Effects of potassium loading in normal man on dopaminergic control of mineralocorticoids and renin release

The interacting effects of potassium with the dopaminergic control of mineralocorticoid release were evaluated in normal man. Sixteen male healthy volunteers [27 +/- 6 (s.d.) years] on a 200 mmol sodium (Na+) and 60 mmol potassium (K+) diet (control) received a K+ load of 200 mmol/day for 6 days (high-K+ diet). Basal plasma aldosterone and 18-OH-corticosterone (18-OH-B) levels were significantly increased after 6 days of the high-K+ diet, whereas basal levels of 18-OH-deoxycorticosterone (18-OH-DOC) and corticosterone remained unchanged. Fifteen minutes after 10 mg i.v. of the dopaminergic antagonist, metoclopramide, a significant increase was only obtained for basal plasma aldosterone and 18-OH-B levels. The absolute rise of aldosterone and 18-OH-B induced by metoclopramide was greater (P less than 0.01) after K+ supplementation. However, the relative increase of these hormones was similar before and after K+ loading. Basal plasma renin activity increased significantly under high-K+ diet. The results indicate that K+ homeostasis must be taken into account when estimating absolute response of aldosterone and 18-OH-B to dopaminergic antagonism.