Effect of angiotensin converting enzyme inhibition on blood pressure, plasma renin activity and plasma aldosterone in essential hypertension

An angiotensin converting enzyme inhibitor was administered to 15 patients with essential hypertension after periods of sodium depletion and repletion, and the responses of blood pressure, plasma renin activity, and plasma aldosterone were recorded in the supine and erect position. After Na depletion the converting enzyme inhibitor induced significant fall of blood pressure in the supine position in all patients; in the erect position, 5 patients became hypotensive whereas the remaining exhibited increases in blood pressure to variable degree. After Na repletion, the converting enzyme inhibitor induced a lesser fall in blood pressure in 3 patients in the supine position, whereas in the erect position all patients exhibited increases in blood pressure. Plasma renin activity rose after injection of the inhibitor in all patients in both phases and was further stimulated by the upright posture. Plasma aldosterone declined after injection in both phases in the supine position. However, in the erect position aldosterone rose by up to 400%. This increase was significantly correlated with the percent increment in plasma renin activity and the elevation of blood pressure, but was mostly observed in patients with lower absolute renin values. In view of the postural increases of blood pressure and plasma aldosterone in spite of continuing converting enzyme blockade, the possible participation of factors other than angiotensin II in regulating these two parameters is discussed.