SEQUENTIAL CHANGES IN CIRCULATING LEVELS OF ANGIOTENSIN I AND II, RENIN, AND BRADYKININ AFTER CAPTOPRIL

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Abstract
Venous blood levels of angiotensin I, angiotensin II, bradykinin and renin were measured before, and 30, 60, 90 and 120 minutes after, the administration of Captopril (50 mg) to eight normal subjects. Similar measurements were made in a patient with proved renovascular hypertension. In all subjects, there were significant increases in the levels of renin and angiotensin I, with reciprocal changes in angiotensin II, but no increase in the level of bradykinin. These changes were maximal at 90 minutes. In the patient, blood pressure fell in parallel with the angiotensin II levels. In the normotensive subjects, there was a significant diuresis and natriuresis after the administration of Captopril. Raised levels of circulating bradykinin, with potentiation after Captopril, were measured in an anaesthetized dog given exogenous bradykinin by infusion. These studies indicate that the hypotensive effect of Captopril is not due to raised circulating levels of bradykinin, and suggest a contribution by an intrarenal effect of the drug.