Captopril-induced changes in large arteries in essential hypertension

ACE (Angiotensin-Converting Enzyme) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals in Chronic Hypertension

Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and important for stroke outcome. We previously showed LMAs from SHRs (spontaneously hypertensive rats) were vasoconstricted compared with normotensive Wistar rats. Here, we investigated mechanisms by which hypertension causes LMA vasoconstriction. SHRs were treated with the ACE (angiotensin-converting enzyme) inhibitor captopril, an Ang II (angiotensin II)-independent antihypertensive agent hydralazine, or vehicle for 5 weeks in drinking water (n=8/group). A group of Wistar rats (n=8) had regular drinking water served as controls. Blood pressure was measured twice weekly by tail-cuff. LMAs were isolated and studied under pressurized conditions. Vasoreactivity of LMAs, including myogenic responses, reactivity to Rho-kinase inhibitor Y-27632, and nitric oxide were measured. Both captopril and hydralazine lowered blood pressure in SHRs similar to Wistar. However, only captopril normalized LMA increased tone compared with untreated SHRs (15±2% versus 50±3%; P<0.01) that was similar to Wistar (16±2%) but not hydralazine (38±6%; P>0.05). Vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared with Wistar (28±3% versus 81±4%; P<0.01) that was restored by captopril (84±5%; P<0.01) and partially hydralazine (59±4%). LMAs from all groups constricted similarly to NOS (NO synthase) inhibition; however, the vasodilatory response of LMAs to the nitric oxide donor sodium nitroprusside was impaired in SHRs compared with Wistar rats (29±4% versus 80±2%; P<0.01) that was restored by captopril (84±4%; P<0.01), not hydralazine (38±8%; P>0.05). These results suggest that ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs that could improve stroke outcome by increasing collateral perfusion.

Central arterial aging and the epidemic of systolic hypertension and atherosclerosis

The structure and function of central arteries change throughout the lifetime of humans and animals. Since atherosclerosis and hypertension are prevalent in epidemic proportion among older persons, it is reasonable to hypothesize that specific mechanisms that underlie the arterial substrate that has been altered by an "aging process" are intimately linked to arterial diseases. Indeed, recent studies reveal a profile of arterial cell and matrix properties that emerges with advancing age within the grossly normal appearing aortic wall of both animals and humans. This profile is proinflammatory, and is manifested by intimal infiltration of fetal cells, increased production of angiotensin II (Ang II)-signaling pathway molecules, eg, matrix metalloproteases (MMPs), and monocyte chemoattractant protein (MCP-1), transforming growth factor B1 (TGF-beta1), enhanced activation of MMPs, TGF-beta, and NADPH oxidase, and reduced nitric oxide (NO) bioavailability. This profile is similar to that induced at younger ages in experimental animal models of hypertension or atherosclerosis. In humans, this proinflammatory state, which occurs in the absence of lipid deposition, appears to be attributable to aging, per se. Other well known human risk factors, eg, altered lipid metabolism, smoking, and lack of exercise, interact with this arterial substrate that is altered by aging and render the aging human artery fertile soil for facilitation of the initiation and progression of arterial diseases. Therapies to reduce or retard this age-associated proinflammatory state within the grossly appearing arterial wall central arteries, in addition to slowing arterial aging, per se, may have a substantial impact on the quintessential age-associated arterial diseases of our society.

Effect of angiotensin II blockade on central blood pressure and arterial stiffness in subjects with hypertension

In hypertension, the blood pressure curve may be divided into two sets of components. The first set is mean arterial pressure, steady flow, and vascular resistance, thus acting on small arteries; the second set refers to large arteries, hence to pulse pressure, arterial stiffness, and wave reflections. The angiotensin-converting enzyme (ACE) inhibitor perindopril not only reduces mean arterial pressure but also acts specifically on pulse pressure. The effect on pulse pressure predominates on central rather than peripheral (brachial) large arteries, reducing aortic stiffness and most wave reflections. Such hemodynamic changes are not observed with standard β-blockade, which reduces aortic stiffness and brachial systolic and pulse pressure but not central pulse pressure and wave reflections. In hypertensive subjects, perindopril and other ACE inhibitors seem to predict more consistently the reduction of cardiovascular events, mainly of cardiac origin, than standard β-blockers alone. This effect is associated with the important biochemical finding that mechanotransductions of angiotensin and β-blockade are markedly different, acting in the former specifically on the α5β1 integrin complex and on the fibronectin ligand of arterial vessels.

Lisinopril reverses left ventricular hypertrophy through improved aortic compliance

We treated with nifedipine or lisinopril 38 essential hypertensive patients with left ventricular hypertrophy. The study had a single-blind crossover design; nifedipine or lisinopril was given for the first 24 weeks, and then patients were crossed over to the other antihypertensive agent for another 24 weeks. Both nifedipine and lisinopril significantly decreased mean arterial pressure to the same extent. Although lisinopril decreased left ventricular mass index more rapidly than nifedipine, 48 weeks of antihypertensive treatment with nifedipine or lisinopril reduced the extent of left ventricular hypertrophy to the same level. Stepwise multiple linear regression analysis revealed that the reversal of left ventricular hypertrophy may be mainly due to a reduction in mean arterial pressure during the 24-week nifedipine treatment and due to an improvement of aortic compliance during the lisinopril treatment. Both nifedipine and lisinopril are effective in the reversal of hypertensive left ventricular hypertrophy; however, the agents have disparate actions on hemodynamic factors.

Arterial hemodynamics in human hypertension. Effects of angiotensin converting enzyme inhibition

Previous studies have shown some distinct hemodynamic alterations in essential hypertension, including increased resistance, wave reflections, and pulse wave velocity and decreased systemic compliance. These abnormalities are completely normalized by nonspecific smooth muscle dilation with nitroprusside but not by combined alpha- and beta-adrenergic blockade. The renin-angiotensin system, acting possibly via both circulating and local tissue effects, is thought to play an important role in essential hypertension, so its role in the altered hemodynamics deserves careful investigation. A hypertensive patient group was compared with a normotensive group similar in age, body size, and proportion of men and women. During diagnostic cardiac catheterization, ascending aortic micromanometer pressures and electromagnetic flows were measured in the baseline state. Intravenous captopril of a sufficient dosage (11 mg) to normalize blood pressure then was given to the hypertensive patients while measurements were repeated. From the pressures and flows, aortic input impedance, wave reflection magnitude, and compliance were computed. In the hypertensive group, the important hemodynamic alterations consisted of increased peripheral resistance, first zero crossing of aortic impedance phase angle, and wave reflections and decreased systemic compliance. Captopril had a pronounced hemodynamic effect. It normalized blood pressure, resistance, and impedance phase angle zero crossing. Compliance, although increased substantially by captopril, was still slightly lower than normotensive levels. The magnitude of wave reflections, although substantially lowered by angiotensin converting enzyme inhibition, was still persistently greater than normal. The present results, together with those previously reported, demonstrate that a complex interplay of factors underlies the increased smooth muscle tone in essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of inhibitors of angiotensin-converting enzyme on regional hemodynamics

Inhibitors of angiotensin-converting enzyme (ACE) exert favorable regional hemodynamic effects at various sites. In patients with essential hypertension, ACE inhibitors reduce renal vascular resistance while enhancing renal blood flow, glomerular filtration rate, and acute and sustained natriuresis. Whereas these agents may either reduce or have no effect on hepatic blood flow, they are associated with reduced splanchnic resistance. ACE inhibitors reduce total peripheral resistance and may maintain limb blood flow. In normal subjects, they augment blood flow to skeletal muscle and skin and reduce peripheral resistance in vessels supplying these regions. ACE inhibitors appear to exert a vasodilatory effect on large arteries as well as arterioles. Dilatation is often accompanied by significant improvements in arterial compliance, possibly due to direct effects of the renin-angiotensin system on the arterial wall. Reduction of blood pressure is generally not accompanied by reduced cerebral blood flow. Enhanced tissue effects of newer ACE inhibitors such as quinapril may result in improved regional hemodynamic effects.

Large artery function in patients with chronic heart failure. Studies of brachial artery diameter and hemodynamics

BACKGROUND

Although progressive chronic congestive heart failure (CHF) is associated with elevated systemic vascular resistance and increased impedance to ventricular outflow, the contribution of changes in large artery function has not been well documented in humans.

METHODS AND RESULTS

We studied 45 patients with a broad range of clinical severity of CHF and compared noninvasive measurements of brachial artery diameter, flow, and pulse wave velocity with 22 normal controls of similar age. In CHF, mean arterial pressure was lower than in controls (85 +/- 1 versus 93 +/- 2 mm Hg, p less than 0.001), as were brachial artery diameter (4.07 +/- 0.10 versus 4.53 +/- 0.09 mm, p less than 0.001), flow (40.9 +/- 4.1 versus 70.9 +/- 11.5 ml.min-1, p less than 0.02), compliance (1.29 +/- 0.12 versus 2.00 +/- 0.18 cm4.dyne-1.10(-7), p less than 0.002), and conductance (0.49 +/- 0.05 versus 0.76 +/- 0.13 units, p = 0.06). Limb vascular resistance (40.2 +/- 5.0 versus 20.5 +/- 3.1 units, p less than 0.001) and pulse wave velocity (10.6 +/- 0.5 versus 9.2 +/- 0.4 m.sec-1, p less than 0.03) were higher than in controls. Brachial artery diameter was progressively lower than in controls as severity of CHF increased (New York Heart Association class II, 4.47 +/- 0.23 mm, p = NS; class III, 4.05 +/- 0.10 mm, p less than 0.05; class IV, 3.71 +/- 0.28 mm, p less than 0.05). Similar changes were observed for arterial compliance (class II, 1.76 +/- 0.32 cm4.dyne-1.10(-7), p = NS; class III, 1.21 +/- 0.13 cm4.dyne-1.10(-7), p less than 0.05; class IV, 0.95 +/- 0.10 cm4.dyne-1.10(-7), p less than 0.05). While the lower arterial pressure and flow might be expected to passively reduce arterial diameter, this would be associated with a reduced pulse wave velocity and improved arterial compliance, yet the opposite was observed. Differences in large artery function were not likely caused by underlying atherosclerosis alone, because patients with dilated cardiomyopathy and patients with ischemic heart disease of the same sex, age, left ventricular ejection fraction, and exercise treadmill duration had similar changes in large artery function.

CONCLUSIONS

We conclude that alterations in brachial artery function are present in patients with moderate and severe CHF. The observed reduction in arterial compliance, if present diffusely throughout the arterial tree, could increase left ventricular end-systolic stress directly and through increased velocity of reflected pressure waves from the periphery.

Drug-induced modification of vascular structure: effects of antihypertensive drugs

It has long been realized that hypertension causes alterations in the peripheral vasculature, with the arterial wall becoming thicker and the lumen relatively smaller. This is particularly true in small resistance arteries, but larger vessels are also affected. The precise mechanisms remain to be determined, although it is highly likely that growth-promoting autacoids are involved as well as mechanical forces. Numerous studies of hypertension in animal models and a few in hypertensive humans have tried to establish the reversibility of these changes after successful lowering of blood pressure. Too few data are available to form firm conclusions, but thiazides and hydralazine-like vasodilators appear to have only a minimal effect on the vasculature. On the other hand, angiotensin-converting enzyme inhibitors are clearly effective, and alpha-blockers may be active. However, it is difficult to derive even tentative conclusions from the available information on calcium antagonists and beta-blockers. These results are discussed in the context of future therapeutic and investigative approaches.

Effect of celiprolol on large and small arteries of the forearm circulation in hypertensive patients

Celiprolol, a new highly cardioselective beta blocker, also has direct vasodilating properties. Since the noninvasive echo Doppler technique applied to the forearm circulation (brachial artery) allows the differentiation of arteriolar vasodilation (revealed by the increasing arterial blood flow velocity) from vasodilation of large arteries (shown by an increase in arterial diameter), it seems important to study the site of celiprolol's vasodilating effect. Thirty-five hypertensive patients, (21 male, 14 female; mean age, 59 +/- 11, range 42-79 years) were treated with increasing doses of celiprolol, 200 and 400 mg, over 15 days. The duplex echo Doppler technique (Aloka 7.5 M Hz probe) was used before and during each celiprolol dose period. Statistical analysis was performed by Student's paired t test. It was observed that celiprolol significantly increases the brachial artery diameter in a dose-dependent manner, and also increases the blood flow velocity (not being direct dose-related). Since the increase in diameter was clear with a higher dose, a dose-dependent increase in blood volume, a decrease in peripheral resistance, and an increase in compliance followed. Since the higher dose of celiprolol did not further reduce blood pressure (BP) in comparison to the lower dose, and a dose-dependent increase in arterial diameter and compliance occurred and a vasodilating effect of celiprolol on arterial wall ensued that was not related to BP. In conclusion, in the doses used, celiprolol dilates both arterioles and large arteries, but the mechanism of action needs to be clarified.

New insights and new approaches for the treatment of essential hypertension: selection of therapy based on coronary heart disease risk factor analysis, hemodynamic profiles, quality of life, and subsets of hypertension

The pharmacologic therapy of mild primary hypertension (diastolic blood pressure less than 105 mm Hg) has effectively reduced hypertensive arteriolar end organ disease such as cerebrovascular accidents, congestive heart failure, and nephropathy, but there has been no convincing evidence that coronary heart disease (CHD) or its complications, acute myocardial infarction or angina, have been reduced. The risks of therapy with certain antihypertensive drugs may outweigh their treatment benefits as it relates to CHD. The optimal treatment strategy should be to reduce all CHD risk factors, reverse the hemodynamic abnormalities present by lowering the systemic vascular resistance (SVR), preserving cardiac output (CO) and perfusion, and to select the best antihypertensive drug for concomitant medical diseases or problems while maintaining a good quality of life. Antihypertensive drugs that have favorable or neutral effects on CHD risk factors include alpha blockers, calcium channel blockers, central alpha agonists, and angiotensin-converting enzyme inhibitors. On the other hand, diuretics and beta blockers without intrinsic sympathomimetic activity have unfavorable effects on many CHD risk factors. Baseline and serial evaluation of the effects of these drugs on serum lipids, lipid subfractions, glucose, uric acid, electrolytes, exercise tolerance, left ventricular hypertrophy, blood pressure, SVR, CO, perfusion, concomitant diseases, and side effects is necessary to evaluate overall cardiovascular risk.

Clinical implications for therapy: possible cardioprotective effects of ACE inhibition

1. The circulating and tissue renin-angiotensin systems (RAS) contribute importantly to cardiovascular homeostasis. Systemic and/or local activation of the RAS is seen in many pathological conditions of the cardiovascular system (e.g. hypertension and congestive heart failure). Increased angiotensin production participates in the pathophysiology of these and other disease states. Accordingly, inhibitors of the renin angiotensin system have a broad spectrum of therapeutic efficacy. 2. Angiotensin-converting enzyme (ACE) inhibitors are effective antihypertensive agents that do not adversely affect serum lipid levels. In addition, they reduce left ventricular hypertrophy. 3. ACE inhibitors cause coronary vasodilation and reduce ventricular work and wall stress. They have been shown to reduce experimental infarct size and to increase anginal threshold in humans. 4. After experimental or human myocardial infarction that results in significant left ventricular dysfunction, ACE inhibitors prevent ventricular dilatation and development of congestive heart failure, and may improve survival. 5. ACE inhibitors can prevent ventricular fibrillation and contractile impairment (stunned myocardium) associated with reperfusion injury after experimental myocardial ischaemia. 6. ACE inhibitors reduce preload and afterload, improve exercise capacity, reduce ventricular arrhythmias, and improve patient survival in clinical cardiac failure. 7. Taken together, inhibition of the RAS may potentially result in primary as well as secondary protective effects on the cardiovascular system.

Placebo-controlled comparison of captopril, atenolol, labetalol, and pindolol in hypertension complicated by intermittent claudication

In a six month placebo-controlled cross-over trial twenty patients with hypertension and peripheral arterial disease were randomised to captopril 25 mg twice daily, atenolol 100 mg once daily, labetalol 200 mg twice daily, or pindolol 10 mg twice daily for one month. Although all treatments were equally effective at lowering blood pressure, pain-free and maximum walking distances on a treadmill were decreased by atenolol, labetalol, and pindolol, but not by captopril. Post-exercise calf blood flow availability was impaired by atenolol, labetalol, and pindolol, but not by captopril. Despite ancillary characteristics of cardioselectivity, intrinsic sympathomimetic activity, or combination with alpha-blockade, beta-blockers seem to impair the lower limb circulation in such patients, whereas captopril seems to preserve it, possibly by maintaining the collateral blood supply.

Pharmacokinetics, converting enzyme inhibition and peripheral arterial hemodynamics of ramipril in healthy volunteers

The effects of a 10 mg dose of ramipril, a new angiotensin I converting enzyme (ACE) inhibitor, on systemic blood pressure, heart rate, brachial artery blood flow, brachial artery diameter, carotid artery blood flow, carotid artery diameter, forearm vascular resistance, plasma ACE and renin activities and plasma aldosterone were investigated. Ramipril's effects in 6 healthy volunteers on a normal sodium diet were compared with those of placebo over a 24-hour period after oral drug intake in an open cross-over trial. Ramipril inhibited plasma ACE activity, an effect that peaked at 3 to 4 hours and persisted up to at least 24 hours. Plasma renin activity increased from 4 to 12 hours after drug intake and plasma aldosterone was slightly decreased. Systemic blood pressure in the supine position was slightly decreased between 6 and 8 hours after drug intake but heart rate remained unaffected. Ramipril significantly increased brachial artery blood flow, brachial artery diameter and carotid artery blood flow and decreased forearm vascular resistance between 3 and 8 hours after drug administration. These peripheral arterial vasodilating effects were more marked in the muscular resistance vessels and affected both large arteries and arterioles in the brachial vascular territory. A correlation was found between the log of plasma concentrations of ramipril diacid metabolite and the drug-induced plasma ACE activity inhibition and increase in brachial artery blood flow. There was also a correlation between these 2 latter effects. A plasma ACE activity inhibition of 80% was required to induce significant increases in brachial artery blood flow and carotid artery blood flow.

Captopril + hydrochlorothiazide 24 h ambulatory monitoring effects

The purpose of this study was to evaluate over a 24 h period the antihypertensive effect of captopril 50 mg + hydrochlorothiazide (HCTZ) 25 mg once a day in mild to moderate hypertension. Ambulatory recordings over 24 h of the blood pressure using the Spacelabs system were performed, at the end of a 15-day placebo period and after giving captopril + HCTZ for 45 days. Captopril + HCTZ significantly decreased (P less than 0.001) systolic and diastolic blood pressures for both the diurnal period (8 h to 22 h) and the nocturnal period (22 h to 8 h). No change in heart rate was observed. For further analysis, the mean hour values of blood pressure and heart rate were calculated. A constant decrease of the systolic and diastolic blood pressure throughout the 24 h was obtained after captopril + HCTZ without any change in heart rate and in nyctohemeral variations. The study provided evidence that, in patients with mild to moderate essential hypertension, captopril + HCTZ once a day decreased systolic and diastolic blood pressure all day long without any change in the heart rate and the blood pressure nyctohemeral cycle.

Changes in arterial distensibility produced by converting enzyme inhibitors in hypertensive humans

Converting enzyme inhibitors enhance arterial compliance in hypertensive humans. The enhancement is due not only to an increase in arterial diameter and volume but also to an increase in arterial distensibility. The latter effect reflects the drug action on arterial smooth muscle tone rather than the lower stretch due to the blood pressure reduction. The improvement in the buffering function of large arteries in hypertensives may contribute to produce a more important decrease in systolic pressure and a better reversion of cardiac hypertrophy.

Captopril for the treatment of patients with hypertension and peripheral vascular disease

Many epidemiological studies have shown up the frequent association of arterial hypertension (HT) with atherosclerosis of different localizations. However, many of the drugs used to treat HT are contraindicated in patients with peripheral vascular disease (PVD), because they cause unfavorable metabolic changes or vasoconstriction. The aim of the present study was to assess the effect of a proven hypotensive drug, captopril, on the peripheral circulation. The drug appeared to be effective in improving blood flow to lower limbs, prolonging the pain. Free interval and increasing the angle/arm arterial pressure index.