REGULATION OF 18-OXOCORTISOL AND 18-HYDROXYCORTISOL BY THE RENIN-ANGIOTENSIN SYSTEM AND ACTH IN MAN

Based on urinary excretion studies the secretion of the cortisol deriv atives, 18-oxocortisol and 18-hydroxycortisol are believed to be regul ated by ACTH and to a lesser degree by the renin-angiotensin system. P lasma concentrations of 18-oxocortisol and 18-hydroxycortisol were mea sured during the simultaneous activation of the renin-angiotensin syst em and inhibition of ACTH secretion. Five healthy male subjects consum ing a sodium diet ad libitum were studied. Blood was drawn at 0800 h a fter 1 h in the supine position. In the first set of experiments, the subjects remained in the supine position from 0800 to 1000 h with or w ithout the oral administration of 2 mg dexamethasone at 0800 h. In the second set of experiments the subjects were placed in the upright pos ition after drawing the 0800 h sample. The subjects were studied with and without dexamethasone administered at 0800 h. Blood was drawn agai n at 1000 h. Plasma levels of 18-oxocortisol, 18-hydroxycortisol, ACTH , plasma renin activity (PRA), cortisol, aldosterone and 18-hydroxycor ticosterone were measured by radioimmunoassay. None of these parameter s changed during the 2 h in the supine position. 18-Oxocortisol, 18-hy droxycortisol, aldosterone, 18-hydroxycorticosterone and PRA increased , but ACTH and cortisol did not change when the subjects were placed i n the upright position. After dexamethasone administration, 18-oxocort isol, 18-hydroxycortisol, cortisol, aldosterone and 18-hydroxycorticos terone decreased in the supine position and no increase occurred in 18 -oxocortisol, 18-hydroxycortisol and 18-hydroxycorticosterone in the u pright position. PRA and aldosterone increased and ACTH and cortisol d ecreased in these subjects. 18-Oxocortisol and 18-hydroxycortisol were more dependent on ACTH regulation and less on the renin-angiotensin s ystem than aldosterone.