Contrasting actions of endothelin ET(A) and ET(B) receptors in cardiovascular disease

First identified as a powerful vasoconstrictor, endothelin has an extremely diverse set of actions that influence homeostatic mechanisms throughout the body. Two receptor subtypes, ET(A) and ET(B), which usually have opposing actions, mediate the actions of endothelin. ET(A) receptors function to promote vasoconstriction, growth, and inflammation, whereas ET(B) receptors produce vasodilation, increases in sodium excretion, and inhibit growth and inflammation. Potent and selective receptor antagonists have been developed and have shown promising results in the treatment of cardiovascular diseases such as pulmonary arterial hypertension, acute and chronic heart failure, hypertension, renal failure, and atherosclerosis. However, results are often contradictory and complicated because of the tissue-specific vasoconstrictor actions of ET(B) receptors and the fact that endothelin is an autocrine and paracrine factor whose activity is difficult to measure in vivo. Considerable questions remain regarding whether ET(A)-selective or nonselective ET(A)/ET(B) receptor antagonists would be useful in a range of clinical settings.

Attenuated vasoconstrictor responses to endothelin in afferent arterioles during a high-salt diet

Endothelin-1 (ET-1) is increased in rats on a high-salt (HS) diet and participates in salt-dependent hypertension. Afferent arterioles (AA) are important for long-term blood pressure control, and therefore we hypothesized that a HS diet would alter their responsiveness to ET-1. Sprague-Dawley rats were fed either a normal-salt (NS; 0.66% NaCl) or HS (8%) diet for 1 wk. Diameters of AA were determined in response to increasing concentrations of big ET-1, ET-1, sarafotoxin 6c (S6c), or norepinephrine (NE), using the blood-perfused juxtamedullary nephron technique. ET-1 responses were also determined during blockade of endothelin type A (ETA) or type B (ETB) receptors with 10 nM ABT-627 or 30 nM A-192621, respectively. Expression of ETA and ETB receptors was determined in renal microvessels. Responses of AA to big ET-1, ET-1, and S6c were significantly attenuated during a HS diet (e.g., response to 10−10 M ET-1 in NS vs. HS rats: −52.5 ± 10.2 vs. +5.6 ± 11.3% of control diameter; P < 0.05), with no change in the responses to NE. ETB, but not ETA receptor blockade abolished the different response to ET-1 between the NS and HS groups. ETB receptor expression in renal microvessels was increased in response to HS (17.7 ± 2.4 vs. 6.6 ± 3.0% of β-actin, P = 0.02), whereas ETA receptor expression was unchanged. These results suggest that the reduced vasoconstrictor response of AA to endothelin peptides during a HS diet is mediated by increased vasodilatory function of endothelial ETB receptors. By preserving renal blood flow, this may be an important mechanism to restore sodium balance during a HS diet.

Superoxide scavenging effects of N-acetylcysteine and vitamin C in subjects with essential hypertension

BACKGROUND

It is not known whether the beneficial effects of N-acetylcysteine (NAC) in conditions associated with increased oxidative stress are caused by direct superoxide scavenging. We therefore compared the acute superoxide scavenging efficacy of NAC against vitamin C (VITC) on impaired endothelium-dependent vasodilation in subjects with essential hypertension.

METHODS

In a cross-over randomized study, the effects of intra-arterial administration of either NAC (48 mg/min) or VITC (18 mg/min) were examined in 15 subjects with essential hypertension and in 15 normotensive control subjects. Both endothelium-dependent and endothelium-independent vasodilation were determined as forearm blood flow (FBF) response to the intra-arterial administration of acetylcholine (Ach) and sodium nitroprusside (NP) in doses of 12 and 48 mug/min and 3.2 and 12.8 mug/min, respectively.

RESULTS

Subjects with essential hypertension had impaired responses to both doses of Ach (Delta% FBF to higher dose of Ach: 325 +/- 146 in subjects with essential hypertension v 540 +/- 199 in control subjects; P = .02) and an impaired response to the higher dose of NP (330 +/- 108 v 500 +/- 199; P = .03). The intra-arterial administration of NAC had no effect on these responses (higher dose of Ach: 325 +/- 146 without v 338 +/- 112 with NAC, NS). In contrast, intra-arterial VITC improved both the response to Ach (320 +/- 132 without v 400 +/- 185 with VITC, P = .05) and to NP (383 +/- 162 v 447 +/- 170, P = .05).

CONCLUSIONS

We found that NAC showed no statistically significant effect on either endothelium-dependent or endothelium-independent vasodilation in hypertensive subjects, whereas VITC did. We conclude that NAC is therefore not an effective superoxide scavenger in vivo. Other, nonimmediate effects such as the generation of glutathione may explain the beneficial effects of NAC in conditions associated with oxidative stress.

Lipid-independent effects of statins on endothelial function and bioavailability of nitric oxide in hypercholesterolemic patients

BACKGROUND

Experimental evidence suggests a lipid-independent effect of statins on endothelial function and nitric oxide (NO) availability in humans. We investigated whether improvement in NO availability in hypercholesterolemia can be achieved rapidly with statins before lipid-lowering therapy is complete.

METHODS

We studied 41 patients (52 +/- 11 years) with low-density lipoprotein (LDL) cholesterol > or = 130 mg/dL (179 +/- 45 mg/dL) randomly assigned to treatment either with atorvastatin (20 mg/day) or cerivastatin (0.4 mg/day). Endothelium-dependent vasodilation of the forearm vasculature was measured by plethysmography and intra-arterial infusion of acetylcholine (ACh) after 3 days (n = 18) and 14 days (n = 39) of treatment. NO availability and oxidative stress were assessed by coinfusion of l-NMMA and vitamin C.

RESULTS

After 3 days of treatment, LDL-cholesterol decreased by 11.9% with a further decrease to 29.6% after 14 days ( P < .001). Endothelium-dependent vasodilation improved by +46.7% after 3 days of statin therapy compared with before therapy (ACh 48 microg/min: +15.7 +/- 10.6 vs +10.7 +/- 10.8 mL/min per 100 mL, P < .05). No further improvement in endothelium-dependent vasodilation (+42.7% compared with before therapy) could be demonstrated after 14 days of treatment (ACh 48 microg/min: +17.7 +/- 10.3 vs +12.4 +/- 9.3 mL/min per 100 mL before therapy, P < .001). Coinfusion of ACh plus vitamin C was able to improve endothelium-dependent vasodilation before but not after 3 or 14 days of statin therapy either. The improvement in endothelium-dependent vasodilation after therapy was no longer observed when the NO-synthase inhibitor l-NMMA was coinfused together with ACh.

CONCLUSIONS

Short-term lipid-lowering therapy with statins is able to improve endothelial function and NO availability almost completely after 3 days in hypercholesterolemic patients probably by decreasing oxidative stress. This improvement seems to be more rapid than the accompanying decline in LDL-cholesterol and not related to these lipid changes. This finding can support the concept of lipid-independent effects of statins in humans.

The effect of statins on angiotensin II-induced hemodynamic changes in young, mildly hypercholesterolemic men

BACKGROUND

Angiotensin II type 1 (AT(1)) receptors are well known to mediate angiotensin II (Ang II)-induced pro-atherosclerotic effects. It has been found that hypercholesterolemia influences the expression of AT(1) receptors on vascular smooth muscle cells and that increased density of AT(1) receptors exaggerates the hemodynamic response to Ang II. We analyzed to what extent statins and AT(1) receptor antagonists diminish the vasoconstrictive response to Ang II infusion in hypercholesterolemic patients.

METHODS

A total of 24 male patients with LDL cholesterol levels >130 mg/dL were enrolled in a randomized, cross-over study. After baseline evaluation, 12 patients received first cerivastatin (0.3 mg/day) and the other 12 patients initially received candesartan (8 mg/day) for 3 weeks, with subsequent cross-over of the medication for the second 3-week drug period. The vascular response was analyzed by the increase in mean arterial pressure (MAP) and total peripheral resistance (TPR) during infusion of increasing doses of Ang II at baseline and the end of each treatment period. Hemodynamic changes were also compared with those in 24 normocholesterolemic subjects without any therapy.

RESULTS

At baseline, Ang II provoked a similar increase of MAP and TPR in patients and control subjects. Treatment with cerivastatin did not affect the response to Ang II compared with baseline. By contrast, treatment with candesartan attenuated significantly the response to Ang II compared with baseline and cerivastatin.

CONCLUSIONS

Our hemodynamic data indicate the hypothesis that statins do not reduce the responsiveness to Ang II in resistance arteries of young, mildly hypercholesterolemic patients.

Increased response of renal perfusion to the antioxidant vitamin C in type 2 diabetes

BACKGROUND

Reactive oxygen species play a major role in the development of endothelial dysfunction. It is as yet unspecified whether increased oxidative stress contributes to endothelial dysfunction of the renal vasculature in patients with type 2 diabetes.

METHODS

Renal haemodynamics were studied in 20 patients with type 2 diabetes and arterial hypertension (age 62 +/- 5 years) and 20 non-diabetic hypertensive patients at baseline and following infusions of the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA; 4.25 mg/kg); the substrate of nitric oxide synthase, L-arginine (100 mg/kg); and the antioxidant, vitamin C (3 g, co-infused with L-arginine 100 mg/kg).

RESULTS

The response of renal plasma flow (RPF) to L-NMMA (-54 +/- 62 and -45 +/- 42 ml/min/1.73 m(2); P = NS) and L-arginine (+46 +/- 36 and +49 +/- 25 ml/min/1.73 m(2); P = NS) was not different between diabetic and non-diabetic patients. In contrast, vitamin C induced a more pronounced increase in RPF in diabetic than in non-diabetic patients when co-infused with L-arginine (+71+/-47 and +43+/-33 ml/min/1.73 m(2); P<0.05).

CONCLUSIONS

The difference in the response of renal perfusion to an antioxidant suggests increased formation of reactive oxygen species and thereby reduced nitric oxide bioavailability in the renal vasculature of patients with type 2 diabetes.

Effect of Irbesartan Versus Atenolol on Left Ventricular Mass and Voltage

Regression of hypertensive left ventricular hypertrophy (LVH) is associated with improved prognosis. The aim of this trial was to compare the effects of irbesartan versus atenolol on LVH in subjects with essential hypertension. Because electrocardiographic and echocardiographic parameters of LVH carry disparate prognostic information, both methods were applied in this trial. In the randomized, double-blind, multicenter trial CardioVascular Irbesartan Project, 240 patients with essential hypertension were treated with irbesartan or atenolol for 18 months. Voltage criteria used for LVH were Sokolow index, Cornell index, Cornell voltage×QRS duration product and Lewis index. In parallel, left ventricular mass (LVM) was determined by 2-dimensional guided M-mode echocardiography. After 6 and 18 months, reductions of LVM and voltage criteria for LVH were only found in subjects treated with irbesartan. However, a reduction of LVM was only detectable in subjects within the highest quartile of baseline LVM but not overall. In contrast, reductions of voltage criteria for LVH were detectable after 6 and 18 months even within commonly used normal limits. In conclusion, treatment of hypertension with irbesartan resulted in a significant reduction in the voltage criteria for LVH, although an effect on LVM was only seen in subjects with high baseline LVM. In contrast, atenolol did not lead to reductions in electrocardiographic or echocardiographic parameters of LVH. Because voltage criteria for LVH have been shown to predict cardiovascular outcome independently from LVM, we suggest that both methods should be used to accurately assess the benefits of antihypertensive treatment.

The role of nitric oxide in the regulation of glomerular haemodynamics in humans

BACKGROUND

According to experimental data, the afferent glomerular arteriole is particularly under control of nitric oxide (NO). By use of pharmacological manoeuvres, we examined whether this finding holds true in the human renal circulation in vivo.

METHODS

Seventy-seven volunteers (aged 50+/-9 years) with mild to moderate essential hypertension (n = 57) or arterial normotension (n = 20) were examined. Basal NO activity in the renal circulation was assessed by the change of renal plasma flow (RPF) through systemic infusion of the NO synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA; 4.25 mg/kg). Hypertensive patients were treated over 8 weeks with either the calcium-channel blocker amlodipine or the AT(1)-receptor blocker valsartan, primarily dilating the afferent and efferent arteriole, respectively. Subsequently, renal haemodynamics and NO activity in the renal circulation were determined again.

RESULTS

L-NMMA reduced RPF in normotensive (by 57+/-70 ml/min/1.73 m(2); P<0.01) and hypertensive subjects (by 46+/-56 ml/min/1.73 m(2); P<0.001) with no significant difference between the two groups. The decrease of RPF through L-NMMA was closely related with the glomerular filtration rate (GFR; r = 0.39, P<0.001). Administration of amlodipine increased GFR by 7.1+/-12.1 ml/min/1.73 m(2); (P<0.01) and in parallel reduced the response of RPF to L-NMMA to 19+/-48 ml/min/1.73 m(2); (P<0.05). In contrast, valsartan maintained GFR and left the response of RPF to L-NMMA unchanged.

CONCLUSIONS

NO plays an important role in the regulation of human glomerular haemodynamics, probably with a greater contribution to afferent than to efferent arteriolar tone in man.

Direct comparison of the effects of valsartan and amlodipine on renal hemodynamics in human essential hypertension

BACKGROUND

To elucidate the renoprotective mechanism of AT(1)-receptor blockers, we compared the effects of the AT(1)-receptor blocker valsartan with those of the calcium channel blocker amlodipine on renal hemodynamics and microcirculation.

METHODS

A total of 58 patients (50.2 +/- 9.0 years) with mild to moderate essential hypertension were included in a randomized, double-blind study to receive either valsartan (80 to 160 mg) or amlodipine (5 to 10 mg). Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured before and after 8 weeks of treatment. Glomerular hydrostatic pressure (P(Glo)) and resistances of the afferent (R(A)) and efferent (R(E)) arterioles were calculated according to the Gomez formulas.

RESULTS

Blood pressure control was similar in both groups. RPF did not change with either treatment. In contrast, GFR increased with amlodipine (+8 +/- 14 mL/min; P <.01) but was preserved with valsartan. Amlodipine caused a more marked increase in the R(E)/R(A) ratio than valsartan (+0.26 +/- 0.26 v +0.13 +/- 0.24, P <.05), which was paralleled by an increase in P(Glo) in patients treated with amlodipine (+1.9 +/- 4.3 mm Hg; P <.05) but not in those treated with valsartan.

CONCLUSIONS

At similar blood pressure control, valsartan maintained GFR and P(Glo), whereas amlodipine led to glomerular hyperfiltration and an increase in P(Glo). The results might explain the favorable renal outcome with AT(1)-receptor blocker therapy.

Rapid nongenomic effects of aldosterone on human forearm vasculature

The impact of aldosterone in cardiovascular disease and hypertension has recently gained new interest. Aldosterone is now suggested to be a more common cause of hypertension than previously believed and has been linked to myocardial fibrosis, independent of its hypertensive effects. Finally, rapid nongenomic aldosterone effects have been proposed to be important in hypertension, in addition to its genomic effects. Forty-eight healthy male volunteers were examined in a randomized, placebo-controlled, double-blind crossover trial to elucidate the rapid nongenomic, vascular effects of aldosterone in humans. Forearm blood flow was measured by venous occlusion plethysmography. First, aldosterone (500 ng/min) and placebo were infused into the brachial artery for 8 minutes. The volunteers then received ascending doses of acetylcholine, NG-monomethyl-L-arginine (L-NMMA), sodium nitroprusside, or phenylephrine. Aldosterone increased forearm blood flow (P<0.001, ANOVA). The maximum effect was an increase in forearm blood flow with aldosterone of 7.9+/-2.6% compared with 0.1+/-1.9% with placebo treatment after 8 minutes. With aldosterone, L-NMMA induced a greater vasoconstriction (P<0.05, ANOVA), sodium nitroprusside induced an attenuated vasoconstriction (P<0.01, ANOVA), and phenylephrine induced an exaggerated vasoconstriction (P<0.01, ANOVA) within minutes as compared with placebo. These data suggest that aldosterone acts through rapid nongenomic effects at the endothelium by increasing NO release and at the vascular smooth muscle cells by promoting vasoconstriction. This is consistent with in vitro data showing an increase in intracellular calcium in both cell types. Disturbances of these aldosterone effects on both levels might be important in promoting hypertension.

Vitamin C augments the renal response to L-arginine in smokers

BACKGROUND

In the coronary and the forearm circulations, endothelium-dependent vasomotion is impaired in smokers, but can be augmented by -arginine or vitamin C. We examined whether smoking similarly affects the renal circulation.

METHODS

In 20 smokers (age 26 +/- 4 years) and in 20 non-smokers (age 28 +/- 3 years) changes of renal plasma flow (RPF), glomerular filtration rate (GFR), blood pressure and heart rate in response to the subsequent intravenous infusions of N(G)-monomethyl--arginine (L-NMMA), -arginine and -arginine plus vitamin C were studied by use of a constant infusion input clearance technique.

RESULTS

Systemic haemodynamic parameters did not differ between smokers and non-smokers during each experimental phase. At baseline, RPF and GFR were similar between the groups. The infusion of L-NMMA led to a similar decrease of RPF, while GFR did not change in either group. During the infusion of -arginine RPF increased similarly. Finally, the co-infusion of -arginine plus vitamin C led to a significantly greater increase of RPF (+277 +/- 395 vs +79 +/- 76 ml/min, P = 0.03) and GFR (+12.1 +/- 10.6 vs +3.4 +/- 11.2 ml/min, P = 0.02) in smokers as compared to non-smokers.

CONCLUSIONS

L-NMMA-induced vasoconstriction of the renal vasculature was similar in smokers compared to non-smokers. -arginine alone induced a similar increase of RPF. The co-infusion of vitamin C and -arginine led to a greater increase of RPF and GFR in smokers. This might suggest that oxidative stress is increased in the renal vasculature of smokers.

The C242T p22phox polymorphism and endothelium-dependent vasodilation in subjects with hypercholesterolaemia

Oxidative stress plays a major pathogenetic role in cardiovascular disease. The C242T variant of the CYBA gene encoding the p22phox subunit of the NAD(P)H oxidase, a major source of superoxide production, has been shown to be associated with coronary artery disease and with vascular superoxide production in human veins ex vivo. Since superoxide degrades nitric oxide (NO), we hypothesized that the C242T variant influences endothelium-dependent vasodilation of the human forearm vasculature in vivo. In the present study, 90 subjects with elevated cholesterol levels were stratified for the C242T polymorphism of the CYBA p22phox gene. Endothelium-dependent and -independent vasodilation were assessed by plethysmographic monitoring of forearm blood flow responses to intra-arterial infusion of acetylcholine and sodium nitroprusside respectively. N(G)-Monomethyl-L-arginine (L-NMMA) was infused to analyse NO-mediated basal vascular tone. Baseline parameters (age, gender, blood pressure, body mass index, cholesterol level) were similar across the genotypes. No differences in forearm blood flow responses to the intra-arterial infusion of acetylcholine, sodium nitroprusside or L-NMMA were found across the CYBA p22phox genotypes. Our sample size of n =90 had a power of >80% (beta=0.20) with a P value of <0.05 (alpha=0.05) to detect a difference greater than 156% in the forearm blood flow response to acetylcholine across genotypes (S.D. 336%; average increase in forearm blood flow=514%). In conclusion, at a power of 80%, our study excludes a major effect of the C242T CYBA p22phox polymorphism on acetylcholine-mediated endothelium-dependent vasodilation and basal NO-mediated vascular tone of the human forearm circulation in subjects with hypercholesterolaemia.

L-arginine-induced vasodilation of the renal vasculature is not altered in hypertensive patients with type 2 diabetes

OBJECTIVE

Diabetes, arterial hypertension, hypercholesterolemia, and aging are associated with endothelial dysfunction in various vasculatures. Endothelium-dependent vasodilation of the renal vasculature cannot be easily assessed, but infusion of L-arginine, the substrate of endothelial nitric oxide synthase, leads to an increase in renal plasma flow (RPF) in humans. We have examined the effect of L-arginine infusion on renal hemodynamics in hypertensive patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty-three elderly patients with type 2 diabetes (age, 65 +/- 6 years; HbA(1c), 7.8 +/- 1.6%) with coexisting arterial hypertension (158 +/- 19/83 +/- 11 mmHg) and elevated cholesterol levels (total cholesterol, 215 +/- 33 mg/dl) were examined. These patients were compared with a young and healthy reference group (n = 20; age, 26 +/- 2 years). The effect of L-arginine infusion (100 mg/kg over 30 min) on RPF and glomerular filtration rate were measured using the constant input clearance technique with p-aminohippurate and inulin, respectively.

RESULTS

L-arginine infusion similarly influenced renal hemodynamics in patients and reference subjects: RPF increased by 7 +/- 11 and 7 +/- 11% in diabetic and reference subjects, respectively (P = NS). Other parameters of renal hemodynamics such as glomerular filtration rate (5 +/- 5 vs. 4 +/- 4%) and filtration fraction (-1 +/- 8 vs. -1 +/- 9%) were not significantly different between diabetic and reference subjects, too.

CONCLUSIONS

L-arginine-induced vasodilation of the renal vasculature is not different between a group of hypertensive diabetic patients and a young, healthy reference group. These data were obtained using low-dose L-arginine infusion.

Effect of AT1 receptor blockade on endothelial function in essential hypertension

BACKGROUND

Angiotensin II adversely affects endothelial function and NO availability. We analyzed the effect of AT(1) receptor blockade on endothelium-dependent vasodilation and basal nitric oxide (NO) production and release in hypertensive patients.

METHODS AND RESULTS

Sixty patients (53 +/- 10 years) with essential hypertension were randomized to 6 weeks of double-blind therapy with either valsartan (80 mg), hydrochlorothiazide (HCTZ) (25 mg), or placebo once daily. Basal NO production and release was assessed by measuring forearm blood flow (FBF) in response to intra-arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA), and endothelium-dependent vasodilation by measuring FBF in response to intra-arterial administration of acetylcholine, respectively. Intra-arterial infusion of noradrenaline and sodium nitroprusside was used to assess endothelium-independent changes in FBF. Blood pressure (BP) similarly decreased with active treatments (P < .001). After valsartan treatment, the decrease of FBF in response to L-NMMA was augmented (4 micromol/min L-NMMA, -1.3 +/- 1.2 after v -0.5 +/- 1.1 mL/min/100 mL before therapy, P < .02; 8 micromol/min L-NMMA: -1.7 +/- 1.3 after v -1.1 +/- 1.2 mL/min 100 mL before therapy, P < .05). No improvement was found after placebo or HCTZ treatment. Changes in L-NMMA-induced decrease of FBF with valsartan treatment were not related to BP changes. Neither drug substantially modified the response of FBF induced by intra-arterial infusion of acetylcholine, noradrenaline, and sodium nitroprusside.

CONCLUSIONS

The AT(1) receptor blockade with valsartan improved basal NO production and release. The effect seems to be BP independent, as BP reduction with HCTZ failed to increase NO availability.