Captopril in clinical hypertension. Changes in components of renin-angiotensin system and in body composition in relation to fall in blood pressure with a note on measurement of angiotensin II during converting enzyme inhibition

The first bioactive (angiotensin-converting enzyme-inhibitory) peptide isolated from pearl matrix protein

In this research, we unveil the medical potential of pearls by identifying a novel bioactive peptide within them for the first time. The peptide, termed KKCHFWPFPW, emerges as a pioneering angiotensin I-converting enzyme (ACE) inhibitor, originating from the pearl matrix of Pinctada fucata. Employing quadrupole time-of-flight mass spectrometry, this peptide was meticulously selected and pinpointed. With a molecular weight of 1417.5 Da and a theoretical isoelectric point of 9.31, its inhibitory potency was demonstrated through a half-maximal inhibitory concentration (IC50) of 4.17 μM, established via high-performance liquid chromatography. The inhibition of ACE by this peptide was found to be competitive, as revealed by Lineweaver-Burk plot analysis, where an increase in peptide concentration correlated with an enhanced rate of ACE inhibition. To delve into the interaction between KKCHFWPFPW and ACE, molecular docking simulations were conducted using the Maestro 2022-1 Glide software, shedding light on the inhibitory mechanism. This investigation suggests that peptides derived from the P. martensii pearl matrix hold promise as a novel source for antihypertensive agents.

Gaussian Accelerated Molecular Dynamics Simulations Investigation on the Mechanism of Angiotensin-Converting Enzyme (ACE) C-Domain Inhibition by Dipeptides

Angiotensin-converting enzyme (ACE)-inhibitory peptides extracted from food proteins can lower blood pressure by inhibiting ACE activity. A recent study showed that the inhibitory activity of IY (Ile-Tyr, a dipeptide derived from soybean protein) against ACE was much higher than that of LL (Leu-Leu), although they had similar hydrophobic and predicted activity values. It was difficult to reveal the deep molecular mechanism underlying this phenomenon by traditional experimental methods. The Apo and two complex systems (i.e., ACE–LL and ACE–IY) were therefore subjected to 1 μs long Gaussian accelerated molecular dynamics (GaMD) simulations. The results showed that the binding of IY can cause obvious contraction of the active site of ACE, mainly manifested by a significant lateral shift of α13, α14, and α15. In addition, hinge 2 and hinge 3 were more stable in the ACE–IY system, while these phenomena were not present in the ACE–LL system. Moreover, the α10 of the IY-bound ACE kept an inward state during the simulation progress, which facilitated the ACE to remain closed. However, for the LL-bound ACE, the α10 switched between two outward states. To sum up, our study provides detailed insights into inhibitor-induced conformational changes in ACE that may help in the design of specific inhibitors targeting ACE for the treatment of hypertension.

Effects of Ramipril on the Aldosterone/Renin Ratio and the Aldosterone/Angiotensin II Ratio in Patients With Primary Aldosteronism

The aldosterone/renin ratio (ARR) is currently considered the most reliable approach for case detection of primary aldosteronism (PA). ACE (Angiotensin-converting enzyme) inhibitors are known to raise renin and lower aldosterone levels, thereby causing false-negative ARR results. Because ACE inhibitors lower angiotensin II levels, we hypothesized that the aldosterone/equilibrium angiotensin II (eqAngII) ratio (AA2R) would remain elevated in PA. Receiver operating characteristic curve analysis involving 60 patients with PA and 40 patients without PA revealed that the AA2R was not inferior to the ARR in screening for PA. When using liquid chromatography-tandem mass spectrometry to measure plasma aldosterone concentration, the predicted optimal AA2R cutoff for PA screening was 8.3 (pmol/L)/(pmol/L). We then compared the diagnostic performance of the AA2R with the ARR among 25 patients with PA administered ramipril (5 mg/day) for 2 weeks. Compared with basally, plasma levels of equilibrium angiotensin I (eqAngI) and direct renin concentration increased significantly (P<0.01 or P<0.05) after ramipril treatment, whereas eqAngII and ACE activity (eqAngII/eqAngI) decreased significantly (P<0.01). The changes of plasma renin activity and plasma aldosterone concentration in the current study were not significant. On day 14, 4 patients displayed false-negative results using ARR_direct renin concentration (plasma aldosterone concentration/direct renin concentration), 3 of whom also showed false-negative ARR_plasma renin activity (plasma aldosterone concentration/plasma renin activity). On day 15, 2 patients still demonstrated false-negative ARR_plasma renin activity, one of whom also showed a false-negative ARR_direct renin concentration. No false-negative AA2R results were observed on either day 14 or 15. In conclusion, compared with ARR which can be affected by ACE inhibitors causing false-negative screening results, the AA2R seems to be superior in detecting PA among subjects receiving ACE inhibitors.

Studies on the Interaction between Angiotensin-Converting Enzyme (ACE) and ACE Inhibitory Peptide from Saurida elongata

Angiotensin-converting enzyme (ACE) inhibitory peptides derived from food protein exhibited antihypertensive effects by inhibiting ACE activity. In this work, the interaction between ACE inhibitory peptide GMKCAF (GF-6) and ACE was studied by isothermal titration calorimetry (ITC), molecular docking, ultraviolet absorption spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy. Experimental results revealed that the binding of GF-6 to ACE was a spontaneous exothermic process driven by both enthalpy and entropy. The interaction occurred via a static quenching mechanism and involved the alteration of the conformation of ACE. In addition, ITC and molecular docking results indicated binding of GF-6 to ACE via multiple binding sites on the protein surface. This study could be deemed helpful for the better understanding of the inhibitory mechanism of ACE inhibitory peptides.

Hyponatremic hypertensive syndrome - a retrospective cohort study

AIM

To ascertain the frequency of hyponatremic hypertensive syndrome (HHS) in a cohort of children with hypertensive emergency in a tertiary pediatric hospital.

METHODS

A retrospective review was undertaken among children with hypertensive emergency admitted in our tertiary children hospital between June 2014 and December 2015 with an aim to identify any children with HHS. Three children with HHS were identified during this period.

RESULTS

The 3 patients with HHS presented with hypertensive emergency. They were initially managed with Labetalol infusion and thereafter switched to oral anti-hypertensives (combination of Nifedipine sustained release, Hydralazine and Beta Blocker). All 3 were diagnosed to have unilateral renal artery stenosis. One child was lost to follow up, whereas the other 2 underwent renal angioplasty which was followed with normalization of blood pressure.

CONCLUSION

Despite activation of renin angiotensin axis secondary to renal artery stenosis, these groups of children have significant hyponatremia. Renal re-vascularisation produces excellent results in most of them.

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Regression of a large congenital hepatic arteriovenous malformation

Congenital hepatic arteriovenous malformations are rarely seen in association with persistent neonatal pulmonary hypertension. We report the case of a full-term female newborn who presented with heart failure and respiratory distress soon after birth. Echocardiographic investigation revealed severe persistent pulmonary hypertension and patent ductus arteriosus. Here we report spontaneous regression in size of both the feeder vessel and the vascular bed of the congenital hepatic arteriovenous malformation. We postulate that our conservative use of oral heart failure therapy, in the form of diuretic agents and captopril, decreased the congestion and diameter of the affected vessels.

Stability and cytotoxicity of angiotensin-I-converting enzyme inhibitory peptides derived from bovine casein

This study investigated the effect of heat treatment combined with acid and alkali on the angiotensin-I-converting enzyme (ACE) inhibitory activity of peptides derived from bovine casein. The free amino group content, color, and cytotoxicity of the peptides were measured under different conditions. When heated at 100 °C in the pH range from 9.0 to 12.0, ACE inhibitory activity was reduced and the appearance of the peptides was significantly darkened. After thermal treatment in the presence of acid and alkali, the free amino group content of ACE inhibitory peptides decreased markedly. High temperature and prolonged heating also resulted in the loss of ACE inhibitory activity, the loss of free amino groups, and the darker coloration of bovine casein-derived peptides. However, ACE inhibitory peptides, within a concentration range of from 0.01 to 0.2 mg/ml, showed no cytotoxicity to Caco-2 and ECV-304 cell lines after heat treatment. This indicated that high temperature and alkaline heat treatment impaired the stability of bovine casein-derived ACE inhibitory peptides.

Synthesis and evaluation of chalcone analogues based pyrimidines as angiotensin converting enzyme inhibitors

Hypertension is a widespread and frequently progressive ailment that imparts a foremost threat for cardiovascular and renal disorders. Mammoth efforts are needed for the synthesis of innovative antihypertensive agents to combat this lethal disease. Chalcones have shown antihypertensive activity through inhibition of Angiotensin Converting Enzyme (ACE). Hence, a series of chalcone analogues is synthesized and used as precursor for the synthesis of novel series of pyrimidines. Precursor chalcones were prepared by reacting aldehydes and ketones in presence of sodium hydroxide followed by synthesis of corresponding pyrimidines by reaction with urea in presence of potassium hydroxide. Both groups were then evaluated for their effects on ACE. The results depicted that pyrimidines were more active than chalcones with methoxy (C5 and P5) substitution showing best results to inhibit ACE. Given that chalcone analogues and pyrimidines show a potential as the angiotensin converting enzyme inhibitors.

Purification and characterization of a novel angiotensin-I converting enzyme (ACE) inhibitory peptide derived from enzymatic hydrolysate of grass carp protein

Peptides inhibiting angiotensin-I converting enzyme (ACE, EC. 3.4.15.1) are possible cures of hypertension. Food-derived ACE-inhibitory peptides are particularly attractive because of reduced side effects. Previously, we reported ACE-inhibitory activity of grass carp protein hydrolysates. In this work, we report steps for purifying the ACE-inhibitory peptide from the hydrolysate and its biochemical properties. Following steps of ultrafiltration, macroporous adsorption resin, and two steps of reversed phase high performance liquid chromatography (RE-HPLC), a single Val-Ala-Pro (VAP) tripeptide was identified. The tripeptide with excellent ACE-inhibitory activity (IC(50) value of 0.00534 mg/mL) was a competitive ACE inhibitor and stable against both ACE and gastrointestinal enzymes of pepsin and chymotrypsin. This is the first report of food-derived VAP. The identified unique biochemical properties of VAP may enable the application of grass carp protein hydrolysates as a functional food for treatments of hypertension. The developed purification conditions also allow the production of VAP for pharmaceutical applications.

Laboratory investigation of primary aldosteronism

Availability and wider application of the plasma aldosterone/renin ratio (ARR) as a screening test for primary aldosteronism (PA) has led to the recognition that PA is the most common potentially curable and specifically treatable form of hypertension, possibly accounting for as many as 5-13% of patients. Aldosterone excess also has adverse cardiovascular consequences that go above and beyond hypertension development. These findings support the concept that PA plays an important role in cardiovascular disease states and should be systematically sought and specifically treated, and have led to the development of a US Endocrine Society clinical guideline for the detection, diagnosis and management of this condition. Reliable detection requires that interfering factors (including medications known to alter the ratio) are controlled before ARR measurement (or their effects taken into account), and reliable methods such as fludrocortisone suppression testing are used to confirm PA. Because computed tomography frequently misses aldosterone-producing adenomas yet demonstrates non-functioning nodules, adrenal venous sampling is the only dependable way to differentiate unilateral (surgically correctable) from bilateral (usually treated with aldosterone antagonist medications) forms of PA. For the glucocorticoid-remediable form of PA (familial hyperaldosteronism type I), genetic testing for the causative 'hybrid' 11beta-hydroxylase/aldosterone synthase gene has greatly facilitated detection. Laboratory assessment (including suppression testing post-operatively, and renin measurement during treatment with aldosterone antagonist medications) can assist in assessing therapeutic responses and in guiding ongoing management. Development of new, highly reliable high-throughput mass spectrometric methods for measuring aldosterone and renin should further enhance detection and reliability of diagnostic workup for PA.

Converting enzyme inhibition in mild and moderate essential hypertension. I. Acute effects on blood pressure, the renin-angiotensin system and blood bradykinin after a single dose of captopril

The acute effects of 25 mg captopril on blood pressure, heart rate, components of the renin-angiotensin system and blood concentration of bradykinin were followed in a single-blind placebo study of untreated (group A, n = 15) and thiazide-treated (group B, n = 13) patients with mild or moderate essential hypertension. A drug-related fall in blood pressure was seen in both groups. The blood pressure reduction was more marked in group B than in group A. Heart rate remained unchanged. Plasma concentrations of angiotensin II decreased significantly with concurrent increases in plasma concentrations of renin and angiotensin I, indicating the in vivo inhibition of converting enzyme. Blood concentrations of bradykinin showed no systemic changes. The magnitude of blood pressure reduction was correlated both with the pretreatment levels and the concurrent decreases in plasma angiotensin II. Inhibition of angiotensin II formation can explain a large part of the acute hypotensive pharmacological action of captopril. Other vasoactive systems may be involved. The kallikrein-kinin system does not appear to participate as indicated by the unchanged concentrations of kinin in blood.

Converting enzyme inhibition in mild and moderate essential hypertension. II

In 24 patients with mild/moderate essential hypertension, we studied the effects of captopril with/without hydrochlorothiazide (Htz) on blood pressure, the renin-angiotensin system, blood bradykinin concentration (BBK), plasma volume, exchangeable sodium and glomerular filtration. Daily captopril doses of 75 and 150 mg were equally effective in reducing the blood pressure. Addition of Htz caused further blood pressure reductions. Nineteen patients attained a diastolic blood pressure less than or equal to 90 mmHg. Angiotensin converting enzyme inhibition with captopril led to a fall in plasma concentrations of angiotensin II (PAII) and renin substrate, and an increase in plasma concentrations of renin and angiotensin I. Patients starting with Htz had a higher PAII and subsequently a larger fall in blood pressure on captopril than untreated patients. BBK remained unchanged, indicating that the hypotensive action of captopril does not involve an accumulation of circulating kinin. Body fluid volumes and renal function were not affected by the various treatment regimens.

Vascular haemodynamic effects of perindopril in essential hypertension

Perindopril is an orally active non-thiol angiotensin-converting enzyme (ACE) inhibitor that is hydrolysed by esterases to a biologically active diacid metabolite. Perindopril decreases plasma concentrations of angiotensin II, increases plasma renin activity and reduces systolic and diastolic blood pressure in patients with essential hypertension. Most data support the hypothesis that the beneficial haemodynamic effects of perindopril are caused by ACE inhibition and the consequent reduction in angiotensin II, which either directly or indirectly results in dilatation of peripheral vessels and reduced vascular resistance. The marked blood pressure reduction after perindopril administration in hypertensive patients has not been accompanied by significant changes in heart rate. Furthermore, the lack of reflex tachycardia does not appear to be related to a reduction in baroreceptor sensitivity.

Pharmacokinetics of ramipril in hypertensive patients with renal insufficiency

In an open trial, the pharmacokinetics of ramipril and its active metabolite ramiprilat were studied in 25 hypertensive patients with various degrees of renal insufficiency given 5 mg ramipril p.o. for 14 days. Ramipril was rapidly absorbed and reached a peak concentration after 1-2 h. Cmax was greater in patients with severe renal insufficiency, which might indicate a reduced renal elimination rate, although, the rapid decline of the concentration-time curve for ramipril was almost independent of renal function. The mean initial apparent half-lives on Days 1 and 12, respectively, were 2.8 and 3.4 h (Group I: creatinine clearance 5-15 ml/min), 1.8 and 2.3 h (Group II: creatinine clearance 15-40 ml/min), and 1.9 and 1.9 h (Group III: creatinine clearance 40-80 ml/min). No accumulation was observed after multiple dosing. In contrast, the kinetics of its active acid metabolite ramiprilat was significantly influenced by renal function. The mean times to the peak plasma concentration were 5.7 h in Group I, 4.4 h in Group II and 3.8 h in Group III. The initial decline in plasma ramiprilat was dependent upon renal function; the mean initial apparent half-lives (Days 1 and 12, respectively) were 16.0 and 14.8 h (Group I), 10.1 and 9.5 h (Group II) and 10.6 and 8.0 h (Group III). Mean trough concentrations and absolute accumulation also increased with worsening renal function, and the renal clearance of ramiprilat was significantly correlated with the creatinine clearance. The subsequent long terminal phase at low plasma ramiprilat concentrations represented slow dissociation of the ACE-inhibitor complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of plasma renin activity by captopril in renovascular hypertensive conscious dogs

The increase in plasma renin activity induced by captopril is used in the clinical evaluation of renovascular hypertensive patients. This increase in plasma renin activity could result from either the concomitant fall in systemic pressure or other effects of captopril, such as the removal of an angiotensin II inhibitory effect on renin release, the increased production of bradykinin or prostaglandins, etc. To examine the effect captopril has on plasma renin activity, independent of changes in systemic pressure, captopril (5, 10 and 50 micrograms/kg iv) was administered to conscious dogs before and following the development of 1 clip-2 kidney Goldblatt hypertension. Plasma renin activity, under normal conditions remained unchanged, while during hypertension it increased 2.0, 2.8 and 3.5 fold respectively in response to the three doses of captopril. These results suggest that the development of renovascular hypertension sensitized the kidney to release renin when challenged by captopril and that the effect is independent of changes in systemic pressure.

Captopril in heart failure secondary to a left to right shunt

Captopril was used in 20 infants aged less than 1 year with heart failure secondary to defects with predominantly a left to right shunt that was poorly controlled with digoxin and diuretics. Total daily dose of captopril ranged from 0.88 to 2.5 mg/kg (mean 1.3 mg/kg) in three divided doses. Improvement in the control of heart failure was seen mainly as an increase in the rate of weight gain from a mean of 48 g/week before treatment to 102 g/week on treatment and a decrease in the mean respiratory rate from 68 breaths/minute to 60 breaths/minute. Side effects were seen in four patients--two with asymptomatic mild hypotension, one with renal insufficiency which improved with a reduction in dose, and one with severe oliguria progressing to renal failure. Significant changes in plasma electrolyte concentration did not occur except in the infant who developed acute renal failure.

Total body electrolyte composition in patients with heart failure: a comparison with normal subjects and patients with untreated hypertension

Total body elemental composition was measured in 40 patients with well documented heart failure who were oedema-free on digoxin and diuretics. The results were compared with values for 20 patients with untreated essential hypertension matched for height, weight, age, and sex. Total body potassium alone was also measured in 20 normal subjects also matched for anthropomorphic measurements. Patients with hypertension had a very similar total body potassium content to that of normal subjects, but patients with heart failure had significantly reduced total body potassium. This could not be explained by muscle wasting because total body nitrogen, largely present in muscle tissue, was well maintained. When total body potassium was expressed as a ratio of potassium to nitrogen mass a consistent depletion of potassium was revealed in the group with heart failure. Potassium depletion was poorly related to diuretic dose, severity of heart failure, age, or renal function. Activation of the renin-angiotensin-aldosterone system was, however, related to hypokalaemia and potassium depletion. Such patients also had significantly lower concentrations of serum sodium and blood pressure. Serum potassium was related directly to total body potassium. Despite the absence of clinically apparent oedema total body chlorine was not consistently increased in heart failure, but the calculated extracellular fluid volume remained expanded in the heart failure group. Total body sodium was significantly increased in patients with heart failure, but less than half of this increase could be accounted for by extracellular fluid volume expansion. Potassium depletion in heart failure may account in part for the high frequency of arrhythmias and sudden death in this condition.

Clinical, haemodynamic, and antiarrhythmic effects of long term treatment with amiodarone of patients in heart failure

Twenty two patients with heart failure were studied in a double blind crossover trial to compare amiodarone (200 mg/day) with placebo. Each agent was given for three months. Extrasystoles and complex ventricular arrhythmias were common during ambulatory electrocardiographic monitoring and during exercise testing at entry to the study. Breathlessness and tiredness as assessed by visual analogue scores and duration of treadmill exercise did not become worse during amiodarone treatment. During the placebo and amiodarone phases of the study left ventricular ejection fraction and cardiac index determined by first pass radionuclide ventriculography were similar, both at rest and during upright bicycle exercise. Exercise induced ventricular tachycardia was abolished and simple and complex ventricular arrhythmias observed on 24 hour ambulatory monitoring were greatly diminished during amiodarone treatment. Three patients died, all suddenly, during the placebo phase. In two patients amiodarone was withdrawn after a further myocardial infarction in one and a worsening of symptoms of ventricular arrhythmia in the other. In contrast with other antiarrhythmic agents amiodarone is effective in suppressing ventricular arrhythmias in heart failure without causing adverse haemodynamic effects. Because frequent ventricular arrhythmias are known to be associated with a poor prognosis in heart failure, these data suggest that amiodarone may improve the poor prognosis in patients with heart failure.

Pharmacokinetics and effects on the renin-angiotensin system of ramipril in elderly patients

Converting enzyme inhibitors are likely to be prescribed with increasing frequency in elderly patients. The pharmacokinetics of ramipril, a new potent long-acting non-sulphydryl converting enzyme inhibitor, and its effects on blood pressure, plasma renin activity and angiotensin II concentrations were studied in a group of 8 elderly volunteers (mean age 77, range 61 to 84). Circulating concentrations of the active diacid formed from its parent drug were consistently higher in this group despite apparently normal renal function, assessed by serum creatinine and urea concentrations, compared with younger volunteers (age range 21 to 30). The initial dose of ramipril should be lower in older subjects. The study emphasizes the importance of careful extrapolation of data obtained from young volunteers to older subjects.

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.

Specific measurement of angiotensin metabolites and in vitro generated angiotensin II in plasma

Combining high-performance liquid chromatography with radioimmunoassay enabled the precise measurement of different angiotensins and their metabolites in plasma. Peptides were extracted from 2 ml of plasma by reversible adsorption to phenylsilyl-silica, separated by isocratic high-performance liquid chromatography, and quantitated by radioimmunoassay using a sensitive but suitably cross-reacting angiotensin II antiserum. For the C-terminal angiotensin II metabolites (2-8)heptapeptide, (3-8)hexapeptide, and (4-8)pentapeptide, overall recoveries of 10 fmol peptide added to 1 ml of plasma were (mean +/- SD), 74 +/- 6, 68 +/- 8, and 67 +/- 11%, respectively. The detection limit for these peptides in plasma was 0.2 fmol/ml. Blanks were below the detection limits. In eight seated normal subjects treated for 4 days with enalapril, 20 mg p.o., q.d., angiotensin II metabolites tended to decrease during the 4 postdrug hours. However, their cumulated concentration in relation to octapeptide increased from 54 to 163% on Day 1 and from 62 to 103% on Day 4. After 4 hours of converting enzyme inhibition with enalapril there was still a close correlation between plasma renin activity and angiotensin-(1-8)octapeptide level (r = 0.83, p less than 0.05) and between blood angiotensin I and angiotensin-(1-8)octapeptide levels (r = 0.86, p less than 0.01). Adding angiotensin I in vitro raised the angiotensin-(1-8)octapeptide levels after incubation at 4 degrees C for 4 hours. Thus, immunoreactive "angiotensin II" does not disappear after converting enzyme inhibition largely because of the cumulated contribution of cross-reacting metabolites and partly because of in vitro generation of true angiotensin II.

Effect of captopril on the cerebral circulation in chronic heart failure

Cerebral blood flow (CBF) was investigated in 8 patients with chronic heart failure (CHF) (functional class III) and in twelve controls before and after administration of 6.25 mg and 25 mg captopril, respectively. In four controls, CBF was measured by the intracarotid xenon-133 (133Xe) injection technique using stationary external detectors, while inhalation of 133Xe and single photon emission computer tomography was used in the remaining cases. In the control group, the cerebral metabolic rate for oxygen was calculated from measurements of the arterio-venous oxygen difference as well. Mean CBF was significantly (P less than 0.01) lower in the patients with CHF as compared to our controls. Following captopril administration the mean arterial blood pressure decreased in the CHF patients, ranging from 5 to 40%. Three patients showed decreases of blood pressure to values of 56, 65, and 76 mm Hg, but no symptoms of cerebral hypoperfusion were elicited. CBF was unchanged after captopril administration, even in the patients showing a marked reduction in blood pressure. In the control group, the blood pressure, CBF and the cerebral metabolic rate for oxygen remained essentially constant following captopril administration. It is concluded that the cerebral circulation is well preserved during captopril treatment of chronic heart failure. This might be explained by a shift of the lower limit of CBF autoregulation towards lower blood pressure levels.

The role of renal hemodynamics in the antihypertensive effect of captopril

To evaluate the role of regional hemodynamics in mediating the long-term depressor effect of the converting enzyme inhibitor, captopril, at a low dose (37.5 mg/day), for 2 weeks, its systemic, renal, and forearm circulatory actions were determined in 12 patients with mild to moderate essential hypertension. After administration of captopril, there was a significant decline in mean blood pressure (average -12.1 +/- 1.9%) accompanied by a decrease in systemic vascular resistance (-9.1 +/- 3.3%), but cardiac output did not change. Although forearm vascular resistance was not altered, renal vascular resistance decreased considerably (-17.1 +/- 5.0%). Moreover, there was a highly significant (r = 0.891) correlation between the changes in mean blood pressure and renal vascular resistance. Plasma renin activity increased after therapy as plasma aldosterone decreased, while plasma norepinephrine slightly increased. The change in renal vascular resistance significantly (r = -0.617) correlated with the pretreatment level of plasma renin activity. These findings suggest that suppression of the renin-angiotensin system in essential hypertension induces selective vasodilation in the renal vasculature, which may play an important role in the long-term antihypertensive effect of the converting enzyme inhibitor. This renal vasodilator action appears to be the feature that distinguishes the converting enzyme inhibitor from conventional vasodilator drugs.

Effects of enalapril in heart failure: a double blind study of effects on exercise performance, renal function, hormones, and metabolic state

Several studies have shown symptomatic and haemodynamic improvement after the introduction of angiotensin converting enzyme inhibitors in patients with heart failure treated with diuretics. The concomitant long term effects of the new orally effective long acting angiotensin converting enzyme inhibitor, enalapril, on symptoms, exercise performance, cardiac function, arrhythmias, hormones, electrolytes, body composition, and renal function have been further assessed in a placebo controlled double blind cross over trial with treatment periods of eight weeks. Twenty patients with New York Heart Association functional class II to IV heart failure who were clinically stable on digoxin and diuretic therapy were studied. Apart from the introduction of enalapril, regular treatment was not changed over the study period; no order or period effects were noted. Enalapril treatment significantly improved functional class, symptom score for breathlessness, and exercise tolerance. Systolic blood pressure was significantly lower on enalapril treatment. Echocardiographic assessment indicated a reduction in left ventricular dimensions and an improvement in systolic time intervals. In response to enalapril, the plasma concentration of angiotensin II was reduced and that of active renin rose; plasma concentrations of aldosterone, vasopressin, and noradrenaline fell. There were significant increases in serum potassium and serum magnesium on enalapril. Glomerular filtration rate measured both by isotopic techniques and by creatinine clearance declined on enalapril while serum urea and creatinine rose and effective renal plasma flow increased. Body weight and total body sodium were unchanged indicating that there was no overall diuresis. There was a statistically insignificant rise in total body potassium, though the increase was related directly to pretreatment plasma renin (r = 0.5). On enalapril the improvement in symptoms, exercise performance, fall in plasma noradrenaline, and rise in serum potassium coincided with a decline in the frequency of ventricular extrasystoles recorded during ambulatory monitoring. Adverse effects were few. In patients with heart failure, enalapril had a beneficial effect on symptoms and functional capacity. The decline in glomerular filtration rate on enalapril may not be beneficial in early heart failure.

A dose-response study of HOE 498, a new non-sulphydryl converting enzyme inhibitor, on blood pressure, pulse rate and the renin-angiotensin-aldosterone system in normal man

The effect of different oral doses of HOE 498, a new non-sulphydryl containing converting enzyme inhibitor, was investigated in a double-blind, placebo-controlled study in normotensive volunteers. Dose-related reductions in serum converting enzyme activity, plasma angiotensin II and aldosterone were seen, greater at 4 h than at 12 h after drug ingestion. Converse dose-related increases in blood angiotensin I and plasma active renin concentration occurred. Falls of angiotensin II were as great with 20 mg as with 50 mg of HOE 498, although the effect was more prolonged with 50 mg. The reductions in concentrations of plasma angiotensin II and serum converting enzyme activity and the increases in plasma renin concentration were correlated with the concentration of HOE 498 - diacid in plasma. Dose-related falls in both supine and erect blood pressure were maximal 2-3.5 h after dosing. Pulse rate increased marginally but insignificantly in the supine; slightly and significantly in the upright position, concomitantly with the blood pressure reduction at all doses of active drug. We conclude that effects of single doses of HOE 498 on the renin-angiotensin system are maximal within 4 h, but are still apparent after 24 h. Thus it is likely that once daily administration will be adequate for treatment of high blood pressure in patients.

Apparently high plasma angiotensin II levels in patients with essential hypertension treated by converting enzyme inhibition

Plasma angiotensin I and II (AI and AII) were measured in 13 patients with essential hypertension before and during chronic treatment with enalapril (MK 421) and in seven subjects during an acute study. Two techniques were used for simultaneous extraction of AI and AII. Despite appropriate correction for cross-reaction of AI with the AII antibody, one of the techniques gave consistently higher AII and lower AI levels in plasma of subjects treated with enalapril. The possibility of in vitro conversion of AI into AII-immunoreactive material during the purification or the radioimmunoassay steps should be considered. The use of the alternative technique is proposed for simultaneous processing of blood samples for AI and AII.

Natriuretic effect and changes in renal haemodynamics induced by enalapril in essential hypertension

The purpose of this study was to evaluate the natriuretic effect and renal haemodynamic changes induced by enalapril in patients with essential hypertension. In a group of 11 patients with mild to moderate hypertension with normal renal function, and on a controlled sodium intake (80 mmol/day), a decrease in systolic and diastolic blood pressure was observed (p less than 0.001) after 16 weeks of enalapril treatment (20 mg/day), without a change in heart rate. An increase in plasma renin activity (p less than 0.05) without changes in serum aldosterone, and a decrease in exchangeable sodium (p less than 0.001) were present at the end of the treatment period. In 10 hypertensive patients also taking a dietary sodium of 80 mmol/day, the renal haemodynamics, humoral changes, and urinary sodium excretion were measured during 4 days of enalapril treatment (20 mg/day). There was an increase in urinary sodium excretion on the 3rd and 4th days of treatment (p less than 0.01). The effective renal plasma flow and fractional sodium excretion increased 72 hours after the beginning of treatment (p less than 0.01); the glomerular filtration rate did not change, and filtration fraction decreased at 72 hours. Mean blood pressure fell 2 hours after the first dose (p less than 0.01), and the maximum drop in intrarenal vascular resistance occurred after 72 hours of treatment (p less than 0.01). Plasma renin activity increased (p less than 0.05) and serum aldosterone decreased (p less than 0.01) 2 hours after the first dose. Thereafter, serum aldosterone increased progressively until it reached values similar to those with placebo at 48 and 72 hours of treatment. Urinary kallikrein fell during the 2nd and 3rd day of treatment (p less than 0.01). It was concluded that the decrease in exchangeable sodium was due to a natriuretic effect of enalapril. This effect presumably results from renal haemodynamic changes due to the reduction of angiotensin II. Other mechanisms, such as the reduction of aldosterone and accumulation of kinins, could be contributory factors.

Captopril in heart failure. A double blind controlled trial

The effect of the converting enzyme inhibitor captopril as long term treatment was investigated in 14 patients with severe congestive heart failure in a double blind trial. Captopril reduced plasma concentrations of angiotensin II and noradrenaline, with a converse increase in active renin concentration. Effective renal plasma flow increased and renal vascular resistance fell; glomerular filtration rate did not change. Serum urea and creatinine concentrations rose. Both serum and total body potassium contents increased; there were no long term changes in serum concentration or total body content of sodium. Exercise tolerance was appreciably improved, and dyspnoea and fatigue lessened. Left ventricular end systolic and end diastolic dimensions were reduced. There was an appreciable reduction in complex ventricular ectopic rhythms. Adverse effects were few: weight gain and fluid retention were evident in five patients when captopril was introduced and two patients initially experienced mild postural dizziness; rashes in two patients did not recur when the drug was reintroduced at a lower dose; there was a significant reduction in white cell count overall, but the lowest individual white cell count was 4000 X 10(6)/l. Captopril thus seemed to be of considerable value in the long term treatment of severe cardiac failure.

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)

Enalapril in treatment of hypertension with renal artery stenosis. Changes in blood pressure, renin, angiotensin I and II, renal function, and body composition

The converting enzyme inhibitor enalapril, in single daily doses of 10 to 40 mg, was given to 20 hypertensive patients with renal artery stenosis. The decrease in blood pressure six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II, and to the concurrent decrease in angiotensin II. Blood pressure decreased further with continued treatment; the long-term decrease was not significantly related to pretreatment plasma renin or angiotensin II levels. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low, and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, decreased further. The increase in active renin during long-term treatment was proportionately greater than the increase in angiotensin I; this probably reflects the diminution in renin substrate that occurs with converting enzyme inhibition. Long-term enalapril treatment increased renin secretion by more than 10-fold, and renal venous and peripheral plasma renin concentration by more than 20-fold; however, the mean renal venous renin ratio was not changed. Enalapril caused a reduction in effective renal plasma flow via the affected kidney but a marked and consistent increase on the contralateral side, where renal vascular resistance decreased. The overall increase in effective renal plasma flow was significantly related to the decrease in angiotensin II. Overall glomerular filtration rate was lowered, and serum creatinine and urea increased. Enalapril alone caused a long-term reduction in exchangeable sodium, with slight but distinct increases in serum potassium. In five patients with bilateral renal artery lesions, enalapril given alone for three months did not cause renal function to deteriorate. Enalapril was well tolerated and provided effective long-term control of hypertension; only two of the 20 patients studied required concomitant diuretic treatment.

Enalapril (MK421) and its lysine analogue (MK521): a comparison of acute and chronic effects on blood pressure, renin-angiotensin system and sodium excretion in normal man

The immediate and long-term effects of enalapril (MK421) and its lysine analogue (MK521) in once-daily dosage, were compared in a study of 12 normal subjects. Both compounds lowered blood pressure equally throughout 24 h without causing tachycardia. The biochemical changes with MK521 were more sustained than with MK421, but this did not affect the magnitude of blood pressure reduction. Twenty-four hours after the previous dose, with both active drugs, plasma renin concentration was significantly higher on day 8 than on day 1, though angiotensin I did not increase in proportion; this probably reflects a fall in renin-substrate with prolonged converting enzyme inhibition. There was an early natriuresis with each compound but this effect was no longer apparent after 8 days of continuous therapy. Both MK421 and MK521 were well tolerated with no serious side effects.

The renin-angiotensin system during converting enzyme inhibition with captopril in patients with severe treatment-resistant hypertension

The effect of captopril on blood pressure (BP) and various components of the renin-angiotensin system was assessed in ten severely hypertensive patients. Captopril acutely reduced the BP with a maximum decrease of 23% at 90-120 min. Maintenance treatment with captopril alone could not control the BP in any of the patients. Addition of hydrochlorothiazide markedly reduced the BP, while supplementation with propranolol caused no consistent changes. Three patients attained a supine diastolic blood pressure (SDBP) less than or equal to 90 mmHg. Only two patients had a fall in SDBP less than 10 mmHg. One patient stopped because of taste disturbances. Monitoring the renin-angiotensin system showed suppressed plasma concentrations of angiotensin II and increased levels of angiotensin I and renin, indicating the inhibition of converting enzyme activity. Plasma concentration of renin substrate decreased significantly. This observation has important implications for the methodology of renin assays. Captopril is an effective alternative in the treatment of hypertensive patients not readily controlled with conventional therapy.

Factors related to first dose hypotensive effect of captopril: prediction and treatment

The blood pressure response to the first dose of captopril (6.25 mg, 12.5 mg, or 25 mg) was measured in 65 treated, severely hypertensive patients. Mean supine blood pressure was 187/108 mm Hg immediately before captopril was given. Twenty one patients experienced a fall in supine systolic pressure greater than 50 mm Hg, including five whose pressure fell more than 100 mm Hg and two whose pressure fell more than 150 mm Hg. Six patients developed symptoms of acute hypotension, including dizziness, stupor, dysphasia, and hemiparesis. Percentage reductions in blood pressure were greatest in those with secondary hypertension (p less than 0.05), high pretreatment blood pressure (p less than 0.05), and high concentrations of plasma renin and angiotensin II (p less than 0.01). No significant correlation was found between fall in blood pressure and serum sodium concentration, age, renal function, and the dose of captopril given. A severe first dose effect cannot be consistently predicted in individual patients who have received other antihypertensive drugs for severe hypertension. Such patients should have close medical supervision for at least three hours after the first dose of captopril.

Acute effects of captopril on cardiopulmonary hemodynamics and renin-angiotensin-aldosterone and bradykinin profile in hypertension

Hemodynamic variables were measured and plasma renin activity (PRA), angiotensin II (AII), aldosterone, and bradykinin assays performed in 21 hypertensive men on regular diet and thiazide diuretics before and 60 to 90 minutes after 25 mg oral captopril. Heart rate, right and left ventricular filling pressures, mean cardiac index (CI), and pulmonary vascular resistance (PVR) remained unchanged. The mean intra-arterial pressure (MAP) fell from 140 +/- 5 to 116 +/- 6 mm Hg (p less than 0.001) correlating with reduction of systemic vascular resistance (SVR) (r = 0.87, p less than 0.001), control PRA (r = 0.59, p less than 0.01), and All levels (r = 0.72, p less than 0.005) but not with control bradykinin or its postcaptopril rise (p less than 0.01). The fall in SVR correlated with reduction in plasma All (r = 0.80, p less than 0.001) and aldosterone concentrations (r = 0.53, p less than 0.05). Of four patients (19%) with precipitous fall in MAP after captopril, three needed volume expansion for circulatory support. We conclude: (1) All reduction by captpril and not bradykinin potentiation explains most of the agent's hemodynamic response in hypertensive circulation, (2) endogenous All may have a supportive role for SVR and possibly for CI but not for PVR, and (3) extra precaution is warranted while captopril is being started in patients taking diuretics.

Converting-enzyme inhibitor enalapril (MK421) in treatment of hypertension with renal artery stenosis

Enalapril maleate (MK421), a new inhibitor of angiotensin converting enzyme, in single daily doses of 1.25-40 mg was assessed in five patients with hypertension and renal artery stenosis. Only small falls in plasma angiotensin II concentrations were seen at doses less than 10 mg; even with 10 and 20 mg, angiotensin II concentrations had risen again 24 hours from the last dose. During long-term treatment with 10-40 mg daily all patients achieved good blood-pressure control. No significant changes of body sodium or potassium values were seen. The drug was well tolerated with no serious side effects. These findings are evidence of the efficacy and acceptability of enalapril in the medical management of hypertension with renal artery stenosis.

Captopril treatment: inter-dose variations in renin, angiotensins I and II, aldosterone and blood pressure

1 The ability of captopril, 150 mg three times daily by mouth, to effect sustained reduction in plasma angiotensin II, with converse increases in circulating angiotensin I, and in active, inactive and total renin concentrations, has been assessed. 2 During prolonged treatment with captopril alone, and 12 h after the last dose of the drug, plasma angiotensin II remained approximately one-sixth of basal concentrations, while angiotensin I and renin concentrations were proportionately increased. However, further increases in angiotensin I, and in active, inactive and total renin concentrations, were seen 2 and 6 h after the morning dose of 150 mg captopril. 3 Inter-dose variations in plasma aldosterone and blood pressure were not closely related to concurrent variations in the renin-angiotensin system. 4 Arguments are presented for relying on measurements of plasma renin and angiotensin concentrations rather than of renin activity or aldosterone in assessing the effectiveness of converting enzyme inhibition.

Captopril in the management of hypertension with renal artery stenosis: its long-term effect as a predictor of surgical outcome

Fifteen patients with hypertension and unilateral renal artery disease were treated with captopril alone; 10 came to operation and were later assessed postoperatively with no drug treatment. Captopril caused both immediate and sustained decreases in plasma angiotensin II and aldosterone, with increases in plasma active renin and blood angiotensin I concentrations. Decrements in systolic and diastolic pressure 2 hours after the first dose of captopril were closely correlated with the initial decreases in plasma angiotensin II. Blood pressure was decreased by long-term captopril therapy irrespective of whether plasma angiotensin II was abnormally high before treatment. The long-term response of both systolic and diastolic pressure correlated well with the response to surgery. By contrast, the blood pressure decrease 2 hours after the initial dose of captopril variously underestimated and overestimated the decrease during prolonged use of the drug and did not relate to surgical outcome. In patients who, before treatment, had secondary aldosteronism, hyponatremia, hypokalemia and sodium and potassium deficiency, captopril corrected these abnormalities. In the remaining patients, long-term captopril therapy did not alter exchangeable sodium, plasma sodium or total body potassium, although plasma potassium levels increased.

Captopril in renovascular hypertension: long-term use in predicting surgical outcome

The angiotensin converting-enzyme inhibitor captopril was used as long-term preoperative treatment in a series of hypertensive patients with unilateral renal arterial disease. There were immediate and sustained falls in plasma angiotensin II and aldosterone concentrations, with converse increases in circulating renin and angiotensin I. In patients with sodium and potassium deficiency and secondary aldosterone excess before treatment captopril corrected the sodium and potassium deficits; in these cases the initial hypotensive response was profound but the later effect was less pronounced. When sodium and potassium state was initially normal it remained unchanged during captopril treatment, while the full hypotensive effect took up to three weeks to be attained. The immediate, but not long-term, falls in arterial pressure with captopril were proportional to the immediate decrements of plasma angiotensin II. Nevertheless, while the immediate blood-pressure reduction with captopril variously overestimated and underestimated the eventual surgical response, the absolute blood-pressure values during long-term captopril related well with those after operation. Pretreatment plasma renin and angiotensin II concentrations, while closely predicting the immediate captopril response, are fallible guides to surgical prognosis. In contrast, long-term treatment with converting-enzyme inhibitors may provide an accurate indication of surgical outcome.

[Captopril in congestive heart failure (author's transl)]

Captopril (Lopirin, Squibb, von Heyden) is an inhibitor of the angiotensin-I converting enzyme. In congestive heart failure angiotensin mediated vasoconstriction and aldosterone secretion is reversed by captopril. Both effects of captopril induce reduction of cardiac preload and afterload. The clinical state of patients with congestive heart failure therefore improves since cardiac output increased and pulmonary pressures decrease. Captopril acts orally and the dosage used for the treatment of congestive heart failure ranges from 50 to 150 mg daily. After oral ingestion of a single dose the maximum haemodynamic effect is observed after 45-90 min. No tolerance induction or tachyphylaxis has been observed during maintenance therapy over a period of 18 months. There are some reversible adverse reactions like pruritus, skin rash and partial or complete taste loss which are dose related. Serious side effects include leucopenia, agranulocytosis, renal failure and membranous glomerulonephritis. Therefore regular urinary and blood analysis is necessary during captopril therapy.

Captopril: clinical pharmacology and benefit-to-risk ratio in hypertension and congestive heart failure

Captopril, a competitive antagonist of angiotensin converting enzyme, has been marketed in the United States for the treatment of resistant hypertension. Despite extensive study, its exact mechanism of action remains unclear; decreased renin-angiotensin-aldosterone and sympathoadrenal system activity as well as increased bradykinin and prostaglandin E and F activity have been postulated. The drug decreases peripheral vascular resistance. Controlled trials in resistant hypertension of various etiologies and chronic congestive heart failure have demonstrated sustained effectiveness and therapeutic benefits. Side effects include skin rash, loss of taste, proteinuria, and leukopenia; higher doses and concomitant renal dysfunction appear to be predisposing factors. The benefit-to-risk ratio for captopril clearly justifies its use in resistant cases of hypertension and congestive heart failure, but further experience is needed to evaluate its use in milder forms of these diseases.