Reduction of plasma and urinary vasopressin during treatment of severe hypertension by captopril

Patterns of Renal Function in Hypertension Due to Unilateral Renal Artery Occlusion

We performed renal function studies in dogs with chronic renovascular hypertension produced by complete occlusion of a renal artery. In addition, we evaluated in anesthetized dogs the acute effects of a novel angiotensin converting enzyme inhibitor, CGS 16,617, on renal function and plasma neurohormones (epinephrine, norepinephrine and vasopressin) 4 weeks after initiation of 2 kidney, 1 clip hypertension. CGS 16,617 effectively decreased blood pressure in renal hypertensive animals. This response was associated with suppression of angiotensin II indicating effective converting enzyme inhibition. In the non-clipped kidney, acute administration of CGS 16,617 increased effective renal plasma flow but not glomerular filtration rate and urinary sodium excretion. In the clipped kidney, CGS 16,617 caused no change in any parameter of renal function. Plasma norepinephrine, epinephrine and vasopressin were unaffected by administration of CGS 16,617. These studies showed that chronic occlusion of a renal artery does not result in renal infarction because of a compensatory increase in the amount of blood provided through capsular collateral vessels. The collateral circulation which has developed in the clipped kidney explains the lack of a converting enzyme inhibitor effect.

Changes in pulmonary hemodynamics predict benefits in exercise capacity after ACE inhibition in patients with mild to moderate congestive heart failure

Several causes may affect the efficacy of angiotensin-converting enzyme (ACE) inhibitors in congestive heart failure (CHF). The present study was undertaken to identify what factors might predict benefits in exercise capacity after ACE inhibition in 22 patients with mild to moderate CHF. All patients underwent hemodynamic evaluation before and following an oral dose of quinapril (20 mg). They were then treated daily with 20 mg of quinapril and underwent exercise stress test off-drugs 1 day and 6 months later. Patients were grouped according to their relative changes in vascular resistances after quinapril: Group A (n = 15) showed a greater decrease in pulmonary vascular resistance (PVR) than in systemic vascular resistance (SVR) (% delta PVR/% delta SVR > 1). The opposite occurred in Group B (n = 7). Comparison of pretreatment baseline features revealed that the two groups had similar biochemical and hormonal variables, cardiac index, and SVR. Conversely, Group A patients had higher (p < 0.05) pulmonary artery pressure and PVR compared with Group B patients. Following quinapril, Group A patients showed a greater (p < 0.05) increase in cardiac index than Group B patients, despite a similar reduction in SVR. Accordingly, 1-day drug treatment significantly (p < 0.001) increased exercise duration in Group A (+29%), but not in Group B patients (+7%). Benefits in exercise capacity were still significant (p < 0.001) 6 months later.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in vasopressin mechanisms in captopril-treated spontaneously hypertensive rats

The effects of lifetime captopril treatment on vasopressin (VP) were assessed in spontaneously hypertensive rats (SHR). Pregnant and nursing dams were treated with oral Captopril (100 mg/kg/day). After weaning, the pups were maintained on Captopril (50/kg/day) for 19-20 wks. Blood pressures of Captopril-treated SHR were in the normotensive range and significantly lower (p less than .001) than SHR control rats. Control and Captopril-treated SHR were perfused and brains were sectioned for immunohistochemical staining with a polyclonal antibody directed against vasopressin (VP). Compared to control SHR, Captopril-treated rats displayed decreased VP-like immunoreactivity in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Captopril treatment also selectively decreased the number of brightly labeled cell bodies in the SON and PVN and reduced VP-like labeling in the axons of the neurons in these nuclei. Concurrent with a decrease in VP-like immunoreactivity, Captopril treatment reduced plasma VP levels (RIA) (p less than 0.01, Captopril, 5.6 +/- 0.5 pg/ml; control, 11.8 +/- 2.2 pg/ml). Scatchard analysis of 3H-VP binding indicated that Captopril treatment increased the number but not the affinity of VP receptors in the hypothalamus and brain stem of SHR. These results suggest that in SHR oral Captopril treatment attenuates the synthesis and release of VP, an effect that may contribute to the blood pressure lowering effect of converting enzyme inhibitors.

Chronic therapy for congestive heart failure with benazepril HCl, a new angiotensin converting enzyme inhibitor

Benazepril HCl is an orally effective angiotensin converting enzyme (ACE) inhibitor previously shown to have significant acute hemodynamic benefits in patients with congestive heart failure. In this study, 21 patients with New York Heart Association Class III or IV congestive heart failure were treated with 2 to 15 mg of benazepril HCl as a single daily oral dose for 28 days to determine the clinical and hemodynamic value of chronic therapy. Each patient underwent clinical evaluation during the 28-day period, as well as invasive hemodynamic studies on the first two and last two days of the trial. Plasma ACE activity and aldosterone levels fell significantly and renin levels rose after therapy. Benazepril HCl produced significant (p less than 0.01) reductions in arterial pressure and systemic vascular resistance, with corresponding increases in cardiac output and decreases in pulmonary artery wedge pressure. Responses after 28 days of therapy were equivalent to those after the initial doses. Clinical effects included reduced rest, exertional and paroxysmal nocturnal dyspnea, as well as reduced peripheral edema. Only one patient developed symptomatic orthostatic hypotension. Thus, benazepril HCl, given once daily, is an effective and well tolerated oral agent for the chronic treatment of advanced congestive heart failure.

Baroreceptor reflex in elderly essential hypertensives: effect of chronic inhibition of angiotensin converting enzyme

Baroreflex function and plasma angiotensin II (Ang II) were examined in five elderly and five young or middle-aged essential hypertensive patients before and after enalapril treatment. Baroreflex sensitivity (BS) during blood pressure (BP) elevation by phenylephrine (PE) but not during BP reduction by sodium nitroprusside (SNP) was significantly attenuated in the elderly compared with the younger group, while plasma Ang II concentration was not different between the two groups. Enalapril treatment reduced BP without significant changes in heart rate and plasma norepinephrine in both groups, suggesting a leftward shift of barofunction curve. It also increased the BS in some cases in each group. However, plasma Ang II was not significantly reduced during enalapril treatment. The changes in BS did not correlate with changes in plasma Ang II. These results suggest that BS may be attenuated with increasing age independent of plasma Ang II and that ACE inhibitor influences the set point of the barofunction curve and BS by different mechanisms.

Angiotensin-converting enzyme inhibitors

There is convincing evidence that ACE inhibitors, alone or in combination with a diuretic, effectively lower blood pressure in patients with all grades of essential or renovascular hypertension and that they are of particular benefit as adjunctive therapy in patients with congestive heart failure. The hemodynamic, hormonal and clinical effects of the presently available ACE inhibitors, captopril and enalapril, are comparable and their side effect profiles are extremely favorable. One important difference between the two oral ACE inhibitors, however, is their pharmacokinetics; enalapril's action is slower to begin and is of longer duration. Compared with other agents, ACE inhibitors offer important advantages, among them an improved feeling of well being. It is, therefore, expected that ACE inhibitors will gain greater acceptance by patients and physicians in the future.

Influence of nifedipine and enalapril on osmoregulation of vasopressin

To determine whether calcium fluxes and angiotensin II influence osmoregulation of vasopressin (AVP) secretion, the effects of the calcium antagonist nifedipine and of the converting enzyme inhibitor enalapril on the AVP response to an osmotic load were compared to those of a placebo in seven normal female subjects. Plasma and urinary AVP were measured before and during a 3-h infusion of 2.5% hypertonic saline. Nifedipine (10 mg orally 2 h before and 10 mg at the start of the infusion) increased heart rate but did not change blood pressure. The changes in free water clearance and in urinary AVP induced by hypertonic saline under nifedipine were greater than in the control test, but the slope and the intercept of the regression line of plasma AVP upon plasma osmolality were not significantly different. Enalapril (10 mg 3 h before the infusion) did not change heart rate or blood pressure. Free water clearance and urinary AVP did not differ from the control test, but the slope of the regression line was less steep. These slight modifications of the response to an osmotic load suggest that calcium fluxes and angiotensin II only exert a limited influence on AVP osmoregulation in normal females.

Pharmacology of converting enzyme inhibitors

Angiotensin converting enzyme inhibitors were developed to prevent the in vivo generation of angiotensin II and thereby to reduce peripheral vasoconstriction. However, these compounds exert some additional effects that may or may not be angiotensin dependent. These include potential sodium diuresis, bradykinin accumulation, prostaglandin release, blunting of sympathetic activity, parasympathomimetic actions, central effects, redistribution of blood flow toward some particularly important organs. Only the comprehensive assessment of the many complex interactions that exist between the renin-angiotensin and several other regulatory systems reveals the complete therapeutic profile of this class of pharmacologic agents.

The acute haemodynamic effects of quinapril, a new non-sulfhydryl angiotensin converting enzyme inhibitor, in patients with severe congestive cardiac failure

This study investigates the acute haemodynamic effects of Quinapril (CI-906) a new non-sulphydryl angiotensin converting enzyme inhibitor in 15 patients with refractory congestive cardiac failure. There were 14 males and 1 female mean age 59.5 years. After administration of Quinapril there was a significant reduction in mean arterial pressure (MAP) from 93.1 to 79 mmHg, systemic vascular resistance (SVR) from 1887 to 1349 dyn s cm-5 and PCW from 27.3 to 15.3 mmHg. This was accompanied by an increase in CO from 3.7 to 4.71/min, cardiac index (CI) from 1.97 to 2.51/min/m2 and Stroke volume index from 21.1 to 28.7 ml/m2. There was no significant change in heart rate (HR), right atrial pressure (RAP), or pulmonary vascular resistance. The peak effect on pulmonary capillary wedge pressure (PCW) and cardiac output (CO) occurred at 75-120 min after Quinapril administration. The maximum effect on mean arterial pressure (MAP) occurred slightly later at 120-150 min. SVR and CI exhibited 2 periods of peak effects, at 90 and 180 min. This time course is very similar to that observed in studies on the acute effects of Captopril. The significant improvement in haemodynamic measurements acutely, following administration of Quinapril 5 mg orally, suggests that this drug is worthy of further study in the management of patients with refractory congestive cardiac failure, in particular its long term effects.

Effect of captopril on renal haemodynamics and the renin-angiotensin-aldosterone and osmoregulatory systems in essential hypertension

The effect of captopril on renal plasma flow (RPF), glomerular filtration rate (GFR), plasma concentrations of renin, angiotensin II (Ang II), aldosterone (Aldo) and arginine vasopressin (AVP), serum osmolality (Sosm), free water clearance (CLH2O), fractional urinary excretion of electrolytes and blood pressure (BP), was examined in 10 patients with moderate essential hypertension. Placebo plus furosemide was given for 6 weeks, followed by a 6-week period on captopril and furosemide. The renin-angiotensin-aldosterone system was partly blocked by captopril, resulting in a 18% fall in BP. GFR was reduced by 8% during captopril treatment, whereas RPF remained unchanged. Water loading-induced suppression of Ang II and AVP was inhibited by captopril therapy. Without affecting BP in the placebo period, water loading almost abolished the captopril-induced reduction in BP. It is concluded that non-acute captopril treatment of moderates essential hypertension reduces GFR slightly, possibly by producing dilatation of efferent arterioles. The antipressor effect of captopril is lessened during volume expansion, which may be secondary to reduced activity of the renin-angiotensin-aldosterone and osmoregulatory systems.

Effects of enalapril alone, and in combination with hydrochlorothiazide, on renin-angiotensin-aldosterone, renal function, salt and water excretion, and body fluid composition

Enalapril is a new, oral, long-acting nonsulfhydral angiotensin converting enzyme inhibitor. Thirty-nine patients with primary hypertension were entered into a randomized, double-blind protocol to assess the efficacy of enalapril (10 to 20 mg bid), hydrochlorothiazide (25 to 50 mg bid), or combined drug therapy. Enalapril, either alone or in combination with hydrochlorothiazide, effectively controlled blood pressure. Enalapril monotherapy was associated with an increase in plasma renin activity and a decrease in angiotensin II concentration; in patients with an initial inulin clearance less than or equal to 80 mL/min/1.73 m2, inulin and para-aminohippurate clearances were markedly improved, without producing adverse effects on salt and water excretion or body fluid composition. Combination therapy was associated with a marked increase in plasma renin activity; however, only those patients with an initial inulin clearance less than or equal to 80 mL/min/1.73 m2 demonstrated suppression of angiotensin II concentration and marked improvement in inulin and para-aminohippurate clearances. These observations suggest that enalapril, either alone or in combination with a diuretic, has the potential to reverse renal function abnormalities encountered in the hypertensive state.

Hemodynamic and clinical significance of the pulmonary vascular response to long-term captopril therapy in patients with severe chronic heart failure

Exercise capacity in patients with left heart failure is closely related to the performance of the right ventricle and the pulmonary circulation. To determine the significance of changes in pulmonary resistance during long-term vasodilator therapy, hemodynamic studies were performed before and after 1 to 3 months of treatment with captopril in 75 patients with severe chronic left heart failure. Patients were grouped according to the relative changes in pulmonary and systemic resistances during long-term therapy: patients in Group I (n = 24) showed greater decreases in pulmonary arteriolar resistance (PAR) than in systemic vascular resistance (SVR) (% delta PAR/% delta SVR greater than 1.0), whereas patients in Group II showed predominant systemic vasodilation (% delta PAR/% delta SVR less than 1.0). Despite similar changes in systemic resistance, patients in Group I showed greater increases in cardiac index, stroke volume index and left ventricular stroke work index (p less than 0.01 to 0.001) but less dramatic decreases in mean systemic arterial pressure (p less than 0.02) than did patients in Group II. Despite similar changes in left ventricular filling pressure, patients in Group I showed greater decreases in mean pulmonary artery and mean right atrial pressures (p less than 0.02 to 0.01) than did patients in Group II. Pretreatment variables in Groups I and II were similar, except that plasma renin activity was higher (8.7 +/- 2.1 versus 3.0 +/- 0.6 ng/ml per h) and serum sodium concentration was lower (133.1 +/- 0.9 versus 137.1 +/- 0.6 mEq/liter) in Group II than in Group I (both p less than 0.05). Both groups improved clinically after 1 to 3 months, but symptomatic hypotension occurred more frequently in Group II than in Group I (36 versus 8%) (p less than 0.005). These findings indicate that changes in the pulmonary circulation modulate alterations in both right and left ventricular performance during the treatment of patients with left heart failure. Hyponatremic patients are likely to experience symptomatic hypotension with captopril because they are limited in their ability to increase cardiac output as a result of an inadequate pulmonary vasodilator response to the drug.

Usefulness of plasma renin activity in predicting haemodynamic and clinical responses and survival during long term converting enzyme inhibition in severe chronic heart failure. Experience in 100 consecutive patients

The relation between plasma renin activity before treatment and the haemodynamic and clinical responses to converting enzyme inhibition was determined in 100 consecutive patients with severe chronic heart failure who were treated with captopril or enalapril. Initial doses of captopril produced significant increases in cardiac index and decreases in left ventricular filling pressure, mean arterial pressure, mean right atrial pressure, heart rate, and systemic vascular resistance that varied linearly with the pretreatment value for plasma renin activity. In contrast, there was no relation between the pretreatment activity and the magnitude of haemodynamic improvement after 1-3 months of treatment with the converting enzyme inhibitors, and, consequently, a similar proportion of patients with a high (greater than 6 ng/ml/h; greater than 4.62 mmol/l/h), intermediate (2-6 ng/ml/h; 1.54-4.62 mmol/l/h), and low (less than 2 ng/ml/h; less than 1.54 mmol/l/h) pretreatment value improved clinically during long term treatment (64%, 60%, and 64% respectively). Long term survival after one, two, and three years was similar in the three groups. Estimating the degree of activation of the renin-angiotensin system by measuring pretreatment plasma renin activity fails to predict the long term haemodynamic or clinical responses to converting enzyme inhibitors in patients with severe chronic heart failure, and thus appears to be of limited value in selecting those patients likely to benefit from treatment with these drugs.

A cooperative multicenter study of captopril in congestive heart failure: hemodynamic effects and long-term response

The acute hemodynamic effects, long-term clinical efficacy, and safety of the oral angiotensin-converting enzyme inhibitor, captopril, were assessed in a multicenter cooperative study of 124 patients with heart failure resistant to digitalis and diuretics. The cardiac status of most patients was deteriorating prior to the study. Favorable acute hemodynamic effects consistently occurred with captopril. Maximal mean percentage increases in cardiac index, stroke index, and stroke work index were, respectively, 35%, 44%, and 34%. Systemic and pulmonary vascular resistances were each decreased by approximately 40%, as were the filling pressures of the right and left heart. Infusion of nitroprusside in some of the same patients to an end point of a pulmonary capillary wedge pressure of 12 to 18 mm Hg (equivalent to that after captopril) revealed no significant difference in the effect of either drug on the other hemodynamic parameters. Recatheterization after 8 weeks of captopril therapy revealed sustained hemodynamic changes. Significant and sustained improvements in clinical status were observed in most patients as measured by changes in New York Heart Association (NYHA) functional classification and exercise tolerance times. Seventy-nine percent of patients for whom there were adequate NYHA class data improved. Twenty percent remained unchanged and 1% deteriorated. Those patients who had both pretreatment and post-treatment exercise stress testing exhibited a highly significant mean increase in exercise tolerance times of 34% (317 +/- 32 seconds pretreatment to 425 +/- 34 seconds, final measurement). There was no evidence of tachyphylaxis over an 18-month period.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of angiotensin converting enzyme inhibitors in essential and renal hypertension. Effects of captopril and enalapril on renin-angiotensin-aldosterone, renal function and hemodynamics, salt and water excretion, and body fluid composition

Among the many generic classes of drugs currently being used for the treatment of hypertension, few, following long-term therapy, improve or correct the underlying renal function and hemodynamic abnormalities encountered in patients with sustained hypertension. This review focuses on the renal effects of the angiotensin converting enzyme inhibitors captopril and enalapril. Each drug is discussed in terms of its short- and long-term effects on the renin-angiotensin-aldosterone system, renal function and hemodynamics, salt and water excretion, and body fluid composition. Data are presented that demonstrate that enalapril, used alone or in combination with diuretic therapy, has the unique ability to control hypertension, to improve glomerular filtration rate and effective renal plasma/renal blood flow, and to decrease renal vascular resistance, without producing adverse effects on salt and water excretion or body fluid composition. If the safety of enalapril is confirmed in long-term studies, the drug will clearly assume a prominent role as either first- or second-step (in combination with a diuretic) therapy in the treatment of hypertension.

Osmoregulation and renal effects of vasopressin in normal and mildly hypertensive subjects

A 2-hr 0.85 M hypertonic saline infusion was administered to ten normotensive volunteers and ten mildly hypertensive subjects to compare in these two groups the osmoregulation of vasopressin and the effect of this hormone on BP. No significant alteration in BP was observed in either group, despite markedly enhanced vasopressin levels. Significant positive correlations between plasma vasopressin (AVP) and plasma osmolality (POsm) were demonstrated in the controls (AVP = -70 + 0.25 POsm, r = 0.68, P less than 0.0001) and in the hypertensive group (AVP = -46 + 0.16 POsm, r = 0.59, P less than 0.0001). However, the vasopressin response to the osmotic stimulus was buffered in the hypertensive subjects; the slope of the regression line between plasma vasopressin and plasma osmolality was less steep in hypertensive subjects than in normotensive subjects (0.16 vs. 0.25, P less than 0.018). During the saline infusion the renal parameters were identical in the two groups. Finally, in mild hypertension, the osmoregulation of vasopressin was preserved but buffered and renal sensitivity to this hormone was normal. An osmotically induced physiological increase in vasopressin did not raise BP in either normotensive or mildly hypertensive subjects.

Role of the renin-angiotensin system in the control of vasopressin and ACTH secretion during the development of renal hypertension in dogs

Experiments were performed to determine if the activation of the renin-angiotensin system that occurs during the development of two-kidney, one clip Goldblatt hypertension in dogs is accompanied by increases in vasopressin and adrenocorticotrophic hormone (ACTH) secretion. Following renal artery constriction, there were marked increases in arterial blood pressure, plasma renin activity (PRA), and plasma angiotensin II (AII) concentration. These changes were accompanied by an increase in plasma vasopressin concentration during the second week following constriction, and there were significant correlations between plasma vasopressin concentration and PRA (r = 0.57, p less than 0.001), and between plasma vasopressin concentration and plasma AII concentration (r = 0.59, p less than 0.001). In contrast, plasma corticosteroid concentration, used as an index of changes in ACTH secretion, did not change significantly. Acute blockade of the renin-angiotensin system with captopril or saralasin produced the expected changes in blood pressure, PRA, and plasma AII concentration but did not decrease plasma vasopressin or corticosteroid concentrations. These results indicate that during the development of renal hypertension in dogs, there may be an interaction between the renin-angiotensin system and vasopressin, but not between the renin-angiotensin system and the pituitary-adrenal axis. They also show that the antihypertensive action of captopril in this experimental model is not mediated via suppression of vasopressin, ACTH, or corticosteroid secretion.