Efficacy of oral angiotensin-converting enzyme inhibition with captopril therapy in severe chronic normotensive congestive heart failure

Application of a physiologically based pharmacokinetic model in predicting captopril disposition in children with chronic kidney disease

Over the last several decades, angiotensin-converting enzyme inhibitors (ACEIs) have been a staple in the treatment of hypertension and renovascular disorders in children. One of the ACEIs, captopril, is projected to have all the benefits of traditional vasodilators. However, conducting clinical trials for determining the pharmacokinetics (PK) of a drug is challenging, particularly in pediatrics. As a result, modeling and simulation methods have been developed to identify the safe and effective dosages of drugs. The physiologically based pharmacokinetic (PBPK) modeling is a well-established method that permits extrapolation from adult to juvenile populations. By using SIMCYP simulator, as a modeling platform, a previously developed PBPK drug-disease model of captopril was scaled to renally impaired pediatrics population for predicting captopril PK. The visual predictive checks, predicted/observed ratios (ratio_pred/obs), and the average fold error of PK parameters were used for model evaluation. The model predictions were comparable with the reported PK data of captopril in mild and severe chronic kidney disease (CKD) patients, as the mean ratio_pred/obs C_max and AUC_0-t were 1.44 (95% CI 1.07 - 1.80) and 1.26 (95% CI 0.93 - 1.59), respectively. The successfully developed captopril-CKD pediatric model can be used in suggesting drug dosing in children diagnosed with different stages of CKD.

Should ACE inhibitors and ARBs be used in combination in children?

The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in a host of renal and cardiovascular functions. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), drugs that disrupt RAAS function, are effective in treating hypertension and offer other renoprotective effects independent of blood pressure (BP) reduction. As our understanding of RAAS physiology and the feedback mechanisms of ACE inhibition and angiotensin receptor blockade have improved, questions have been raised as to whether combination ACEI/ARB therapy is warranted in certain patients with incomplete angiotensin blockade on one agent. In this review, we discuss the rationale for combination ACEI/ARB therapy and summarize the results of key adult studies and the limited pediatric literature that have investigated this therapeutic approach. We additionally review novel therapies that have been developed over the past decade as alternative approaches to combination ACEI/ARB therapy, or that may be potentially used in combination with ACEIs or ARBs, in which further adult and pediatric studies are needed.

Effects of N-acetylcysteine on nitroglycerin-induced relaxation and protein phosphorylation of porcine coronary arteries

We investigated the effects of the sulfhydryl-donor, N-acetylcysteine (NAC), on nitroglycerin (NTG)-induced relaxation of the vascular smooth muscle. Addition of histamine to isolated porcine coronary arteries induced an initial rapid contraction followed by a gradual decrease in tonic contraction. NTG applied to the coronary artery strips before histamine caused relaxation of the histamine-induced rapid (3 min) and tonic (48 min) contraction. The inhibition of the tonic contraction by NTG was less at 48 min than at 3 min. Application of NAC (NTG-NAC) enhanced the relaxing effects of NTG on the histamine-induced tonic contraction rather than the acute contraction. In phosphorylation studies, changes in the phosphorylation of an intermediate filament, desmin, were parallel with changes in contraction in NTG-treated and NTG-NAC samples at 48 min. These phosphorylation changes of desmin at 48 min, which might be responsible for tonic phase contraction, were more extensive than those of myosin light chain (MLC) phosphorylation at 3 min, which might be responsible for acute contraction. These results suggest that treatment with the sulfhydryl donor, NAC, inhibited the phosphorylation of desmin associated with the enhancement of NTG-induced relaxation, which might be related to the mechanisms of recovery from NTG tolerance by sulfhydryl groups.

Exertional dyspnea in heart failure: a symptom unrelated to pulmonary function at rest or during exercise. Duke University Clinical Cardiology Studies (DUCCS) Exercise Group

BACKGROUND

Exertional dyspnea is a common symptom in patients with heart failure, and the mechanisms responsible for the symptom are unknown. The purpose of this study was to identify factors responsible for the symptom of exertional dyspnea in patients with heart failure.

METHODS

Resting pulmonary-function tests and maximal cardiopulmonary exercise tests were performed in 71 patients with New York Heart Association functional class II-IV symptoms (mean ejection fraction 30.6%; mean age, 68 years).

RESULTS

The severity of dyspnea at peak exercise, which patients rated as 3 to 10 on a 1 to 10 severity scale, did not correlate with rest or exercise hemodynamic, spirometric, or metabolic variables, including peak oxygen uptake (VO2), minute ventilation (Ve), and respiratory rate, or with derived variables including Ve/VO2, Ve/VCO2, and the dyspnea index (Ve/maximum voluntary ventilation). Additionally, these variables did not differ between patients who reported limitation of exercise by dyspnea and those who were limited by fatigue.

CONCLUSIONS

The symptom of exertional dyspnea in patients with heart failure is not determined by abnormalities in ventilatory function or demand.

Improvement in the mechanical efficiency of walking: an explanation for the "placebo effect" seen during repeated exercise testing of patients with heart failure. Duke University Clinical Cardiology Studies (DUCCS) Exercise Group

To determine the mechanism responsible for the "placebo effect" seen during serial exercise testing of patients with heart failure, we examined metabolic variables for 81 patients who underwent five baseline exercise tests as part of a multicenter drug trial. The patients were 50 men and 31 women with a mean ejection fraction of 30.1% and a mean age of 69 years. From test 1 to 2, the exercise time increased from 419 +/- 140 to 462 +/- 130 seconds before it reached a plateau over the next three tests. Metabolic measurements at test 1 and test 3 revealed no change in peak oxygen consumption ( 1119 +/- 376 to 1105 +/- 346 ml/min). Maximum heart rate, systolic blood pressure, ventilation, and respiratory exchange ratio also were unchanged. The onset of the anaerobic threshold was delayed from 211 +/- 81 to 238 +/- 93 seconds, but there was no change in oxygen consumption at the anaerobic threshold (810 +/- 222 to 795 +/- 220 ml/min). At a predetermined submaximal level, oxygen consumption, ventilation, and respiratory exchange ratio all decreased to a statistically significant degree. These results indicate that a rapid increase in the mechanical efficiency of walking contributes to the placebo effect among patients with heart failure during serial exercise testing and is independent of changes in conditioning or motivation.

Systemic, pulmonary, brachial, renal and hepato-splanchnic hemodynamic effects of spirapril in severe congestive heart failure

The effects of a single oral dose (6 mg) of the angiotensin-I converting enzyme inhibitor, spirapril, on systemic, pulmonary and regional (brachial, renal, hepato-splanchnic) hemodynamics as well as on biological parameters investigating the renin-angiotensin-aldosterone and sympathetic nervous systems were studied over a 24-hour period in eight patients with severe congestive heart failure (CHF). As compared to pretreatment values, spirapril significantly decreased mean arterial (-19%, peak effect), right atrial (-42%), mean pulmonary arterial (-38%) and pulmonary capillary wedge (-46%) pressures. Spirapril significantly decreased heart rate (-14%) and increased stroke volume index (+43%) thus resulting in a slight increase in cardiac index. All these effects were maximal between 2.5 and 4 h. Brachial artery diameter (+12%) and brachial (+41%) and renal (+36%) blood flows increased significantly whereas brachial (-41%) and renal (-36%) vascular resistances decreased significantly. All these effects were usually maximal between 1 and 2.5 h. Hepato-splanchnic hemodynamics were not drug-affected. Spirapril significantly inhibited plasma converting enzyme activity (-96% at 4 h), increased plasma renin activity (+505% at 4 h), and decreased plasma aldosterone (-46% at 24 h), norepinephrine (-31% at 24 h) and atrial natriuretic factor (-33% at 7 h). Thus, in severe CHF, acute administration of spirapril, 6 mg orally, exerts both arterial and venous vasodilating properties and improves both the systemic and regional hemodynamics and the biological status of the patients.

Adverse effects of enalapril in the Studies of Left Ventricular Dysfunction (SOLVD). SOLVD Investigators

In the Studies of Left Ventricular Dysfunction (LVD), enalapril or placebo was administered in a double-blind fashion to 6797 participants with ejection fraction < or = 0.35. During 40 months' average follow-up, 28.1% of participants randomized to enalapril reported side effects compared with 16.0% in the placebo group (p < 0.0001). Enalapril use was associated with a higher rate of symptoms related to hypotension (14.8% vs 7.1%, p < 0.0001), azotemia (3.8% vs 1.6%, p < 0.0001), cough (5.0% vs 2.0%, p < 0.0001), fatigue (5.8% vs 3.5%, p < 0.0001), hyperkalemia (1.2% vs 0.4%, p = 0.0002), and angioedema (0.4% vs 0.1%, p < 0.05). Side effects resulted in discontinuation of blinded therapy in 15.2% of the enalapril group compared with 8.6% in the placebo group (p < 0.0001). Thus enalapril is well tolerated by patients with LVD; however, hypotension, azotemia, cough, fatigue, and other side effects result in discontinuation of therapy in a significant minority of patients.

Splanchnic venous pressure-volume relation during experimental acute ischemic heart failure. Differential effects of hydralazine, enalaprilat, and nitroglycerin

BACKGROUND

Vasodilator drugs have variable effects on veins and arteries. However, direct measurements of their effects on the splanchnic veins, perhaps the most important volume reservoir, have not been reported. We assessed the effect of acute heart failure and the subsequent administration of hydralazine, enalaprilat, and nitroglycerin on the splanchnic venous pressure-volume relation in intact dogs.

METHODS AND RESULTS

Experimental acute ischemic heart failure was induced in 19 splenectomized dogs by microsphere embolization of the left main coronary artery. Embolization was repeated until left ventricular end-diastolic pressure (LVEDP) reached 20 mm Hg and cardiac output decreased by 50%. The splanchnic vascular pressure-volume relation was determined by radionuclide plethysmography during the control stage, after acute heart failure had been established, and after administration of a vasodilator (hydralazine, enalaprilat, or nitroglycerin) at a dose sufficient to reduce mean aortic pressure by approximately 20%. Induction of acute heart failure was associated with a decrease in the splanchnic vascular volume from 100% to 86 +/- 2% and an increase in LVEDP from 6 +/- 1 to 21 +/- 1 mm Hg (P < .001). There was a parallel leftward shift of the splanchnic vascular pressure-volume curve. After the administration of hydralazine, enalaprilat, and nitroglycerin, the splanchnic vascular volumes increased from 86% to 88 +/- 3%, 96 +/- 3%, and 113 +/- 3%, respectively (P = NS, P < .01, and P < .001, respectively, versus heart failure). After drug administration, the LVEDPs were 18 +/- 2, 16 +/- 1, and 13 +/- 1 mm Hg (P = NS, P < .05, and P < .001, respectively, versus heart failure).

CONCLUSIONS

Acute heart failure was associated with a parallel leftward shift of the splanchnic venous pressure-volume relation (venoconstriction). Splanchnic (systemic) venoconstriction may in part explain the increased LVEDP during acute heart failure by displacement of blood to the central compartment. Subsequently administered enalaprilat and, to a greater degree, nitroglycerin produced splanchnic venodilation, thereby lowering LVEDP. Hydralazine had no significant effect on the splanchnic veins and only a modest effect on LVEDP. In this model, splanchnic capacitance changes appear to modulate change in left ventricular preload.

Cardiac hypertrophy, aortic compliance, peripheral resistance, and wave reflection in end-stage renal disease. Comparative effects of ACE inhibition and calcium channel blockade

BACKGROUND

We wished to assess the respective roles of the antihypertensive and blood pressure (BP)-independent effects of antihypertensive drugs on arterial hemodynamics and left ventricular hypertrophy (LVH) in end-stage renal disease (ESRD) patients.

METHODS AND RESULTS

In a double-blind study, 24 ESRD patients with LVH were randomized to 12 months' administration of either the angiotensin-converting enzyme (ACE) inhibitor perindopril (n = 14) or the calcium channel blocker nitrendipine (n = 10). Repeated measurements of the following parameters were performed: BP (mercury sphygmomanometry), left ventricular mass (LVM, echocardiography), cardiac output (aortic cross-section and velocity integral), total peripheral resistance (cardiac output and mean BP), aortic and large-artery compliance (pulse wave velocity, Doppler flowmeter), and arterial wave reflections (augmentation index, applanation tonometry). Radioimmunoassay was used to determine plasma renin activity, aldosterone, and plasma catecholamine levels. Two-way (time-treatment) ANOVA for repeated measures was used for statistical analysis. Perindopril and nitrendipine induced significant and similar decreases in BP, total peripheral resistance (P < .001), aortic and arterial pulse wave velocities (P < .001), and arterial wave reflections (P < .01). At baseline, the two groups had LVH mostly due to increased LV end-diastolic diameter (LVEDD) (perindopril, 54.3 +/- 1.4 and nitrendipine, 54.3 +/ 2.4 mm) with near-normal mean LV wall thickness (perindopril, 11.4 +/- 0.3 and nitrendipine, 11.2 +/- 0.4 mm). A decrease in LVM was observed only in patients receiving perindopril (from 317 +/- 18 to 247 +/- 21 g) (time-treatment interaction, P = .036). Nitrendipine had no significant effect on LVM (314 +/- 29 versus 286 +/- 32 g). The decrease in LVM observed with perindopril was associated with a reduction in LVEDD (49.9 +/- 1.6 versus 54.3 +/- 1.4 mm after 12 months) (time-treatment interaction, P = .04), while the mean LV wall thickness was unchanged (11.4 +/- 0.3 versus 10.5 +/- 0.5 mm). Cardiac alterations were not correlated with changes in BP or with alterations in plasma renin activity or aldosterone or catecholamine levels.

CONCLUSIONS

In ESRD patients with LVH, ACE inhibition decreases LVM independently of its antihypertensive effect and of associated alterations in arterial hemodynamics. The decrease in LVM was due primarily to a decrease in LV volume, which may have resulted in these patients from chronic volume overload.

Tolerability of enalapril initiation by patients with left ventricular dysfunction: results of the medication challenge phase of the Studies of Left Ventricular Dysfunction

Although converting-enzyme inhibitors are useful for the treatment of congestive heart failure (CHF), there are concerns about adverse reactions especially on initiation of therapy. In the Studies of Left Ventricular Dysfunction, enalapril, 2.5 mg twice per day was given on an open-label outpatient basis for 7 days (mean 6.1, range 2 to 7, and median 7) as a prerandomization drug challenge to 7487 patients with left ventricular dysfunction (ejection fraction < or = 0.35). Four hundred forty-four (5.93%) patients reported side effects, including symptoms attributed to hypotension (in 166 patients [2.2%]). The majority (346 [77.9%] of 444 and 129 [77.7%] of 166 with symptoms attributed to hypotension) of patients who reported side effects were willing to participate in the study and to continue receiving enalapril. Thus only 98 (1.3%) of 7487 patients (0.5% because of symptoms attributed to hypotension) were not willing to continue because of side effects. Women and patients of CHF class III or IV were more likely to report side effects. In conclusion, enalapril is well tolerated by patients with left ventricular dysfunction; treatment can be initiated on an outpatient basis in the majority of patients.

Lack of correlation between the acute haemodynamic response to intravenous captopril and plasma concentrations of angiotensin II in patients with chronic cardiac failure

We have given a series of incremental intravenous injections of captopril to ten patients with chronic cardiac failure. Small doses of captopril produced significant changes in pulmonary artery end-diastolic pressure and right atrial pressure, up to a total cumulative dose of captopril of 2.5 mg, after which further injections had no significant effect. There were large changes in systemic vascular resistance and blood pressure up to a cumulative dose of captopril of 5.0 mg, after which the injection of larger doses caused no further significant changes. Small doses of intravenous captopril produced large increases in plasma renin activity and plasma angiotensin I concentrations up to a total cumulative dose of captopril of 1.25 mg, after which there were no significant further changes in either plasma renin activity or plasma angiotensin I concentration. However the plasma concentration of angiotensin II fell more slowly, no further change being recorded after a total cumulative dose of captopril of 10 mg. These results suggest that plasma renin activity is not the only determinant of plasma angiotensin II concentrations.

Short-term vasodilator effect of captopril in patients with severe mitral regurgitation is parasympathetically mediated

BACKGROUND

Few data exist regarding the effects of angiotensin converting enzyme inhibitors in patients with regurgitant valvular lesions. We postulated an immediate improvement in cardiac performance with captopril in mitral regurgitation, which, in a hemodynamically compensated group of patients, might be mediated through parasympathetic vasodilation rather than through blockade of angiotension converting enzyme.

METHODS AND RESULTS

Hemodynamics were examined before and 90 minutes after oral captopril (25-50 mg) in 18 patients (mean age, 31 years) with chronic, severe mitral regurgitation in New York Heart Association functional class II and III. One group of patients was given captopril alone (group 1, n = 9) and a second group was given captopril plus atropine 0.04 mg/kg i.v. (group 2, n = 9). Captopril alone (group 1) produced decreases in heart rate (90-81 beats/min, p less than 0.001), mean arterial pressure (90-73 mm Hg, p less than 0.001), systemic resistance (28-23 Wood units, p = 0.068), and pulmonary wedge pressure (19-14 mm Hg, p less than 0.001). There was no improvement in either arteriovenous oxygen difference or thermodilution cardiac output; in fact, the latter slightly declined (3.45-3.35 l/min, p = 0.002). Pretreatment with atropine (group 2) diminished the effects of captopril on heart rate (107-103 beats/min, p = 0.065 for atropine effect by two-way ANOVA), mean arterial pressure (88-82 mm Hg, p = 0.01 for atropine effect), and systemic resistance (26-27 Wood units, p = 0.04 for atropine effect).

CONCLUSIONS

In patients with chronic, severe mitral regurgitation, captopril reduced systemic arterial and left ventricular filling pressures but did not immediately augment cardiac output as expected. Furthermore, the modest systemic vasodilator effect of captopril was parasympathetically mediated.

Modulation of venous tone in heart failure

Venodilatation may be an important property in drugs used to treat heart failure. Deductions about venous tone from standard hemodynamic studies may be misleading since filling pressures may be reduced by improved left ventricular function. To study the venodilator properties of drugs, we have modified a radionuclide blood pool method and shown that venous volume is increased by 10% after glyceryl trinitrate but is unchanged after the arteriolar dilator hydralazine. In patients with congestive cardiac failure, the calcium channel blocker, felodipine, causes a marked reduction in systemic vascular resistance and left ventricular filling pressures, but venous volume remains unchanged. In a similar group of patients comparable arterial and central effects are seen after the administration of captopril, but venous volume increases by 16%, and this increased venous volume is sustained after 3 months of long-term treatment. Milrinone has been used to treat both acute and chronic heart failure. As expected of a phosphodiesterase inhibitor, it exhibits inotropic properties in animals and humans and also causes arterial vasodilatation. We have studied its effects on venous tone in 10 patients with severe heart failure (New York Heart Association classes III to IV). Milrinone was given intravenously at a loading dose of 50 micrograms/kg followed by an infusion of 0.5 micrograms/kg/min. After treatment, cardiac index, which was measured by thermodilution, increased from 1.8 +/- 0.48 to 2.3 +/- 0.65 L/min/m2 (p less than 0.001); pulmonary artery wedge pressure fell from 23 +/- 6 to 11 +/- 5 mm Hg (p less than 0.001); and systemic vascular resistance index decreased from 4296 to 3168 dynes.sec.cm-5/m2 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of ace inhibition on peripheral hemodynamics in normotensive and hypertensive patients with type II diabetes

The effect of treatment with enalapril (10 days at 10 mg/d followed by 4 weeks at 20 mg/d) on forearm hemodynamics was assessed in eight normotensive patients and eight patients with hypertension affected by Type II diabetes as well as in eight patients with essential hypertension and normal glucose tolerance. The ACE inhibitor decreased regional vascular resistances and increased the maximum arteriolar-vasodilating capacity and venous distensibility in the three groups of patients. Thus, this study shows that ACE inhibition by enalapril improves regional hemodynamics in patients with Type II diabetes.

Hemodynamic and cardiac effects of spiraprilat in normal and sodium depleted conscious dogs

The cardiac and hemodynamic effects of 3 doses (0.1, 0.3 and 1 mg/kg, iv) of spiraprilat, the diacid active metabolite of the new angiotensin I converting enzyme inhibitor spirapril, have been investigated and compared to those of saline in chronically implanted conscious dogs at rest. Under a normal sodium diet, spiraprilat, 1 mg/kg, induced significant (at least P less than 0.05) decreases in mean arterial pressure (MAP, -11%), total peripheral resistance (TPR, -21%), left ventricular end diastolic pressure (LVEDP, -15%) and increases in heart rate (HR, +12%) and cardiac output (CO, +16%) whereas dP/dtmax remained unchanged. Spiraprilat-induced tachycardia was not modified by propranolol pre-treatment but was abolished by previous administration of the propranolol-N-methylatropine combination. Spiraprilat, 0.1 mg/kg, did not affect any parameter, but spiraprilat, 0.3 mg/kg, showed intermediate effects. Finally, sodium depletion strongly potentiated spiraprilat effects on MAP, TPR, LVEDP, HR and CO. We conclude that: a), in conscious dogs under normal sodium diet, spiraprilat reduces TPR and MAP through peripheral vasodilating properties; b), spiraprilat-induced tachycardia is mainly related to parasympathetic tone withdrawal, possibly in relation with high and low pressure baroreceptors deactivation; and c), sodium depletion considerably potentiates spiraprilat cardiac and hemodynamic effects.

Effects of captopril versus milrinone therapy in modulating the adrenergic nervous system response to exercise in congestive heart failure

The potential adverse consequences of increased adrenergic nervous system activity in patients with heart failure are now recognized. Modulation of the plasma noradrenaline response to submaximal exercise should be desirable. The long-term (9 weeks) effects of milrinone (10 mg 4 times a day) or captopril (50 mg 3 times a day) compared to placebo were evaluated in a double-blind crossover study, in 16 patients with stable, congestive heart failure receiving digoxin and furosemide. After treatment, clinical status (score range 0 to 14 points) improved significantly with both milrinone (4.4 +/- 0.5, p less than 0.01) and captopril (4.1 +/- 0.4, p less than 0.01). Plasma noradrenaline at rest was similar with both drugs and not significantly different from placebo. During submaximal exercise it increased significantly to 1,228 +/- 58 pg/ml with placebo and to 1,295 +/- 174 pg/ml with milrinone; this response was reduced significantly with captopril, to 820 +/- 100 pg/ml (p less than 0.01). Thus, long-term therapy with both captopril and milrinone improved the clinical score, but only captopril reduced the plasma noradrenaline response to submaximal exercise. These findings suggest that angiotensin-enzyme inhibition with captopril will modulate the adrenergic system response to daily activities in patients with chronic congestive heart failure and therefore could have additional salutary effects beyond vasodilatation.

Captopril in children with dilated cardiomyopathy: acute and long-term effects in a prospective study of hemodynamic and hormonal effects

Hemodynamic and hormonal effects of captopril were prospectively studied in 12 children (median age 5.8 years, range 4 weeks to 15 years) with dilated cardiomyopathy. A mean dose of 1.83 mg captopril/kg body weight was administered in three or four single doses depending on age. Left ventricular volume, ejection fraction (EF), cardiac index (CI), and systemic vascular resistance (SVR) were noninvasively determined by two-dimensional (2D) and Doppler echocardiography before and 2 days and 3 months after the onset of treatment. Blood pressure and heart rate were recorded as well. Additionally, on the day hemodynamic measurements were made, plasma renin activity (PRA), serum aldosterone, and plasma atrial natriuretic peptide (ANP) concentrations were determined. Plasma catecholamines were measured before and 2 days after captopril treatment. Concomitant medication was kept constant during the short-term phase of captopril treatment. During long-term therapy, diuretics were reduced according to the clinical status. Stroke volume (SVI) (-7%), end-systolic (ESVI) (-31%), and end-diastolic (EDVI) (-21%) volume indexes were significantly reduced (p less than 0.05) during short- and long-term therapy. The remaining hemodynamic parameters showed only minor, statistically not significant, changes. During short-term therapy, median serum aldosterone levels fell from 138-88.5 pg/ml (p less than 0.05), and plasma ANP decreased from 144-94 pg/ml (p less than 0.05). After 3 months these effects were less marked and statistically no longer significant. Changes in PRA and plasma catecholamines were not statistically significant at any time.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute and chronic arterial and venous effects of captopril in congestive cardiac failure

OBJECTIVE

To determine whether captopril alters peripheral venous tone in patients with congestive cardiac failure.

DESIGN

Open study of patients at start of captopril treatment and three months later.

SETTING

A hospital gamma camera laboratory.

PATIENTS

16 Men with congestive cardiac failure in New York Heart Association class II or III, aged 57-73.

INTERVENTIONS

Patients were initially given 500 micrograms sublingual glyceryl trinitrate followed by 25 mg oral captopril. The study was then repeated after three months' captopril treatment.

MAIN OUTCOME MEASURES

Previously validated non-invasive radionuclide techniques were used to measure changes in central haemodynamic variables and peripheral venous volumes in the calf.

RESULTS

After 25 mg captopril there were falls in blood pressure and relative systemic vascular resistance and increases in cardiac index and left ventricular ejection fraction. This was accompanied by a 16% increase in peripheral venous volume (95% confidence interval 13.4% to 18.4%, p less than 0.01), which compared with an 11% increase after 500 micrograms glyceryl trinitrate (10% to 12%, p less than 0.01). Eleven patients were restudied after three months' continuous treatment with captopril. The resting venous volume was higher than it had been initially, by about 10%, and increased by a further 8.4% after 25 mg captopril (5.4% to 11.4%, p less than 0.05).

CONCLUSIONS

Captopril is an important venodilator. Venous and arterial dilatation are produced short term and during long term treatment.

Comparison of the immediate and long-term effects of captopril and isosorbide dinitrate as adjunctive treatment in mild heart failure

1. The efficacy of captopril and isosorbide dinitrate (ISDN) as adjunctive therapy to digoxin and diuretics in mild heart failure was compared in a double-blind study. 2. Twenty-one patients were randomly allocated to captopril (twice or three times daily) or ISDN. Eighteen patients completed a protocol of placebo run-in, dose titration and maintenance treatment for 3 months. 3. Symptom-limited exercise tolerance, ejection fraction and radionuclide indices of diastolic function estimated by gated blood pool scan did not change with either treatment. 4. Captopril improved functional class (Canadian Cardiovascular Society) and reduced requirements for increased diuretic dosage at both 1 and 3 months of maintenance treatment. Patients treated with ISDN required increased diuretic and did not improve their functional class. Differences between the treatments were significant only for diuretic dosage requirements. 5. We conclude that adjunctive therapy of mild heart failure with captopril administered twice daily provides a diuretic-sparing effect and may improve functional class during 3 months of maintenance treatment.

[Effect of captopril therapy on sodium and water excretion in patients with liver cirrhosis and ascites]

Ascites in patients with cirrhosis of the liver frequently is refractory to diuretic treatment. It was postulated that vasoconstriction of the renal cortex, mediated by activation of the renin-angiotensin-aldosterone-system (RAAS), may be one course of the disturbed sodium- and water-excretion in these patients. We therefore investigated in 14 cirrhotic patients with ascites under constant diuretic treatment the effects of low-dose captopril therapy on urinary sodium- and potassium-excretion, body weight, abdominal girth, serum-sodium, -potassium, creatinine-clearance, plasma-renin-activity (PRA), plasma-aldosterone (PA) and mean arterial pressure (MAP). After a control period of 4 days the patients received 2 x 6.25 mg/d captopril for 5 days and 4 x 6.25 mg/d for further 5 days. Treatment was followed by a second control period without captopril. PRA increased significantly after 2 days of captopril treatment. 2 x 6.25 mg/d captopril induced a significant increase in sodium excretion and a significant decrease of body weight. MAP decreased slightly but significantly without clinical signs of hypotension. 4 x 6.25 mg/d captopril resulted in a further reduction of body weight and a further enhancement of sodium excretion. Three days after withdrawal of captopril sodium output was significantly reduced again.

CONCLUSION

In cirrhotic patients low-dose captopril seems to be efficient in the treatment of ascites resistant to diuretics without causing major side effects.

Angiotensin-converting enzyme inhibitors in heart failure

Recognition of the importance of the renin-angiotension-aldosterone system in heart failure, along with an appreciation of the hemodynamic benefits of vasodilator therapy has led to the widespread use of angiotensin-converting enzyme (ACE) inhibitors in the treatment of heart failure. The ACE inhibitors are the only class of vasodilator agents shown to have a significant protective effect against mortality in patients with heart failure.

Importance of venodilatation in prevention of left ventricular dilatation after chronic large myocardial infarction in rats: a comparison of captopril and hydralazine

In rats with large myocardial infarctions, we compared the effects of captopril, a presumed arterial and venous vasodilator, with hydralazine, which is thought primarily to be an arterial vasodilator. To determine if the effects of captopril were dependent on the pathophysiological consequences of heart failure, we also studied a group of noninfarcted rats treated with captopril. In noninfarcted rats treated with captopril, left ventricular (LV) systolic and mean aortic pressures decreased from 132 +/- 12 to 107 +/- 15 mm Hg and 122 +/- 1 to 100 +/- 2, respectively (p less than 0.01). In noninfarcted rats, captopril decreased LV weight, LV weight/body weight, and total heart weight/body weight but produced no effects on the peripheral venous circulation. Rats subjected to coronary artery ligation were selected by ECG criteria to have large myocardial infarctions and were treated for 4 weeks with captopril (n = 8), hydralazine (n = 5), or placebo (n = 9). In infarcted rats treated with captopril, LV systolic, mean aortic pressures and LV end-diastolic pressure (LVEDP) decreased (p less than 0.01) from 115 +/- 4 to 86 +/- 3 mm Hg, 106 +/- 4 to 74 +/- 3 mm Hg, and 23 +/- 2 to 11 +/- 2 mm Hg, respectively. Mean circulatory filling pressure decreased (p less than 0.05) from 11.2 +/- 0.6 to 8.7 +/- 0.8 mm Hg and venous compliance increased (p less than 0.05) from 2.04 +/- 0.07 to 2.70 +/- 0.20 ml/mm Hg/kg. Blood volume decreased (p less than 0.05) from 67.3 +/- 0.9 to 58.2 +/- 1.8 ml/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme inhibitors. II. Clinical use

Since their introduction in clinical practice in 1980, ACE inhibitors have been found useful in the treatment of hypertension and CHF. In hypertension, they are effective as monotherapy in 40% to 50% of the patients, and in combination with diuretics or calcium antagonists, they are effective in up to 85% of the patients. They are well tolerated, are not associated with depression, impotence, bronchospasm or metabolic derangements such as hypokalemia, hyperuricemia or hyperglycemia, and do not have adverse effects on the quality of life. As a result, they are preferred in hypertensive patients with CHF, left ventricular dysfunction, mental depression, older age, coronary artery disease, metabolic disorders, chronic destructive pulmonary disease, and peripheral vascular disease. In CHF they cause long-lasting hemodynamic and symptomatic improvement, improve exercise tolerance, and may lower mortality in certain patient subsets. Evolving new indications for ACE inhibitors include the diagnosis of renovascular hypertension, the prediction of surgical success, the treatment of scleroderma renal crisis, the reduction of proteinuria, renal protection, cardioprotection, the improvement of arterial compliance, in Bartter's syndrome and idiopathic edema, etc. ACE inhibitors are usually well tolerated but in some instances they may cause class-specific side effects such as hypotension; usually reversible azotemia or renal failure, especially in patients with renal artery stenosis or with CHF with low blood pressure; cough; angioedema; and hyperkalemia. Differences among ACE inhibitors are emerging and include chemical class (e.g., zinc ligand), biotransformation, potency, pharmacokinetics, prodrugs, tissue effects, additional pharmacologic properties, and drug interactions.

Synergistic effect of captopril and dobutamine on left ventricular pressure-volume and pressure-shortening relations in severe cardiac failure

The acute effects of captopril and dobutamine, alone and in combination, on left ventricular contractility were assessed from left ventricular end-systolic pressure-volume and pressure-shortening relations in 6 patients with severe end-stage cardiac failure. Dobutamine was given by constant intravenous infusion on two occasions 48 hours apart, on one of these occasions the patient also received oral captopril in a dose of 37 +/- 12 mg 6-hourly. Pressures and cardiac index were measured, and left ventricular volumes and ejection fraction computed from simultaneously recorded radionuclide ventriculography. Dobutamine alone did not cause a statistically significant increase in stroke index, stroke work index, cardiac index and ejection fraction, although pulmonary capillary wedge pressure and right atrial pressure fell (P less than 0.05). There was no change in systemic or pulmonary vascular resistance nor in arterial blood pressure. Following administration of captopril, diastolic arterial pressure decreased (P less than 0.05), and the dobutamine challenge produced a greater and significant rise in stroke and stroke work index (P less than 0.05) and cardiac index (P less than 0.01). The left ventricular contractile state was unaltered by captopril but appeared to increase with dobutamine and more so during combined therapy with captopril and dobutamine, indicating a synergistic effect of the two drugs when given in combination.

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.

Effect of captopril on left ventricular end-systolic pressure-volume and stress-shortening relations in severe cardiac failure

The effects of captopril on cardiovascular dynamics and left ventricular (LV) contractility were studied in 11 patients with severe congestive heart failure and very poor global LV function. Pressures were measured using a flow-guided catheter, cardiac output by thermodilution, and LV contraction and ejection fraction by simultaneous radionuclide angiography. Ventricular loading conditions were altered by sublingual isosorbide dinitrate to facilitate construction of LV pressure-volume and stress-shortening curves. Captopril decreased mean arterial pressure (p less than 0.02) and systemic vascular resistance, while stroke and cardiac index increased in most patients. Left ventricular ejection fraction increased from 18 +/- 5 to 22 +/- 7% (p less than 0.05), but contractility, assessed from end-systolic pressure-volume and end-systolic pressure-shortening relations, was unchanged or decreased slightly. Heart rate and double product also tended to decrease. In contrast, arteriovenous oxygen difference widened and calculated total oxygen consumption increased during captopril therapy (p less than 0.05). The study showed that captopril improved forward blood flow, total oxygen extraction, and LV ejection fraction following the decrease impedance to LV emptying but not at the expense of an increase in ventricular contractility. This makes captopril an attractive drug for patients with end-stage cardiac failure and a severely damaged myocardium.

Effects of four angiotensin I converting enzyme inhibitors on regional myocardial blood flow and ischemic injury during coronary artery occlusion in dogs

The effects of 4 angiotensin I converting enzyme inhibitors (ACEI), captopril, enalapril, ramipril, and trandolapril, were investigated on regional myocardial blood flow (RMBF, radioactive microspheres) distribution in ischemic and nonischemic zones and on ST-segment elevation in ischemic zones during intermittent coronary artery occlusion in anesthetized dogs. The 4 ACEI inhibited plasma ACE activity to an almost similar extent. All similarly reduced systemic blood pressure, an effect related to a decrease in systemic vascular resistance. Heart rate and myocardial contractility were not affected, but myocardial oxygen consumption presumably decreased because of the reduction in afterload. RMBF and their distribution (between epicardial and endocardial layers and between nonischemic and ischemic zones) were not modified by ACEI. Coronary vascular resistance was slightly decreased in nonischemic zones. ACEI had no effect on ST-segment elevation in ischemic zones. Thus, in this experimental model, all ACEI exhibited the same profile, including no change in RMBF and affording no protection against ischemic injury.

Angiotensin II, aldosterone and arginine vasopressin in plasma in congestive heart failure

Angiotensin II (AII), aldosterone (Aldo) and arginine vasopressin (AVP) in plasma were determined during basal conditions in seventeen patients with congestive heart failure and in seventeen control subjects. The same parameters were measured before and 1, 2 and 3 h after an oral water load of 20 ml (kg body weight)-1 together with urine volume (V) and free water clearance (CH2O) in seven patients with congestive heart failure and in seven control subjects. AII, Aldo and AVP were significantly higher in heart failure than in control subjects (AII:81 and 12 pmol l(-1) (medians), P less than 0.01; Aldo: 411 and 103 pmol l(-1), P less than 0.01; AVP: 5.3 and 2.0 pmol l)-1), P less than 0.01). AVP was positively correlated to Aldo in both heart failure (p = 0.593, n = 17, P less than 0.02) and control subjects (p = 0.511, n = 17, P less than 0.05), but in neither of the groups to AII. V and CH2O were significantly lower in heart failure when compared to control subjects (maximum increase in CH2O 3.55 and 5.86 ml min-1, P less than 0.02), but did not correlate directly with either A II, Aldo or AVP. Creatinine clearance was reduced in heart failure. It is concluded that the activity of both the renin-angiotensin-aldosterone system and the osmoregulatory system is enhanced in congestive heart failure, presumably as a compensatory phenomenon in order to maintain arterial blood pressure. It is suggested that the decrease in free water clearance may be attributed to both an elevated level of vasopressin and a reduced glomerular filtration rate.

Mixed venous blood temperature response to exercise in heart failure patients treated with short-term vasodilators

Deep-body or core temperature decreases during exercise in patients with heart failure, primarily due to the circulatory inadequacies associated with the pathophysiology of this condition. Vasodilators are commonly used to treat patients suffering from heart failure because these drugs improve total cardiac output and blood-flow to the regional circulations. In heart failure patients, the core temperature response to exercise should also be affected if the circulation is improved by vasodilators. Patients with severe heart failure were studied at rest and during upright bicycle exercise before, and after, short-term treatment with vasodilators (2-minoxidil, 3-hydralazine, 5-captopril). Their heart rate increased significantly (P less than 0.05) from rest to exercise before (87 +/- 15 109 +/- 14 beats/min), and after 89 +/- 13- 112 +/- 15 beats/min) vasodilators, but there was no drug-related affect on these changes. Mean arterial and pulmonary capillary wedge pressures were significantly (P less than 0.05) decreased at rest and after the administration of vasodilators (mean arterial pressure 88 +/- 7 mmHg before; 77 +/- 8 mmHg after; pulmonary capillary wedge pressure 25 +/- 8 mmHg before, 19 +/- 9 mmHg after). During exercise, the increases in mean arterial and pulmonary capillary wedge pressures were not significantly different from the before vasodilator values (mean arterial pressure 92 +/- 14 mmHg before, 87 +/- 14 mmHg after; pulmonary capillary wedge pressure 31 +/- 11 mmHg before, 29 +/- 11 mmHg after). Vasodilators increased cardiac output significantly (P less than 0.05) at rest (3.1 +/- 0.6 litre/min to 4.1 +/- 1.1 litre/m) and during exercise (4.8 +/- .2 litre/min-5.6 +/- 1.7 litre/min). The core temperature (mixed venous blood temperature) decreased significantly (P less than 0.05) during exercise from 37.04 +/- 0.62 degrees C to 36.65 +/- 0.65 degrees C, before treatment with vasodilators. After administration of vasodilators, resting core temperature was not significantly different (36.95 +/- 0.54 degrees C) and still decreased significantly (P less than 0.05) during exercise to 36.73 +/- 0.53 degrees C. This decrease was significantly (P less than 0.05) different from the core temperature response before the administration of vasodilators. We conclude that heart failure patients, treated with short-term vasodilators, have an attenuation of the core temperature response that typically occurs during exercise. This change in the core temperature response is the result of the vasodilator-induced improvement in circulation.

Controlled trial of enalapril in congestive cardiac failure

Twenty five patients with chronic congestive cardiac failure had enalapril (n = 13) or placebo (n = 12) added to their existing regimen of digoxin and frusemide in a randomised double blind trial. Four hours after the first 5 mg dose, the enalapril group showed significant falls in blood pressure, heart rate, and concentrations of plasma angiotensin II, angiotensin converting enzyme, and noradrenaline. During the 12 week trial heart failure became worse in one enalapril treated patient (8%) and in seven placebo treated patients (58%). There were no significant changes in cardiac ejection fraction or exercise duration in either group. Plasma noradrenaline response to graded exercise and maximum exercise rate-pressure product were significantly reduced after four and 12 weeks of active treatment but unchanged with placebo treatment. There was a sustained increase in plasma potassium and a slight rise in plasma creatinine in the enalapril group. Plasma concentrations of the active drug, enalaprilate, were dose related and log enalaprilate correlated significantly with percentage of plasma angiotensin converting enzyme activity (r = -0.66). Enalapril was well tolerated and produced no adverse effects. The drug appears to be superior to placebo and offers considerable promise for the treatment of this condition.

Effect of the renin-angiotensin system on limb circulation and metabolism during exercise in patients with heart failure

The maximal aerobic exercise capacity of patients with chronic heart failure is frequently decreased because of inadequate blood flow to working skeletal muscle. To investigate whether this reduced flow is in part due to interference by angiotensin II with arteriolar dilation in working muscle, the effect of the angiotensin-converting enzyme inhibitor captopril on leg blood flow, leg vascular resistance, leg oxygen consumption (VO2) and leg lactate release during maximal upright bicycle exercise was examined in 12 patients with heart failure (maximal VO2 10.7 +/- 3.1 ml/min per kg). Captopril decreased leg resistance at rest (258 +/- 115 to 173 +/- 67 U, p less than 0.01) and maximal exercise (68 +/- 69 to 45 +/- 29 U, p less than 0.01) associated with proportionately similar decreases in systemic vascular resistance. However, maximal exercise duration and maximal VO2 were unchanged and, at identical peak exercise work times, there was no improvement in leg blood flow (2.0 +/- 0.9 to 2.0 +/- 1.1 liters/min, p = NS), leg VO2 (261 +/- 104 to 281 +/- 157 ml/min, p = NS) or leg lactate release (269 +/- 149 to 227 +/- 151 mg/min, p = NS). These data suggest that, during exercise in patients with heart failure, angiotensin II does not interfere with blood flow to working skeletal muscle.

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)

Influence of chronic captopril therapy on the infarcted left ventricle of the rat

To determine whether the relationship between infarct size and ventricular performance, volume, and compliance could be altered favorably, captopril was administered to rats for 3 months following coronary artery ligation. Baseline left and right ventricular and systemic arterial pressures and aortic blood flow, and maximal stroke volume and cardiac indices attained during a volume loading, were measured. Passive pressure-volume relations of the left ventricle were determined, and the slopes of segments of this relation were analyzed to characterize ventricular chamber stiffness. In untreated rats, left ventricular end-diastolic pressure progressively rose (from 5-28 mm Hg) as a function of infarct size, whereas, in captopril-treated rats, filling pressure remained within normal limits (5 +/- 1 mm Hg) in all but those with extensive infarcts. Chronic captopril therapy reduced baseline mean arterial pressure and total peripheral resistance, yet maintained cardiac and stroke outputs in rats both with and without infarcts. In untreated rats, maximal pumping ability progressively declined with increasing infarct size, whereas, in captopril-treated rats, peak stroke volume index remained within normal limits in all but those with extensive infarcts. The in vitro left ventricular volumes of captopril-treated rats were significantly less than those of untreated rats. The maintenance of forward output from a lesser dilated left ventricle yielded an index of ejection fraction for treated rats with moderate and large infarcts that was significantly elevated compared with that of untreated rats with infarcts of comparable size. Left ventricular chamber stiffness, which fell as infarct size increased in untreated rats, was normalized by chronic captopril therapy. Thus, captopril attenuated the left ventricular remodeling (dilation) and deterioration in performance that were observed in rats with chronic myocardial infarction.

Supine and sitting maximal workload difference and response to long-term enalapril therapy in congestive heart failure

Maximal workloads in supine and sitting bicycle stress tests were compared in 12 patients with congestive heart failure during long-term therapy with the vasodilator enalapril. The response to the therapy was observed with the supine and sitting bicycle stress tests and gated equilibrium ventriculography. The maximal workload was 68 W in the supine position and 84 W in the sitting position; the mean difference was 15 W. The difference was highly significant (P less than 0.001). Both the supine and sitting workloads were significantly higher (P less than 0.02 and P less than 0.05) in the enalapril group than in the placebo group. The findings in the gated equilibrium ventriculography were not significantly different between the two groups.

Influence of chronic renal failure on captopril pharmacokinetics and clinical and biological effects in hypertensive patients

The pharmacokinetic parameters of unchanged plasma captopril and the kinetics of the drug effects on plasma converting enzyme activity (PCEA), plasma renin activity (PRA), plasma aldosterone (PA) and mean blood pressure (MBP) were studied over 24 h after oral administration in three groups of hypertensive patients: with normal renal function (group 1, plasma creatinine less than 110 mumol/l, n = 10), with moderate chronic renal failure (group 2, 135 less than plasma creatinine less than 450 mumol/l, n = 10) and with severe chronic renal failure (group 3, plasma creatinine greater than 500 mumol/l, n = 10). Renal impairment had no effect on plasma captopril Cmax, CLtot and relative bioavailability (AUC). In contrast, captopril kel decreased while T1/2 increased progressively from group 1 to group 3. PCEA blockade (T1/2 and AUC) was increased significantly and proportionally to the degree of renal impairment. However, there were no differences between the three groups regarding captopril-induced modifications of PRA and PA. Although the maximal reduction in MBP was identical in the three groups, the overall antihypertensive effect (AUC) of captopril increased significantly and progressively from group 1 to group 3, especially in duration. There was no correlation between basal plasma creatinine values and unchanged captopril relative bioavailability (AUC) and between unchanged captopril relative bioavailability (AUC) and the drug effects (AUC) on PCEA, PRA, PA and MBP. However there was a correlation between basal plasma creatinine values and plasma captopril T1/2, PCEA blockade (AUC) and overall antihypertensive effect (AUC). The apparent discrepancy between the lack of effects of chronic renal failure on plasma unchanged captopril bioavailability and its potentiating effects on PCEA blockade and MBP reduction may be accounted for by the renal impairment-induced accumulation of captopril metabolites.

Acute and chronic hemodynamic effects of enalapril (MK-421) in congestive heart failure

Enalapril, a new long-acting angiotensin-converting enzyme inhibitor, was administered orally to 12 patients with stable congestive cardiac failure, NYHA function class III-IV. Acute and chronic hemodynamic effects were evaluated in addition to clinical response. The results of this open pilot study indicated marked reduction of pulmonary capillary wedge pressure from 21.8 +/- 5.9 mm Hg (mean +/- 1 SD) to 13.3 +/- 4.5 mm Hg (P less than 0.01) and peripheral resistance from 1837 +/- 860 dynes X sec-1 X cm-5 to 1063 +/- 584 dynes X sec-1 X cm-5 at 6 hr (P less than 0.01). Well-tolerated hypotension with mean arterial pressure from 88.0 +/- 11.6 mm Hg to 73.1 +/- 11.7 mm Hg at 6 hr (P less than 0.01) was recorded. No significant increase in cardiac output was observed. Angiotensin-converting enzyme activity was powerfully inhibited at the time of peak hemodynamic effect from 25.3 +/- 9.8 U/ml to 4.9 +/- 3.4 U/ml (P less than 0.01) and sustained, but attenuated reduction at 24 hr (8.7 +/- 4.7 U/ml) was observed. All patients reported subjective improvement and this clinical improvement has been sustained during follow-up from 19 to 21 months although baseline hemodynamic parameters at chronic re-catheterization did not demonstrate significant improvement. The pharmacodynamics and toxicity of enalapril as compared to captopril are discussed. The long half-life, low toxicity and gradual onset of action are seen as representing a clinical advantage with regard to patient therapy.

Efficacy of captopril in low-renin congestive heart failure: importance of sustained reactive hyperreninemia in distinguishing responders from nonresponders

To determine the efficacy of converting-enzyme inhibition in patients with low-renin congestive heart failure (CHF), the long-term hemodynamic and clinical responses to captopril were evaluated in 26 consecutive patients with severe, chronic CHF whose pretreatment plasma renin activity (PRA) was less than 2 ng/ml/hour. After 2 to 8 weeks of continuous treatment with captopril, 14 patients (54%) showed long-term hemodynamic benefits, of whom 13 (50%) improved clinically by at least 1 New York Heart Association functional class. To distinguish responders from nonresponders, patients were grouped based on the presence or absence of sustained reactive hyperreninemia (PRA during chronic therapy greater than 4 ng/ml/hour). After 2 to 8 weeks of therapy with captopril, 14 patients had sustained reactive hyperreninemia. Their cardiac index increased by 0.33 liters/min/m2 (p less than 0.01), left ventricular filling pressure decreased by 12.6 mm Hg (p less than 0.001), mean right atrial pressure decreased by 4.9 mm Hg (p less than 0.001) and systemic vascular resistance decreased by 529 dyne s cm-5 (p less than 0.001). Twelve of these 14 patients improved clinically. Twelve other patients had no reactive increase in PRA, and these patients showed no significant improvement in any hemodynamic variable after 2 to 8 weeks of treatment with captopril; only 1 of the 12 patients improved clinically (p less than 0.001 between groups). The 2 groups were otherwise similar with regard to pretreatment demographic, hemodynamic and hormonal variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Dilation of forearm blood vessels after angiotensin-converting-enzyme inhibition by captopril in hypertensive patients

In eight hypertensive patients, forearm vascular tone was assessed by water plethysmography following inhibition of angiotensin II-converting-enzyme (ACE) activity with captopril. Acute captopril administration increased venous distensibility (VV30) and decreased forearm vascular resistance (FVR), while it lowered systemic blood pressure (BP). Alpha-one adrenergic receptor blockade by prazosin did not prevent captopril from decreasing vascular tone or lowering blood pressure (BP). Thus, captopril dilated both veins and arterioles. The primary mechanism of captopril's acute antihypertensive action did not involve inhibition of alpha1-adrenergic receptor activity. Moreover, captopril and prazosin together produced a greater reduction in BP and peripheral resistance than occurred with either agent alone.

Estimation of angiotensin II receptor activity in chronic congestive heart failure

The renin-angiotensin system has been shown to participate in the pathophysiology of chronic heart failure in many patients. However, the immediate assessment of this contribution in individual patients may sometimes be difficult. As a pharmacologic estimate of angiotensin II receptor activity, we infused the angiotensin II analogue, saralasin, in 20 patients with severe chronic congestive heart failure (CHF). The infusion resulted in blood pressure responses ranging from an agonist pressor response (increased systemic resistance) in patients with low intrinsic renin-angiotensin system activity, to an antagonist depressor response (decreased systemic resistance) in patients with marked activation of the renin-angiotensin system. The ability of the saralasin response to pharmacologically estimate angiotensin II receptor activity in CHF was further revealed by two physiologic maneuvers that decrease endogenous circulating angiotensin II and angiotensin II receptor occupancy. Both converting enzyme inhibition with captopril and sodium repletion, factors known to decrease endogenous angiotensin II activity, provoked agonist responses to saralasin infusion. Furthermore, saralasin was able to reverse the orthostatic hypotension precipitated by converting enzyme inhibition of angiotensin-dependent vascular tone. In summary, saralasin provided a means to estimate angiotensin receptor activity and may therefore serve as a probe of angiotensin-mediated vasoconstriction in the pathophysiology of chronic CHF.