Direct Inhibitory Effect of Dexamethasone on Steroidogenesis of Human Adrenalin Vivo

Abstract

A rapid ACTH test was used to investigate the direct effect of glucocorticoid on the steroidogenesis by the adrenal cortex in man. The plasma cortisol response to 250 μg iv synthetic a-ACTH-(l–24) (Cortrosyn) was determined in normal subjects pretreated with 2 and 12 mg dexamethasone. The 15- and 30-min increments in plasma cortisol levels in response to ACTH injection after pretreatment with 12 mg dexamethasone were significantly suppressed compared to values obtained after pretreatment with 2 mg dexamethasone. The present study suggests that there is a direct inhibitory effect of glucocorticoid on adrenocortical steroidogenesis in man.