Plasma aldosterone and renin activity response to acth infusion in dexamethasone-suppressed normal and sodium-depleted man

AGTH α^1-24 was infused at increasing rates of 12.5-200 mIU/30 min in dexamethasonesuppressed normal subjects while on normal and low sodium diets. The lowest infusion rate of ACTH significantly increased the median plasma cortisol concentration from <1.0/µg/100 ml to 3.1/µg/100 ml (p < 0.01) and the median plasma aldosterone concentration from 4.3 ng/100 ml to 8.8 ng/100 ml (p < 0.025) while on a normal sodium diet. Plasma renin activity was not significantly changed during this period. After sodium restriction the peak median plasma aldosterone response to ACTH was 3.8 times that during normal sodium intake while the plasma cortisol response was unchanged. The median plasma renin activity (PRA) rose from 0.45 to 2.45 ng/ml-hr^-1 during the first two infusion periods. It is estimated from these data that an ACTH infusion rate of 9 mIU/30 min will produce equally significant increases in both plasma cortisol and aldosterone concentrations in such subjects on a regular diet. There was an increased responsiveness of plasma aldosterone to ACTH infusion following sodium restriction which may in part be related to concurrent rises in renin activity. This enhanced response of plasma aldosterone was not totally dependent upon the concurrent rise in PRA since suppression of the latter hormone by infusion of saline failed to abolish the ACTH mediated increase in plasma aldosterone.