Role of calcium ion in acth-induced steroidogenesis in humans

In order to examine the role of calcium ion in ACTH-induced steroidogenesis in humans, we carried out infusion of a pharmacological dose of ACTH (4.2 micrograms/kg) and a physiological dose of ACTH (0.0084 microgram/kg) for 120 min, and infusion of dibutyryl cyclic AMP (DBcAMP) [0.33 mg/kg/min] for 20 min, in 22 normal subjects with or without verapamil treatment (360 mg/day, orally) for 5 days. The subjects were pretreated with 1.0 mg of dexamethasone and 5.0 mg of enalapril daily for 2 days before each infusion test to inhibit endogenous ACTH and angiotensin II. Following infusion of 0.0084 microgram/kg of ACTH, plasma levels of corticosterone (P less than 0.02) and cortisol (P less than 0.01) were significantly increased; with chronic verapamil treatment plasma levels of corticosterone (P less than 0.05) and cortisol (P less than 0.02) were significantly lower than those without verapamil. On the other hand, 4.2 micrograms/kg of ACTH for 120 min significantly increased the plasma levels of several steroid hormones, although there were no differences between the infusion with and without verapamil. Infusion of DBcAMP for 20 min significantly increased plasma levels of corticosterone (P less than 0.02) and cortisol (P less than 0.01), but verapamil did not affect the steroidogenic response to the DBcAMP infusion. The present results suggest that steroidogenesis induced by a physiological dose of ACTH differs from that after a pharmacological dose of ACTH or DBcAMP, and is mediated mainly by calcium ion as an intracellular messenger in man.