Studies of the control of plasma aldosterone concentration in normal man. 3. Response to sodium chloride infusion

The peripheral plasma levels of aldosterone, renin activity, potassium, sodium, corticosterone, and cortisol were measured in six normal subjects four times daily-10 a.m., 2 p.m., 5 p.m., 11 p.m.-on 3 consecutive days. A constant daytime activity program was maintained throughout the study. After 5 days on a 10 mEq sodium/100 mEq potassium isocaloric intake, the mean upright 10 a.m. plasma renin activity was 1773+/-186 ng/100 ml per 3 hr and the mean plasma aldosterone, 81+/-14 ng/100 ml. These two parameters fell continuously throughout the day parallel to the fall in plasma cortisol and corticosterone. In response to 2 liters of normal saline infused from 10 a.m. to 2 p.m. on 2 consecutive days, plasma aldosterone levels fell significantly to 13+/-5 ng/100 ml at 2 p.m. after the 1st day's infusion and to 6+/-1 ng/100 ml at 2 p.m. after the 2nd. Plasma renin activity demonstrated a parallel fall to 368+/-63 ng/100 ml per 3 hr and 189+/-27 ng/100 ml per 3 hr at 2 p.m. on the 1st and 2nd days, respectively. There was no significant alteration in plasma levels of cortisol, corticosterone, potassium, or sodium on the 2 days of sodium loading in comparison with the control day. In an additional study, five normal supine subjects received 500 ml saline/hr for 6 hr. As in the 2 day study, plasma aldosterone and renin activity had parallel decrements at 1, 2, 4, and 6 hr after the start of the saline infusion. From these studies, it is concluded that plasma renin activity is the dominant factor controlling plasma aldosterone when sodium-depleted normal subjects are acutely repleted.