| Abstract: | Calcium is required for ACTH stimulated steroidogenesis in adrenal tumor cells in tissue culture. In the absence of calcium, the dose of ACTH required to induce half maximum steroidogenesis was increased 30 fold. In contrast to intact adrenal glands or isolated adrenal cells, high doses of ACTH (50 mU/ml) maximally stimulated steroidogenesis in the absence of calcium. Growth for up to six days in medium with low calcium did not affect basal or ACTH induced steroidogenesis. The addition of calcium to cells incubated with ACTH produced a maximum steroidogenic response in 15 minutes. In contrast to intact adrenal glands, calcium is not required for adenosine-3′,5′-cyclic monophosphate (cyclic AMP) stimulated steroidogenesis in adrenal tumor cells. These experiments support the concept that calcium is important at the level of ACTH-membrane receptor site interaction or activation of adenyl cyclase in adrenal tumor cells. |
