Steroidogenic properties of phorbol ester and a Ca2+ ionophore in bovine adrenocortical cell suspensions

When added independently to bovine adrenocortical fasciculata cell suspensions, 12 tetradecanoyl-phorbol-13 acetate (TPA) and the Ca2+ ionophore A23187 activated net cortisol production in a time and dose-dependent manner during one hour incubation. When added together (each at 1 microM concentration), the drugs appeared synergistic and mimicked the steroidogenic effect of suboptimal concentration of angiotensin II or acetylcholine on these cells, with no detectable variation of cellular cyclic nucleotide levels. In addition, the drug mixture markedly enhanced the steroidogenic effect of acetylcholine. These observations suggest that Ca2+-activated, phospholipid dependent protein kinase, which is present in adrenal cortex, might be considered as a possible target in the mechanism of action of steroidogenic agents such as angiotensin and acetylcholine, acting in adrenocortical cell through cyclic AMP independent processes.