The effects of captopril on blood pressure in essential hypertensive patients with low or normal plasma renin activity. Interference with autonomic nervous system.

Captopril was administered to 12 essential hypertensive patients with low or normal plasma renin activity in order to evaluate its effectiveness in decreasing blood pressure and to determine whether the inhibition of converting enzyme could interfere with sympathetic neural activity. Captopril, at the doses of 150-450 mg/die, normalized blood pressure in 5 patients (responders) and had no effect on 7 patients (non responders). A significant decrease in heart rate was observed in all patients. Captopril failed to significantly increase plasma renin activity in all patients. Supine plasma levels of catecholamines were significantly higher in responders compared with non responders and decreased significantly after treatment with captopril. The physiological study we performed on all patients suggests an overall integrity of the baroreceptor reflex arc and vascular reactivity to stress before as well as after treatment with captopril. On the contrary, the bradycardia induced by diving test was significantly greater after treatment than before therapy. These findings suggest that the antihypertensive effect of converting enzyme inhibition may be partly due to interference with sympathetic neural activity. Moreover captopril seems to exert an important effect on parasympathetic activity irrespective of blood pressure changes.