Effect of captopril and enalapril on endothelial function in hypertensive patients

Differential effects of quinaprilat and enalaprilat on endothelial function of conduit arteries in patients with chronic heart failure

BACKGROUND

Chronic heart failure (CHF) is associated with endothelial dysfunction, including impaired flow-dependent (endothelium-mediated) dilation (FDD). We have previously shown that ACE inhibition improves endothelium-mediated vasodilation in healthy volunteers. The present study was designed to determine whether ACE inhibition improves the impaired FDD in patients with CHF. Because their affinity to tissue ACE may influence the ability of ACE inhibitors to affect endothelial function, we compared the effects of quinaprilat (high affinity to tissue ACE) and enalaprilat (low affinity to tissue ACE) on FDD in patients with CHF.

METHODS AND RESULTS

High-resolution ultrasound and Doppler were used to measure radial artery diameter and blood flow in patients with CHF. The effects of intra-arterial infusion of quinaprilat 1.6 microg/min (n=15) and enalaprilat 5 microg/min (n=15) were determined at rest and during reactive hyperemia (causing endothelium-mediated dilation) before and after N-monomethyl-L-arginine (L-NMMA) to inhibit endothelial synthesis of nitric oxide. Quinaprilat improved FDD by >40% (10.2+/-0.6% versus 6.9+/-0.6%; P<0.01), whereas enalaprilat had no effect. In particular, the part of FDD mediated by nitric oxide (ie, inhibited by L-NMMA) was increased by >100% with quinaprilat (5.6+/-0.5% versus 2.5+/-0.5%; P<0.01). Enalaprilat had no effect on FDD even when it was infused twice in the same dose (5 microg/min) and up to 30 microg/min. The effect of sodium nitroprusside on radial artery diameter and blood flow was similar in patients treated with quinaprilat, enalaprilat, and placebo.

CONCLUSIONS

Quinaprilat improves FDD in patients with CHF as the result of increased availability of nitric oxide, whereas enalaprilat does not. This observation suggests that intrinsic differences exist between quinaprilat and enalaprilat that determine the ability to improve endothelium-mediated vasodilation, ie, their different affinity to tissue ACE.

Clinical implications of endothelial dysfunction

Endothelial dysfunction is increasingly recognized as an early event in the pathogenesis of cardiovascular disease. This observation is consistent with the growing appreciation of the role of endothelium in maintaining cardiovascular health. Endothelial dysfunction and coronary artery disease are both linked to hypertension, hypercholesterolemia, diabetes mellitus, and cigarette smoking. Modification of these conditions improves both endothelial function and coronary artery disease outcomes. Dietary and lifestyle modifications and antioxidant vitamin supplementation have a beneficial effect on endothelial function, as do angiotensin-converting enzyme inhibitors and lipid-lowering agents. Future studies will determine whether interventions that specifically target endothelial dysfunction can reduce rates of clinical disease.

Impaired endothelial regulation of vascular tone in patients with systemic arterial hypertension

The discovery of the endothelium as a major regulator of vascular tone triggered intense research among basic and clinical investigators to unravel the physiologic and pathophysiologic significance of this phenomenon. Importantly, endothelial modulation of the contractile state of vascular smooth muscle has been shown to be impaired in atherosclerosis and in several conditions known to be associated with the premature development of atherosclerosis. Studies in several different animal models of arterial hypertension, and in patients with both essential and secondary hypertension, have demonstrated an association between elevated systemic blood pressure and impaired endothelium-dependent vascular relaxation. More recently, a diminished bioavailability of nitric oxide (NO) has been identified as a mechanism responsible for endothelial dysfunction in hypertensive patients. Different processes may, in turn, explain this decreased vascular activity of NO. The present review focuses on those clinical studies that are aimed at identifying the precise abnormality responsible for reduced NO-dependent vasodilation in patients with essential hypertension. Understanding of the basic mechanisms of this process may prove to be beneficial for the development of more specific therapies and ultimately for the outcome of hypertensive patients.

Divergent effects of different antihypertensive drugs on endothelium-dependent vasodilation in the human forearm

Several studies indicated an abnormal endothelium-dependent vasodilation (EDV) in hypertensive patients, but no study has systematically investigated the effects of different pharmacologic classes of antihypertensive drugs on EDV. This study aimed to evaluate the effects of three different antihypertensive regimens [angiotensin-converting enzyme (ACE) inhibition, calcium channel blockade, and beta-blockade] on EDV when given locally in the forearm at a constant blood pressure. The increase in forearm blood flow (FBF) during local intraarterial infusions of methacholine (MCh; inducing EDV) and sodium nitroprusside (SNP; inducing endothelium-independent vasodilation, EIDV) was measured in young, normotensive subjects by venous occlusion plethysmography, before and during concomitant local intraarterial infusion of any of the antihypertensive drugs. Without changing baseline FBF, enalaprilat (n=6, 2.4 mg/h) potentiated the increase in FBF induced by MCh [from 22.6+/-2.3 (SD) to 25.4+/-2.3 ml/min/100 ml tissue at 4 microg/min; p < 0.05], but the response to SNP was unchanged. Local intraarterial verapamil infusion (n=6), at a dose individually titrated to keep baseline FBF unchanged, did not alter the response to MCh infusion, whereas the response to SNP was potentiated. A higher dose of verapamil (n=6), which increased baseline FBF, increased both EDV and EIDV significantly in parallel (p < 0.05). The local propranolol infusion (n=6, 1.2 mg/h) attenuated the FBF response to MCh significantly (from 28.9+/-5.7 to 21.5+/-3.2 ml/min/100 ml tissue at 4 microg/min; p < 0.05), whereas both baseline FBF and the response to SNP were unchanged. In conclusion, this investigation showed that commonly used antihypertensive drugs affect endothelial vasodilator function in a different ways. ACE inhibition enhanced EDV, whereas a nonselective beta-blocker attenuated EDV. The calcium channel blocker, verapamil, improved both EDV and EIDV, probably by a direct effect on the vascular smooth-muscle cells.

Antihypertensive treatment improves endothelium-dependent hyperpolarization in the mesenteric artery of spontaneously hypertensive rats

BACKGROUND

The vascular endothelium releases endothelium-derived hyperpolarizing factor (EDHF). The mesenteric arteries of 6- to 8-month-old spontaneously hypertensive rats (SHRs) exhibit an impairment of the hyperpolarization induced by acetylcholine via EDHF.

METHODS AND RESULTS

We determined whether antihypertensive treatment can improve EDHF-mediated responses in SHRs. Beginning at age 8 to 9 months, the animals were treated with either enalapril (40 mg x kg(-1) x d(-1)) (SHR-Es) or a combination of hydralazine (25 mg x kg(-1) x d(-1)) and hydrochlorothiazide (7.5 mg x kg(-1) x d(-1)) (SHR-Hs) for 3 months. The control groups were age-matched SHRs (SHR-Cs) and Wistar Kyoto rats (WKYs). The two treatments lowered the blood pressure to comparable extents. The acetylcholine-induced hyperpolarization in the mesenteric artery of treated SHRs improved to a level comparable to that in WKYs (acetylcholine 10(-5) mol/L with norepinephrine 10(-5) mol/L: SHR-E, -14.4 +/- 1.8; SHR-H, -12.0 +/- 1.3; SHR-C, -7.2 +/- 1.2; and WKY, -13.3 +/- 2.3 mV). EDHF-mediated relaxation, as assessed by relaxation to acetylcholine resistant to N(G)-nitro-L-arginine in norepinephrine-contracted rings, was markedly improved in treated SHRs (maximal relaxation: SHR-E, 79.3+/-3.2%; SHR-H, 47.4+/-8.6%; SHR-C, 4.8+/-2.4%; and WKY, 45.1+/-6.0%). When the rings were contracted with 77 mmol/L KCl to eliminate EDHF response, no difference was found in relaxation to acetylcholine among the four groups. Similarly, the hyperpolarization and relaxation to levcromakalim, a K+ channel opener, were comparable among the groups.

CONCLUSIONS

Antihypertensive treatment improved EDHF-mediated hyperpolarization and relaxation in the mesenteric artery in SHRs, whereas NO-mediated relaxation did not appear to be modulated by drug therapy. Thus, alterations in the EDHF system may play a pivotal role in endothelial dysfunction and its improvement with drug therapy in SHRs.

Role of angiotensin-converting enzyme inhibition in reversal of endothelial dysfunction in coronary artery disease

Angiotensin-converting enzyme (ACE) inhibitors have shown unexpected benefits in the prevention of ischemic events in patients with hypertension and congestive heart failure. In addition to these clinical observations, there is a growing body of knowledge about the molecular and cellular effects of ACE inhibitors. For example, ACE inhibition prevents stimulation of smooth muscle cell angiotensin II receptors, thereby blocking both contractile and proliferative actions. Angiotensin II blockade also diminishes the production of superoxide anion, which inactivates ambient nitric oxide. ACE inhibition of kininase II inhibits the breakdown of bradykinin, a direct stimulant of nitric oxide release from the intact endothelial cell. Thus, at the cellular level within the vasculature, ACE inhibition shifts the balance of ongoing mechanisms in favor of those promoting vasodilatory, antiaggregatory, antithrombotic, and antiproliferative effects. These effects underlie the potential benefits of ACE inhibition in the therapy of ischemia and atherosclerosis. Some data is available in humans to show that these effects can be sustained for months, thereby maintaining improved endothelial function and, presumably, allowing the initiation of steps that might alter the progression of atherosclerosis. Definitive information is not yet available in humans to show that ACE inhibition clearly alters the progression of atherosclerosis or diminishes coronary events in uncomplicated coronary disease. This promising area of investigation is, however, the subject of multiple clinical trials, which should provide clarification of this important question in coming years.

Endothelial function and common carotid artery wall thickening in patients with essential hypertension

Intimal-medial thickening of the carotid wall is considered an early marker of atherosclerosis. Endothelial function is impaired in the presence of various cardiovascular risk factors that are implicated in the pathogenesis of atherosclerosis. To evaluate the relationship between vascular reactivity and carotid intimal-medial thickening, in 44 (mean+/-SD age, 45.7+/-8.8 years; range, 28 to 60 years; 31 men and 13 women) patients with essential hypertension who had never been treated and whose history of increased blood pressure was no longer than 12 months, we evaluated several parameters: intimal-medial thickening of the common carotid arteries (by B-mode ultrasound); forearm vascular response (by strain-gauge plethysmography) to intrabrachial infusion of acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg/100 mL forearm tissue per minute), an endothelium-dependent vasodilator, or sodium nitroprusside (1, 2, and 4 microg/100 mL forearm tissue per minute), an endothelium-independent vasodilator; calculated minimal forearm vascular resistances (the ratio between mean arterial pressure and maximal forearm vasodilation induced by 13 minutes of ischemia and 1 minute of exercise); and left ventricular mass index (on echocardiography profile). Carotid wall intimal-medial thickening showed a significant (P<0.001) inverse correlation with vasodilation to acetylcholine (r=-0.58) and age (r=-0.40), whereas no correlation was observed with the response to sodium nitroprusside or with minimal forearm vascular resistances, left ventricular mass index, systolic and diastolic blood pressures, and plasma cholesterol and glucose levels. Moreover, vasodilation to acetylcholine showed no correlation with minimal forearm vascular resistances or left ventricular mass index. Although comparison of different vascular "districts," such as the forearm microcirculation and carotid artery, does not allow for a conclusive interpretation, the present data indicate that in patients with essential hypertension, carotid wall thickening is associated with reduced endothelium-dependent vasodilation and suggest that endothelial dysfunction might be involved in early arterial structural alterations.

Angiotensin-converting enzyme inhibition, but not calcium antagonism, improves a response of the renal vasculature to L-arginine in patients with essential hypertension

Endothelial function has been shown to be impaired in patients with essential hypertension. The purpose of the present study was to determine whether antihypertensive drug therapy improves impaired endothelium-dependent renal vasorelaxation in essential hypertensive patients without atherosclerosis. We evaluated the effects of intravenous infusion of L-arginine (500 mg/kg given over 30 minutes) on systemic and renal hemodynamics in 27 patients with mild to moderate essential hypertension who were randomly assigned to treatment with either the angiotensin-converting enzyme inhibitor imidapril or the calcium antagonist amlodipine for 12 weeks in a double-blind fashion. After the 12 weeks, the decrease in blood pressure was similar in the imidapril (n=14) and amlodipine (n=13) groups. The increase in renal plasma flow was also similar in both groups. L-Arginine-induced renovascular relaxation was increased by imidapril (renal plasma flow, 9.6+/-5.1% to 14.4+/-7.4%; renal vascular resistance, -10.4+/-8.1% to -16.7+/-9.2%, P<0.05, respectively) but not by amlodipine. Urinary excretion of nitrite/nitrate in response to L-arginine was significantly increased by imidapril (90+/-29% to 134+/-63%, P<0.05) but remained unchanged by amlodipine. These findings suggest that angiotensin-converting enzyme inhibition improves the impaired endothelium-dependent renovascular relaxation in patients with essential hypertension due to the increase in nitric oxide production and that the reduction in blood pressure with a calcium antagonist does not play a major role in the potentiation of L-arginine/nitric oxide-mediated effects.

The impact of angiotensin converting enzyme inhibitors on the arterial wall

There is recent interest in the possibility that angiotensin converting enzyme inhibitors (ACE inhibitors) may reduce the damage inflicted on the arterial wall by common cardiovascular risk factors such as hypertension, hyperlipidaemia and ageing. The efficacy of these drugs in blood pressure reduction is accepted, but whether there is an excess benefit on arterial structure and function, conferred by use of ACE inhibitors over more traditional antihypertensives, is still under debate. There is also evidence in animal models to suggest that ACE inhibition is effective in reduction of arterial damage due to experimental hyperlipidaemia. ACE inhibitors not only reduce the conversion of angiotensin I and angiotensin II, which can interact with the sympathetic nervous system, but also prevent the degradation of bradykinin. This means that ACE inhibitors have several potential mechanisms through which they could suppress intimal hypertrophy and prevent endothelial dysfunction, which is believed to precede arteriosclerosis in man. Although much further work is needed to clarify the mechanism underlying the beneficial effects on the arterial wall of this group of drugs, they do appear to have significant potential in the effort to reduce cardiovascular mortality and morbidity, especially in high risk groups.

Endothelial dysfunction: implications for therapy of cardiovascular diseases

OBJECTIVE

To review current literature regarding endothelial dysfunction in cardiovascular diseases and examine implications of these findings for the treatment of various cardiovascular disorders.

DATA SOURCE

A MEDLINE search of basic science articles pertinent to understanding the role of the endothelium in the atherosclerotic process and of clinical trials examining the presence and treatment of impaired endothelium-dependent vascular relaxation was conducted.

STUDY SELECTION

Selected basic science articles and reviews were included to explain the foundation for subsequent clinical trials. All clinical trials examining the treatment of impaired endothelium-dependent vascular relaxation were reviewed.

DATA SYNTHESIS

Endothelial dysfunction characterized by impaired endothelium-dependent vascular relaxation is an early physiologic event in atherogenesis. Endothelial dysfunction in peripheral vasculature serves as a marker for impairment in coronary arteries. Techniques for measuring endothelium-dependent vascular relaxation are specific and have a high positive predictive value for coronary artery disease, but low sensitivity. Various pharmacologic agents have been used in an attempt to improve endothelial function, but only lipid-lowering agents and estrogen supplementation have been shown to improve endothelium-dependent vascular relaxation consistently. Treatments used in patients with heart failure or hypertension fail to demonstrate consistent improvement.

CONCLUSIONS

Endothelial dysfunction serves as a marker for cardiovascular disease, but pharmacologic treatment does not consistently restore normal endothelial function. Nevertheless, some of these agents are known to have positive clinical outcomes. Future research using these techniques will provide greater insight into the effects of many commonly used therapies for cardiovascular disease on the pathobiology of endothelial dysfunction.

Effects of angiotensin converting enzyme inhibition on endothelium-dependent vasodilatation in essential hypertensive patients

BACKGROUND

Essential hypertension is characterized by an impairment of endothelium-dependent vasodilatation.

OBJECTIVE

To test whether antihypertensive treatment with the angiotensin converting enzyme inhibitor lisinopril can improve vasodilatation in response to endothelium-dependent agonists in essential hypertensive patients.

DESIGN AND METHODS

We studied the effect of acute (6-8 h after dosing), prolonged (1 month) and chronic (12 months) lisinopril treatment on forearm blood flow response (strain-gauge plethysmography) induced in 10 hypertensive patients (aged 43.6 +/- 8.1 years, blood pressure 151.4 +/- 6.8/99.8 +/- 3.3 mmHg) by intrabrachial infusions of 0.15, 0.45, 1.5, 4.5, and 15 microg/100 ml per min acetylcholine and 5, 15, and 50 ng/100 ml per min bradykinin, two endothelium-dependent vasodilators, and 1, 2, and 4 microg/100 ml per min sodium nitroprusside, an endothelium-independent vasodilator. At baseline, vascular response was compared with that of 10 normotensive subjects (aged 42.4 +/- 6.6 years, blood pressure 118.4 +/- 6.1/77.8 +/- 3.4 mmHg).

RESULTS

Hypertensive patients had blunted (P < 0.01 or less) vasodilatations in response to infusions of acetylcholine (from 3.7 +/- 0.3 to 18.3 +/- 4.9 ml/100 ml per min) and bradykinin (from 3.7 +/- 0.4 to 15.8 +/- 2.6 ml/100 ml per min) compared with those of controls (from 3.6 +/- 0.3 to 25.3 +/- 5.2 ml/100 ml per min for acetylcholine and from 3.7 +/- 0.3 to 26.9 +/- 4.9 ml/100 ml per min for bradykinin) whereas the responses to infusion of sodium nitroprusside were similar (from 3.6 +/- 0.3 to 18.5 +/- 3.9 and from 3.6 +/- 0.3 to 16.4 +/- 1.8 ml/100 ml per min, respectively). Acute and prolonged lisinopril treatments significantly (P < 0.05 or less) improved vasodilatation in response to infusion of bradykinin (from 3.7 +/- 0.4 to 24.5 +/- 4.9 and from 3.7 +/- 0.3 to 22.1 +/- 4.9 ml/100 ml per min, respectively), but not in response to infusions of acetylcholine and of sodium nitroprusside. Chronic lisinopril treatment increased (P < 0.05) the response to infusions of not only bradykinin (from 3.5 +/- 0.5 to 27.6 +/- 5.3 ml/100 ml per min), but also of acetylcholine (from 3.5 +/- 0.5 to 27.8 +/- 8.0 ml/100 ml per min) and sodium nitroprusside (from 3.4 +/- 0.6 to 25.9 +/- 8.5 ml/100 ml per min). However, when the responses to infusions of acetylcholine and bradykinin were normalized with respect to that to infusion of sodium nitroprusside, only the vasodilatation in response to infusion of bradykinin was shown to have been increased by lisinopril treatment.

CONCLUSIONS

Administration of lisinopril to patients with essential hypertension can selectively increase vasodilatation in response to infusion of bradykinin.

Angiotensin-converting enzyme gene polymorphism is associated with endothelium-dependent vasodilation in never treated hypertensive patients

The response of the forearm vasculature to acetylcholine (7.5, 15, and 30 microg/min, each for 5 minutes) and sodium nitroprusside (0.8, 1.6, and 3.2 microg/min, each for 5 minutes) was evaluated in 32 never-treated hypertensive outpatients (17 men and 15 women, aged 43+/-7 years) and in 24 normotensive control subjects (14 men and 10 women, aged 42+/-6 years). Drugs were infused into the brachial artery, and forearm blood flow was measured by strain-gauge plethysmography. In both hypertensive and normotensive groups, a deletion (D)/insertion (I) polymorphism in intron 16 of the angiotensin-converting enzyme (ACE) gene was determined by polymerase chain reaction. The response to acetylcholine was significantly reduced in hypertensive patients versus control subjects: at the highest dose (30 microg/min), forearm blood flow was 13.9+/-6.3 mL x 100 mL tissue(-1) x min(-1) in hypertensives versus 27.1+/-9.7 mL x 100 mL tissue(-1) x min(-1) in the controls (P<.001); similarly, vascular resistance was 10.6+/-5.6 U in hypertensive patients and 4.9+/-1.9 U in normotensive subjects. In the hypertensive group, the patients with DD genotype showed significantly less endothelium-dependent vasodilation compared with ID+II genotypes (at the highest dose of acetylcholine, forearm blood flow was 12.1+/-4.2 versus 17.0+/-4.1 mL x 100 mL tissue(-1) x min(-1)) (P<.005). The vasodilator effect of sodium nitroprusside infusions was not statistically different in DD and ID+II hypertensive patients. In conclusion, our data suggest that ACE polymorphism affects endothelium-dependent vasodilation in hypertensive patients and confirm that hypertensive patients had a blunted response to the endothelium-dependent agent acetylcholine.

Renal endothelial function in humans

Animal experiments have shown extensively that the endothelial generation of nitric oxide participates in the regulation of renal haemodynamics and function, probably as a factor modulating the effects of endogenous vasoconstrictors. Although the endothelial function of the systemic vasculature is assessed through the vasodilatory effect of acetylcholine, only L-arginine infusion is available for studies of the influence of nitric oxide on the renal circulation in humans. In addition to peripheral vessels, L-arginine is a potent renal vasodilator, having no effect on the glomerular filtration rate; and the renal relaxation induced by L-arginine is markedly blunted in patients with essential hypertension. A few studies showing the renal vasoconstrictor effect of an inhibitor of nitric oxide synthesis have been reported.

The role of endothelium in human hypertension

Endothelium-derived nitric oxide is not only a potent vasodilator but also inhibits platelet aggregation, smooth muscle cell proliferation, monocyte adhesion and adhesion molecule expression. In several pathological conditions, such as human hypertension, nitric oxide availability is reduced. This alteration has been documented in the peripheral and coronary micro- and macrocirculation and in the renal circulation. The main mechanism leading to endothelial dysfunction is production of cyclooxygenase-dependent factors, including prostanoids and oxygen free radicals, which cause nitric oxide breakdown. Dysfunctional endothelium can be one of the main mechanisms causing vascular damage, in particular, atherosclerosis; hence, an important aim for antihypertensive treatment could reside not only in normalizing blood pressure values but also in reversing endothelial dysfunction. Available evidence indicates that different classes of antihypertensive compounds have different effects on endothelial dysfunction.

Relationship between endothelial function and fibrinolysis in early hypertension

Abnormalities in fibrinolysis, endothelial function, and glucose and lipid metabolism have been reported in hypertension. This study was conducted to examine the interrelationships between fibrinolytic factors, glucose and lipid metabolism, and endothelial function in hypertension. The effects of administering an angiotensin converting enzyme inhibitor, benazepril, were also examined. Blood levels of the following substances were measured in patients with borderline and mild hypertension (n=50, 51+/-19 years) and in age-matched controls (n=10): total cholesterol, triglycerides, tissue plasminogen activator activity and antigen, and plasminogen activator inhibitor type 1 activity and antigen. Insulin sensitivity was assessed by oral glucose tolerance test, and endothelial function was assessed by evaluating changes in diameter of the brachial artery during reactive hyperemia as observed by ultrasonography. Activities of tissue plasminogen activator and plasminogen activator inhibitor type 1 were both elevated in the hypertensive patients. Stepwise multiple regression analysis showed that plasminogen activator inhibitor type 1 antigen correlated with insulin sensitivity, total cholesterol levels, and triglycerides levels (P<.01). Endothelial function was negatively correlated with tissue plasminogen activator activity and antigen (P<.01). The chronic administration of benazepril (5-10 mg/d) for 20 weeks improved insulin sensitivity, endothelial function (6.6+/-3.4-->9.0+/-2.5%, P<.01), and tissue plasminogen activator activity and antigen. These results indicate that abnormalities in fibrinolysis are associated with endothelial dysfunction as well as disorders of glucose and lipid metabolism in patients with borderline and mild hypertension. The treatment of such patients with benazepril appeared to improve the impairment in fibrinolysis and endothelial dysfunction.

Impairment and restoration of nitric oxide-dependent vasodilation in cardiovascular disease

The generation of nitric oxide by the vascular endothelium maintains a continuous vasodilator tone that is essential for the regulation of blood flow and blood pressure. Nitric oxide also contributes to the control of platelet aggregation and has important antiatherogenic effects. These properties are mediated by the action of constitutive nitric oxide synthase and subsequent activation by nitric oxide of soluble guanylate cyclase. Impaired release of nitric oxide occurs in most animal and human models of hypertension, contributing to the increased peripheral resistance and most likely to the development of cardiovascular complications. Antihypertensive medications (angiotensin-converting enzyme [ACE] inhibitors and calcium channel blockers) appear to prevent the impairment of nitric oxide-mediated vasodilation in experimental hypertension, though in humans the data are not as clear. Reduced nitric oxide release appears therefore to be a consequence rather than a cause of high blood pressure, and the reduction in blood pressure per se is most important. In hyperlipidaemia, endothelium-dependent relaxations are reduced probably due to the inhibitory action of oxidized low-density lipoproteins on endothelium-dependent relaxations. Lipid-lowering strategies and, more recently, ACE inhibition have been demonstrated to improve nitric oxide dependent coronary vasodilation in hypercholesterolaemic patients with and without atheromatous coronary disease. Nitric oxide dependent vasodilation is also impaired in insulin- and non-insulin-dependent diabetes as well as in healthy aging. Endothelial dysfunction may be improved in non-insulin-dependent diabetes by administration of the antioxidants, supporting the hypothesis that nitric oxide inactivation by oxygen-derived free radicals contributes to abnormal vascular reactivity in diabetes.

Lacidipine restores endothelium-dependent vasodilation in essential hypertensive patients

Essential hypertension is characterized by impaired endothelium-dependent vasodilation. The present study was designed to test whether antihypertensive treatment with the calcium antagonist lacidipine can improve endothelium-dependent vasodilation in essential hypertensive patients. In 12 normotensive subjects (mean age, 47.8+/-8.6 years; blood pressure, 118.6+/-4.2/76.7+/-3.9 mm Hg) and 19 hypertensive patients (mean age, 49.4+/-10.2 years; blood pressure; 153.5+/-13.3/101.3+/-6.4 mm Hg), we studied forearm blood flow modifications (strain-gauge plethysmography) induced by intrabrachial infusion of acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg/100 mL per minute) and bradykinin (5, 15, and 50 ng/100 mL per minute), two endothelium-dependent vasodilators that act through different receptors and signal transduction pathways, and sodium nitroprusside (1, 2, and 4 microg/100 mL per minute), an endothelium-independent vasodilator. In essential hypertensive patients, vascular reactivity was repeated during prolonged (8 weeks of oral treatment at 6 mg/d) lacidipine administration and 2 weeks after withdrawal of chronic (32-week) treatment. Hypertensive patients showed significantly (P<.01) blunted vasodilation in response to acetylcholine (vascular resistance, 31.5+/-4.9 to 7.6+/-2.4 SU) and bradykinin (vascular resistance, 32.3+/-5.8 to 8.5+/-3.0 SU) compared with control subjects (vascular resistance: acetylcholine, 24.3+/-3.9 to 3.7+/-1.2 SU; bradykinin, 24.7+/-0.4 to 4.1+/-1.3 SU), whereas the response to sodium nitroprusside was similar. After either 8 or 32 weeks of lacidipine treatment, the vasodilation in response to acetylcholine (30.6+/-7.7 to 5.7+/-1.5 and 34.3+/-6.6 to 5.9+/-1.9 SU, respectively) and bradykinin (31.3+/-7.2 to 6.4+/-1.6 and 33.7+/-5.4 to 6.1+/-1.5 SU, respectively), but not to sodium nitroprusside, proved to be significantly (P<.05) increased compared with baseline. In essential hypertensive patients, oral treatment with lacidipine increased forearm vasodilation in response to acetylcholine and bradykinin, suggesting that this drug can improve endothelial function in patients with essential hypertension.

Cerebrovascular effects of nitric oxide manipulation in spontaneously hypertensive rats

1. Evidence that nitric oxide (NO) bioactivity is altered in chronic hypertension is conflicting, possibly as a result of heterogeneity in both the nature of the dysfunction and in the disease process itself. The brain is particularly vulnerable to the vascular complications of chronic hypertension, and the aim of this study was to assess whether differences in the cerebrovascular responsiveness to the NO synthase (NOS) inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), and to the NO donor 3-morpholinosydnonimine (SIN-1) might indicate one possible source of these complications. 2. Conscious spontaneously hypertensive (SHR) and WKY rats, were treated with L-NAME (30 mg kg-1, i.v.), 7-NI (25 mg kg-1, i.p.), (0.54 or 1.8 mg kg-1 h-1, continuous i.v. infusion) or saline (i.v.), 20 min before the measurement of local cerebral blood flow (LCBF) by the fully quantitative [14C]-iodoantipyrine autoradiographic technique. 3. With the exception of mean arterial blood pressure (MABP), there were no significant differences in physiological parameters between SHR and WKY rats within any of the treatment groups, or between treatment groups. L-NAME treatment increased MABP by 27% in WKY and 18% in SHR groups, whilst 7-NI had no significant effect in either group. Following the lower dose of SIN-1 infusion, MABP was decreased to a similar extent in both groups (around -20%). There was no significant difference in MABP between groups following the higher dose of SIN-1, but this represented a decrease of -41% in SHR and -21% in WKY rats. 4. With the exception of one brain region (nucleus accumbens), there were no significant differences in basal LCBF between WKY and SHR. L-NAME produced similar decreases in LCBF in both groups, ranging between -10 and -40%. The effect of 7-NI upon LCBF was more pronounced in the SHR (ranging from -34 to -57%) compared with the WKY (ranging from -14 to -43%), and in seven out of the thirteen brain areas examined there were significant differences in LCBF. 5. Following the lower dose of SIN-1, in the WKY 8 out of the 13 brain areas examined showed significant increases in blood flow compared to the saline treated animals. In contrast, only 2 brain areas showed significant increases in flow in the SHR. In the rest of the brain areas examined the effects of SIN-1 upon LCBF were less marked than in the WKY. 6. Infusion of the higher dose of SIN-1 resulted in further significant increases in LCBF in the WKY group (ranging between +30% and +74% compared to saline-treated animals), but no significant effects upon LCBF were found in the SHR. As a result, there were significant differences in LCBF between SIN-1-treated WKY and SHR in six brain areas. In most brain areas examined, cerebral blood flow in SHR following the higher dose of SIN-1 was less than that measured with the lower dose of SIN-1. 7. Despite comparable reductions in MABP (approximately 20%) in both groups, calculated cerebrovascular resistance (CVR) confirmed that the vasodilator effects of the lower dose of SIN-1 were significantly more pronounced throughout the brain in the WKY (ranging between -3% and -50%; median = -38%) when compared to the SHR (ranging between -10% and -36%; median = -26%). In the animals treated with the higher dose of SIN-1, CVR changes were broadly similar in both groups (median = -45% in WKY and -42% in SHR), but with the reduction in MABP in SHR being twice that found in WKY, this is in keeping with an attenuated blood flow response to SIN-1 in the SHR. 8. The results of this study indicate that NO-dependent vasodilator capacity is reduced in the cerebrovasculature of SHR. In addition, the equal responsiveness to a non-specific NOS inhibitor but an enhanced effectiveness of a specific neuronal NO inhibitor upon LCBF in the SHR could be consistent with an upregulation of the neuronal NO system.

Cutaneous vasodilation to acetylcholine in patients with essential hypertension

Endothelium-dependent vasodilation is reduced in the forearm of patients with essential hypertension. To evaluate whether endothelium-dependent vasodilation is also reduced in the skin microcirculation of patients with essential hypertension, we evaluated the effect of acetylcholine, an endothelium-dependent vasodilator, and sodium nitroprusside, an endothelium-independent vasodilator, on cutaneous and total forearm blood flow in normotensive subjects (n = 8) and matched patients with essential hypertension (n = 9). We infused acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg/100 ml forearm tissue/min) and sodium nitroprusside (1, 2, and 4 microg/100 ml forearm tissue/min) into the brachial artery, and we measured cutaneous blood flow (laser Doppler flowmeter) and muscle blood flow (strain-gauge venous plethysmography) modifications. Both the cutaneous and muscle blood flow increases induced by acetylcholine were reduced in patients with essential hypertension as compared with normotensive controls, whereas the skin and muscle vasodilation induced by sodium nitroprusside was similar in the two groups of patients. These data confirm the impairment of endothelium-dependent vasodilation in the muscle vascular bed of patients with essential hypertension and demonstrate the presence of endothelial dysfunction in skin microcirculation.

Effects of long-term antihypertensive treatment with lisinopril on resistance arteries in hypertensive patients with left ventricular hypertrophy

OBJECTIVE

To evaluate the effects of long-term antihypertensive therapy with the angiotensin converting enzyme inhibitor lisinopril on structural alterations and the endothelial function of small resistance arteries in hypertensive patients with left ventricular hypertrophy.

METHODS

Fourteen patients with left ventricular hypertrophy were treated for 3 years with a lisinopril-based regimen. Patients underwent an echocardiographic evaluation of left ventricular mass index at baseline, during the first and third years of treatment. At the end of the treatment period, subcutaneous small resistance arteries (obtained by biopsy of the subcutaneous fat from the gluteal region) were dissected and mounted on a micromyograph (Mulvany's technique); the media : lumen ratio was then calculated. Data obtained were compared with those observed for 14 untreated essential hypertensive patients and 14 normotensive subjects, age- and sex-matched.

RESULTS

In the present study, a significantly lower media : lumen ratio was observed in treated compared with untreated hypertensive patients, although it remained significantly higher than that in normotensive subjects. In treated hypertensive patients a significant reduction in clinic blood pressure was observed. However, their blood pressure remained significantly higher than that in normotensive subjects. Significant correlations between the media : lumen ratio and blood pressure, left ventricular mass index or changes in left ventricular mass index during treatment were observed. The response to acetylcholine administration was reduced in untreated hypertensives compared with that in normotensives. In patients treated with lisinopril, the vasodilatation obtained with the two higher doses of acetylcholine was greater than that in untreated hypertensives, thus suggesting an improvement of endothelial function.

CONCLUSIONS

Long-term therapy based on lisinopril was associated with a smaller media : lumen ratio in the subcutaneous small resistance arteries of hypertensive patients with left ventricular hypertrophy. Our retrospective study confirms previous findings obtained in prospective studies with other angiotensin converting enzyme inhibitors. Endothelial function was probably improved by lisinopril therapy.

Converting enzyme inhibitor improves forearm reactive hyperemia in essential hypertension

Endothelial function is known to be impaired in essential hypertensive patients. In this study, we examined whether antihypertensive drugs improve forearm vasodilatory response to reactive hyperemia in 26 patients with essential hypertension (62 +/- 2 years) without diabetes mellitus, hyperlipidemia, coronary heart disease, or cerebrovascular disease. Antihypertensive drugs were never given or were discontinued for at least 4 weeks before the study. Patients were treated with monotherapy of either temocapril (2 or 4 mg, n = 15) or amlodipine (2.5 or 5 mg, n = 11) for 6 months. Forearm blood flow was measured by strain-gauge plethysmography. Vasodilator response to the release of upper arm compression at 300 mm Hg for 5 minutes and to sublingual administration of nitroglycerin (0.3 mg) were assessed. Changes of forearm blood flow response to reactive hyperemia were significantly less in hypertensive patients (99 +/- 18%) than in age-matched normotensive control subjects (150 +/- 22%, P < .01, n = 39). Blood pressure (mm Hg) was similarly decreased by the treatment with temocapril (160 +/- 4/94 +/- 2 to 139 +/- 3/83 +/- 3, P < .001) or amlodipine (165 +/- 5/94 +/- 3 to 141 +/- 4/82 +/- 3, P < .001). Response to nitroglycerin was not changed by either drug. Forearm vasodilatory response to reactive hyperemia was improved by temocapril (102 +/- 20% to 168 +/- 25%, P < .01) but not by amlodipine (97 +/- 16% to 114 +/- 14%, NS). These results indicate that the treatment with the angiotensin-converting enzyme inhibitor temocapril improved forearm vasodilatory response to reactive hyperemia, suggesting its beneficial effect on endothelial function.

Angiotensin-converting enzyme inhibition restores flow-dependent and cold pressor test-induced dilations in coronary arteries of hypertensive patients

BACKGROUND

Cold pressor test (CPT)-induced and flow-dependent epicardial coronary artery dilations are impaired in patients with hypertension. ACE inhibition can attenuate sympathetic coronary constriction and potentiate or restore endothelium-dependent relaxations. This study was designed to determine whether the ACE inhibitor perindoprilat can restore normal coronary dilative responses in hypertensive patients.

METHODS AND RESULTS

Coronary vasomotor responses to CPT and to maximal increase of blood flow induced by papaverine were studied in 10 untreated patients with essential hypertension, no other risk factors, and angiographically normal coronary arteries before and after intravenous ACE inhibition by perindoprilat. Diameters of proximal and distal left anterior descending (LAD) and circumflex coronary arteries were measured by quantitative angiography. Estimates of coronary blood flow and resistance index were calculated with an intracoronary Doppler catheter in the distal LAD. Perindoprilat did not modify the hemodynamic responses to CPT and papaverine. In response to CPT, perindoprilat changed the epicardial coronary constriction (-8.4 +/- 5.8%, P < .001) into a significant dilation (+12.0 +/- 6.4%, P < .001). Perindoprilat significantly increased the coronary blood flow (from 33.7 +/- 10.0 to 57.9 +/- 20.5 mL/min, P < .01) and enhanced the decrease in coronary resistance (from 4.28 +/- 1.27 to 2.96 +/- 0.84 mm Hg.mL-1.min-1, P < .001) caused by CPT. Flow-dependent dilation of the proximal LAD was abolished in the control condition and was restored after perindoprilat (12.6 +/- 4.7%, P < .001).

CONCLUSIONS

ACE inhibition restored CPT-induced and flow-mediated coronary artery dilations in patients with essential hypertension. These results indicate that impaired coronary vasomotor responses may be reversible in recently diagnosed hypertension.

Impaired endothelial function with essential hypertension assessed by ultrasonography

The objective of this investigation was to evaluate the role of hypertension in endothelial function, changes in which are known to be an early event of atherosclerosis. We assessed endothelial function in 13 subjects with normal blood pressure and 13 subjects with essential hypertension who had never been treated for hypertension or hyperlipidemia and who had no history of smoking or coronary or cerebrovascular disease. B-mode ultrasonography was used to measure the diameter of the brachial artery. Endothelium-dependent dilatation was assessed as the change in diameter of the artery during reactive hyperemia. Endothelium-independent dilatation was evoked, as a control, by sublingual administration of isosorbide dinitrate. Despite similar ages and lipid and glucose levels in the study groups, endothelium-dependent dilatation was less in patients with hypertension (13.1% +/- 1.6%) than in subjects with normal blood pressure (18.5% +/- 1.9%) (p < 0.05), whereas isosorbide dinitrate-induced changes were similar. Systolic and diastolic blood pressure were significantly correlated with endothelium-dependent vasodilatation (r = -0.57 and r = -0.53, respectively) but not with the change by isosorbide dinitrate. These results suggest that endothelial dysfunction exists in patients with hypertension and precedes overt atherosclerotic disease.

Defective L-arginine-nitric oxide pathway in offspring of essential hypertensive patients

BACKGROUND

Essential hypertension is characterized by impaired endothelium-dependent vasodilation. The present study was designed to investigate whether this abnormality is a primary defect or a consequence of blood pressure increases.

METHODS AND RESULTS

In offspring of essential hypertensive patients (n = 34) and normotensive subjects (n = 30), we evaluated forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 micrograms.100 mL-1.min-1), an endothelium-dependent vasodilator, and sodium nitroprusside (1, 2, and 4 micrograms.100 mL-1.min-1), an endothelium-independent vasodilator. Minimal forearm vascular resistances also were calculated as the ratio between mean intra-arterial pressure and maximal forearm blood flow induced by forearm ischemia and hand exercise. Vasodilation to acetylcholine was significantly (P < .01) blunted in offspring of hypertensive patients compared with offspring of normotensive subjects, whereas the responses to sodium nitroprusside and minimal forearm vascular resistances were similar. In two subgroups of 14 offspring of essential hypertensive patients but not in 10 offspring of normotensive subjects, vasodilation to acetylcholine was increased by intra-brachial L-arginine (1 mumol.100 mL-1.min-1), the substrate for nitric oxide synthesis, whereas in the other 10 and 8 offspring of essential hypertensive patients and normotensive subjects, respectively, cyclooxygenase blockade by intra-brachial indomethacin (50 micrograms.100 mL-1.min-1) was ineffective.

CONCLUSIONS

Offspring of essential hypertensive patients are characterized by a reduced response to acetylcholine linked to a defect in the nitric oxide pathway, suggesting that an impairment in nitric oxide production precedes the onset of essential hypertension.

Effect of ACE inhibitors on endothelial dysfunction: unanswered questions and implications for further investigation and therapy

Experimental studies have suggested that angiotensin-converting enzyme (ACE) inhibitors may have an important role in blocking the progression of and/or reversing endothelial dysfunction. The extrapolation of these experimental studies to the clinical situation has, however, been disappointing. Studies of forearm-mediated endothelial vasodilatation in patients with hypertension with captopril, enalapril, and cilazapril have been negative. The finding of the Trial in Reversing Endothelial Dysfunction (TREND) that the administration of quinapril to normotensive patients with coronary artery disease in part restores endothelial-mediated coronary vasodilation, as assessed by intracoronary administration of acetylcholine, has important implications for future therapy and raises several important questions. The differences in the TREND and previous studies of ACE inhibitors on endothelial dysfunction in patients with coronary artery disease and hypertension. Although in general there has been a good correlation between endothelial dysfunction as assessed by forearm flow and coronary endothelial dysfunction as assessed by acetylcholine, these vascular beds may be affected differently by therapeutic interventions, especially with an ACE inhibitor, which may affect shear stress and angiotensin II formation in different vascular beds differently. Third, one needs to question whether the effect of quinapril on coronary endothelial dysfunction is a class effect or unique to quinapril. It will be necessary to test the effectiveness of other ACE inhibitors on coronary endothelial dysfunction in humans before concluding that the beneficial effects of quinapril are due to a class effect.

Pathogenetic factors in hypertension. Endothelial factors

In normotensive humans, endothelium modulates vascular tone mainly by the production of nitric oxide. In human essential hypertension the basal release of nitric oxide is reduced and forearm vasodilation to the endothelium-dependent agonists acetylcholine or bradykinin is blunted. Defective basal release of nitric oxide seems to be secondary to blood pressure increase while impaired agonist-evoked endothelium-dependent vasodilation is probably a primary phenomenum. This latter endothelial dysfunction seems to be caused by the simultaneous presence of an alteration in the L-arginine-nitric oxide pathway and the production of constrictor prostanoids. Defective nitric oxide production is already detectable in normotensive offspring of hypertensive patients and young essential hypertensive. In contrast, vasoconstrictor prostanoid production seems to be associated with aging. In essential hypertensive patients, although only scanty data are available, chronic effective pharmacological treatment seems to restore impaired basal production of nitric oxide but does not improve vascular response to endothelial agonists.

Effects of cilazapril on vascular structure and function in essential hypertension

Hypertension is associated with an altered design of resistance vessels and decreased endothelium-dependent vasodilator response to acetylcholine. A role of angiotensin II in both defects is suggested by animal experiments in which angiotensin-converting enzyme inhibition reverted structural and functional changes. We investigated the effects of 20 weeks of therapy with the angiotensin-converting enzyme inhibitor cilazapril (5 mg twice daily) on the endothelium-dependent response to brachial artery infusions of acetylcholine and the endothelium-independent vascular relaxation after sodium nitroprusside in 22 subjects with mild to moderate essential hypertension. In addition, we measured minimal forearm vascular resistance (ratio of mean arterial pressure and forearm blood flow after heating, ischemia, and ischemic exercise) as an indirect estimate of vascular structure. Cilazapril decreased blood pressure (151 +/- 14/99 +/- 7 mm Hg during placebo to 138 +/- 17/89 +/- 8 mm Hg after cilazapril treatment, P<.01) and baseline (42.2 +/- 12.6 to 37.1 +/- 10.6 U, P<.05) and minimal (3.0 +/- 1.1 to 2.4 +/- 0.7 U, 15.9 +/- 20.2%; P<.05) forearm vascular resistances. The change in minimal forearm vascular resistance was unrelated to age, duration of hypertension, or changes in blood pressure. Sodium nitroprusside increased forearm blood flow from 2.6 +/- 1.0 to 11.4 +/- 5.9 mL/min per 100 mL and acetylcholine to 21.5 +/- 17.8. Both responses did not change after cilazapril. The data provide indirect evidence that cilazapril therapy may improve vascular structure in human hypertension. The lack of relationship between vascular and blood pressure changes would be compatible with experimental evidence supporting a role for angiotensin II in the development and regression of vascular changes, but this needs further study. Therapy with cilazapril for 20 weeks, like other antihypertensive therapy, does not seem to influence endothelial vasodilator function in humans to a significant degree.

Antihypertensive therapy and arterial function in experimental hypertension

1. Alterations in the function of the endothelium and arterial smooth muscle may be important in the establishment of hypertension. Thus, the possible favorable influences of blood pressure-lowering agents on vascular responsiveness may be important in the chronic antihypertensive actions of these compounds. 2. A number of reports have suggested that ACE inhibitors can improve arterial function in hypertension, whereas the knowledge about the vascular effects of other antihypertensive drugs, like beta-blockers, calcium channel blockers, and diuretics remains rather limited. 3. In this article, the effects of antihypertensive therapy on arterial function in human and experimental hypertension are reviewed.

Nitric oxide release from kidneys of hypertensive rats treated with imidapril

To examine whether endothelial dysfunction in hypertension is reversible or not, we studied the effects of imidapril, an angiotensin-converting enzyme inhibitor, on nitric oxide release in stroke-prone spontaneously hypertensive rats (SHR) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. After a 4-week treatment with imidapril (1 or 10 mg/d SC) or vehicle, acetylcholine-induced vasodilation and nitric oxide release in the isolated kidneys were determined. Nitric oxide release was measured by a chemiluminescense assay. Imidapril lowered blood pressure in stroke-prone SHR in a dose-dependent manner. Untreated stroke-prone SHR exhibited significantly attenuated responses to acetylcholine (10(-8) mol/L) of both renal perfusion pressure (stroke-prone SHE 42 +/- 4% versus Wistar-Kyoto rats [WKY] 58 +/- 4% [mean +/- SE], P < .01) and nitric oxide release (stroke-prone SHR +7.6 +/- 2.1 versus WKY +29.7 +/- 9.7 fmol/min per gram of kidney wt, P < .01). Imidapril at 10 mg/d significantly increased acetylcholine-induced renal vasodilation and nitric oxide release in stroke-prone SHR (renal perfusion pressure, 56 +/- 3%; nitric oxide release, +27.1 +/- 6.4 fmol/min per gram of kidney wt; both P < .01 versus stroke-prone SHR treated with vehicle). On the other hand, imidapril neither decreased blood pressure nor changed nitric oxide release induced by acetylcholine in DOCA-salt hypertensive rats. Staining for endothelial nitric oxide synthase and brain nitric oxide synthase was clearly detected in the kidneys of both stroke-prone SHR and WKY, whereas staining intensity was weaker in DOCA-salt hypertensive rats. Inducible nitric oxide synthase immunoreactivity was barely noticeable in any type of rat. Thus, imidapril restored endothelial damage by pressure-dependent mechanisms. Most of the nitric oxide detected in the perfusate seemed to be derived from constitutive nitric oxide synthase.

Evidence for a multifactorial process involved in the impaired flow response to nitric oxide in hypertensive patients with endothelial dysfunction

The assessment of endothelial function in hypertensive patients receiving acetylcholine has revealed conflicting results. Whether an impaired flow response to acetylcholine is explained solely by a diminished endothelial synthesis of nitric oxide (NO) remains unclear as yet. In the present study, we tested the hypothesis that mechanisms other than reduced NO synthesis contribute to the hypertension-associated impairment of endothelium-dependent vasodilation. Therefore, the dilatory response to endogenous and exogenous NO was measured in resistance arteries and cutaneous microvessels in the forearm circulation of 12 normotensive individuals and 17 hypertensive patients. In addition, the overall dilatory capacity was assessed by peak flow during reactive hyperemia after 3 minutes of ischemia. Forearm blood flow was quantified by venous occlusion plethysmography at rest, during application of the NO donor sodium nitroprusside, and during stimulation of endogenous NO synthesis by acetylcholine and bradykinin. Blood flow velocity in the cutaneous microvasculature was measured with laser-Doppler flowmetry in parallel. Resting forearm flow was comparable in both groups (3.1 +/- 0.2 and 3.4 +/- 0.2 mL.min-1.100mL-1 tissue), whereas blood pressure and thus peripheral vascular resistance was significantly elevated in hypertensive compared with normotensive subjects. Hyperemic peak flow was significantly blunted in hypertensive patients. Sodium nitroprusside, acetylcholine, and bradykinin increased flow in a dose-dependent manner to a comparable extent in the control group (13.3 +/- 0.8, 13.6 +/- 1.3, and 14.6 +/- 0.7 mL.min-1.100mL-1 tissue, respectively). In contrast, in hypertensive patients maximum increase in resting flow was significantly reduced (sodium nitroprusside, -36%; acetylcholine, -44%; and bradykinin, -56%). The flow response after stimulation of endogenous NO synthesis by bradykinin was significantly more blunted compared with that of exogenous NO after application of sodium nitroprusside. In the cutaneous microvasculature, bradykinin-induced increases in blood flow velocity were selectively impaired in hypertensive patients, whereas flow response to acetylcholine was preserved. Thus, we conclude that in arterial hypertension endothelium-dependent, NO-mediated dilation of resistance arteries and cutaneous microvessels of the forearm vasculature is heterogeneously impaired, depending on the type of endothelial receptor stimulated. Furthermore, the present data suggest that in hypertensive patients the impairment of NO-dependent dilation of resistance arteries is caused by at least three different mechanisms: (1) a reduced endothelial synthesis of NO due to either a disturbed signal-transduction pathway and/or a reduced activity of NO synthase, (2) an accelerated NO degradation within the vessel wall, and (3) alterations in the vessel architecture resulting in an overall reduced dilatory capacity of resistance arteries.

Antihypertensive therapy prevents endothelial dysfunction in chronic nitric oxide deficiency. Effect of verapamil and trandolapril

The objective of this study was to examine the effects of long-term antihypertensive therapy on blood pressure and vascular responses of resistance arteries during prolonged inhibition of nitric oxide synthesis. Four groups of 6-week-old Wistar-Kyoto rats were treated with either placebo as controls or N omega-nitro-L-arginine methyl ester (L-NAME) alone or in combination with verapamil or with trandolapril. Drugs were given orally for 6 weeks or short-term in vitro to vessels obtained from untreated rats. Endothelium-dependent and -independent relaxations as well as contractions were studied in isolated perfused mesenteric and renal arteries with an arteriograph. Kidney nitric oxide synthase activity was also evaluated. Verapamil and trandolapril prevented the increase in systolic blood pressure and the blunted acetylcholine-induced relaxations that occurred with L-NAME treatment without improving the nitric oxide synthase activity. Both antihypertensive regimens also normalized sensitivity to sodium nitroprusside, which was enhanced by L-NAME. In contrast, short-term in vitro preincubation with verapamil or trandolaprilat in the presence of L-NAME did not improve the impaired relaxations to acetylcholine. Long-term but not short-term therapy with a calcium antagonist or angiotensin-converting enzyme inhibitor improved the blunted endothelium-dependent relaxations in nitric oxide-deficient hypertension. These findings strongly suggest that the role of other vasodilator systems, which normally do not regulate vascular tone, is enhanced with long-term but not short-term treatment with these drugs. These observations emphasize the potential importance of these treatments in the management of hypertension in which nitric oxide production is diminished.

Contrasting effect of antihypertensive treatment on the renal response to L-arginine

We assessed the renal hemodynamic response to L-arginine infusion (30 g within 60 minutes) in normotensive subjects, patients with never-treated essential hypertension, and hypertensive patients controlled by long-term (more than 2 years) treatment with or without an angiotensin-converting enzyme inhibitor. The renal vasodilator response to L-arginine observed in normotensive subjects (15 +/- 4% increase in effective renal plasma flow) was abolished in untreated hypertensive patients and restored only in the group treated by angiotensin-converting enzyme inhibition. In the whole population a positive correlation between the change in effective renal plasma flow and the change in urinary cGMP was obtained. It is suggested that abnormalities of the renal nitric oxide pathway not corrected by increased availability of L-arginine and reversible only on long-term treatment by angiotensin-converting enzyme inhibition may underlie the abnormal renal resistance observed in essential hypertension.

Is endothelial dysfunction reversible?

To date, the published database concerning the impact of therapy on endothelial function in essential hypertension and hypercholesterolemia is small and incomplete. Chronic antihypertensive therapy had not yet been proven to restore endothelial function in patients with essential hypertension. In contrast, chronic lipid-lowering therapy is effective in restoring endothelial function of the coronary and peripheral circulation in patients with hypercholesterolemia. A beneficial effect was already documented after 3 months of therapy with fluvastatin but full restoration may last more than 1 year.

Aging and endothelial function in normotensive subjects and patients with essential hypertension

BACKGROUND

Experimental data from normotensive and hypertensive animals indicate that aging is associated with impaired endothelium-dependent relaxations to acetylcholine, and this possibility appears to be confirmed in the human coronary artery. In the present study, we evaluated the effect of age on endothelial responsiveness in the forearm vessels of either normotensive control subjects or essential hypertensive patients.

METHODS AND RESULTS

Within the normotensive or hypertensive group (n = 53 and n = 57, respectively), subjects were selected with similar blood pressure, plasma cholesterol, and glucose values, and hypercholesterolemic subjects, diabetics, and smokers were excluded. We evaluated forearm blood flow (by strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 micrograms/100 mL per minute), an endothelium-dependent vasodilator, and sodium nitroprusside (1, 2, and 4 micrograms/100 mL per minute), an endothelium-independent vasodilator. Acetylcholine caused a dose-dependent vasodilation that was significantly (P < .01) lower in essential hypertensive patients than in normotensive control subjects. However, a significant negative correlation was observed between acetylcholine-induced vasodilation and patient age in both normotensive (r = -.86, P < .001) and hypertensive (r = -.85, P < .001) patients. In contrast, vasodilation to sodium nitroprusside was similar in normotensive control subjects and essential hypertensive patients with a poorer inverse correlation with patient age (normotensive control subjects, r = -.37; hypertensive patients, r = -.36) compared with acetylcholine.

CONCLUSIONS

The present data indicate that there is a blunted response to acetylcholine with advancing age in both normotensive control subjects and essential hypertensive patients, suggesting that aging is associated with reduced endothelium-dependent vasodilation in humans.