The involvement of the calcium messenger system in the control of steroidogenesis in the rat and bovine adrenal cortex has been studied extensively. However the role of these second messengers in the control of human adrenocortical function is not established. This was therefore studied by incubating collagenase-dispersed human adrenocortical cells with the calcium ionophore A23187 and the protein kinase C activator phorbol 12-myristate 13-acetate (TPA). The effects of the calcium channel blocker verapamil on basal and stimulated steroidogenesis were also studied.
Both TPA (1 pmol/l–10 μmol/l) and A23187 (1 nmol/l–10 μmol/l) caused a dose-dependent increase in cortisol, aldosterone and corticosterone production. Verapamil (10 μmol/l) inhibited the increase in aldosterone, corticosterone and cortisol produced in response to ACTH(1–24), potassium, and desacetyl-αMSH. Unlike previous results in the rat, these effects were not specific for aldosterone secretion.
The results suggest that, as in other species, calcium mobilization and protein kinase C activation have a role in the control of steroidogenesis in the human adrenal cortex. However, in contrast to the rat, these mechanisms appear to be involved in the control of steroidogenesis in both the zona glomerulosa and inner zone cells.