RESPONSES OF PLASMA ADRENOCORTICAL STEROIDS TO LOW-DOSE ACTH IN NORMAL SUBJECTS

OBJECTIVE The standard ACTH test in clinical use employs a pharmacolog ical dose of ACTH which assesses the maximum secretory capacity of the adrenal cortex. We have investigated the responses of plasma adrenoco rtical steroids including cortisol, aldosterone and dehydroepiandroste rone (DHEA) to physiological doses of ACTH (ACTH 1-24, tetracosactide, Cortrosyn) and determined the minimal dose which induces a response e quivalent to that induced by a pharmacological dose of ACTH. DESIGN Ra pid ACTH tests at various physiological (0.1, 0.5 , 1 and 5 mu g) and standard pharmacological (250 mu g) intravenous doses. SUBJECTS Seven healthy normal volunteers. MEASUREMENTS Plasma cortisol, aldosterone a nd DHEA were measured. Peak value and the increment from basal value w ere used as indices of responses. RESULTS Each steroid responded to ph ysiological doses of ACTH in a dose dependent manner. The minimum dose inducing an equivalent response to 250 mu g ACTH was 0.5 mu g for pea k and incremental values in cortisol and DHEA, while that for aldoster one was 0.1 mu g The time to peak for each steroid was delayed as the dose increased. Plasma aldosterone and DHEA peaked significantly earli er than plasma cortisol in 1-5 mu g and 0.5-5 mu g ACTH tests, respect ively. CONCLUSIONS These results suggest that the sensitivity of secre tion to physiological doses of ACTH in descending order is aldosterone > DHEA=cortisol. When peak and incremental values are used, sufficien t doses of ACTH are 0.1 mu g for plasma aldosterone and 0.5 mu g for p lasma cortisol and DHEA in the rapid ACTH test.