Angiotensin converting enzyme inhibition reveals an important role for the renin system in the control of normal and high blood pressure in man.

Captopril, given for 5 days to normotensive healthy subjects caused a significant fall in blood pressure. The fall in mean supine blood pressure was greater on a low sodium diet (10 mmols/day) - 19.6% and was less on a high sodium diet (350 mmols/day) - 11% compared to the normal sodium intake (120 mmols/day) when the fall in blood pressure was 16.5%. Patients with essential hypertension who were studied on their normal diet had a similar fall in blood pressure for a given plasma renin activity. It seems likely that the predominant mechanism whereby captopril lowers blood pressure is through the inhibition of the formation of angiotensin II. If this is so, our results suggest that the renin system is an important control of both normal and high blood pressure when on a normal sodium intake.