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

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.

Captopril does not blunt the sympathoadrenal response to cigarette smoking in normotensive humans

The aim of this study was to assess whether an interaction exists between the renin-angiotensin system and the sympathetic nervous system at the level of the adrenal medulla during smoking in normal humans. Thirteen habitual smoking volunteers were studied in a randomized, single-dose, double-blind, cross-over fashion using 50 mg captopril vs placebo followed by smoking of two high nicotine content cigarettes within 15 min. Blood samples were obtained at frequent intervals before, during and after smoking. We found that the increase in plasma adrenaline concentration during cigarette smoking was modest. There was no difference between captopril treatment as compared to placebo. Thus, the adrenaline response to cigarette smoking was not blunted by acute blockade of angiotensin II generation. A significant increase in heart rate, and blood pressure was found as well. No increase in plasma noradrenaline concentration was found. Plasma renin concentration increased significantly during captopril treatment, whereas it decreased throughout the study period in the placebo phase. Plasma angiotensin II concentration decreased in both the captopril treatment and the placebo phase throughout the study period, but this was more pronounced during captopril treatment. In conclusion, cigarette smoking-induced activation of the sympathetic nervous system was not blunted by acute ACE-inhibition by captopril. This indicates that angiotensin II does not facilitate smoking-induced activation of sympathoadrenal activity in humans.

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.

Captopril enhances insulin responsiveness of forearm muscle tissue in non-insulin-dependent diabetes mellitus

Bradykinin infusion has been shown to improve glucose metabolism in non-insulin-dependent diabetic subjects (NIDD). Therefore, we tested the following hypothesis: inhibition of Kininase II, the bradykinin (BK) degrading enzyme, by captopril may also improve glucose metabolism in NIDD. Immediate effects of captopril on total body and peripheral glucose disposal were examined in five normotensive, normal weight NIDD and compared with five NIDD control subjects, well matched for age, weight and degree of fasting hyperglycaemia. The euglycaemic insulin clamp technique was employed in combination with the forearm catheter technique. After 90 min of insulin infusion a single dose of 25 mg captopril was administered orally, whereas in the control group a placebo was given. Captopril lead to a significant rise in total body glucose disposal and forearm glucose uptake, while in the control group no change was observed. Simultaneously, captopril lead to reduction in muscular release of lactate and pyruvate. We conclude that these results demonstrate the stimulatory effect of captopril on insulin-induced glucose disposal of the whole body, which appears to be a result of increased glucose utilization by peripheral tissues. Because of the described insulin-like activity of bradykinin, the concomitant accumulation of local kinins by captopril-induced inhibition of kininase II may represent an attractive hypothesis to explain the generated data sufficiently.