Mineralocorticoid response to low dose adrenocorticotropin infusion

The adrenocorticoid responses to low dose ACTH of plasma aldosterone (aldo), corticosterone (B), 11-deoxycorticosterone (DOC), 18-hydroxycorticosterone (18-OHB), 18-hydroxycorticosterone (18-OH-DOC), and cortisol (F) were compared. Alpha ACTH-)1-24) was infused beginning at 0800 h at increasing rates from 12.5-200 mIU/30 min in supine normal subjects under the following conditions: 1) regular Na (120 meq) diet, 2) low Na (10 meq) diet, 3) dexamethasone preadministration (0.5 mg every 6 h for 48 h), and 4) night study (2000 h; 120 meq Na intake). Plasma 18-OH-DOC and B demonstrated quantitatively the greatest responses to ACTH, while DOC and 18-OHB responses were intermediate. Increments in aldo and F were least after ACTH and were maximum at 50 mIU/30 min ACTH, whereas other corticosteroids demonstrated linear responses up to infusion rates of 200 mIU/30 min. All corticosteroids, however, were similar in their threshold responses to ACTH which were at infusion rates of approximately 7-9 mIU/30 min. Na restriction enhanced aldo and 18-OHB responses to ACTH 2- to 3-fold but did not alter the other corticosteroid responses. Dexamethasone pretreatment augmented aldo, 18-OHB, and F responses but did not change the responsitivity of the other corticosteroids to ACTH. Adrenal corticosteroid responses to ACTH were not significantly different between 0800 and 2000 h in subjects on 120-meq Na intake. Thus, corticosteroids show markedly different responses to physiological doses of ACTH, which may have more importance in their regulation than heretofore proposed. Dexamethasone pretreatment enhances aldo, 18-OHB, and F responses to ACTH but does not affect the responses of other corticosteroids. Contrary to reports in experimental animals, corticosteroid responses to ACTH in man do not differ from day to night.