A dual pathway for ACTH steroidogenic action in purified adrenocortical cells.

Isolated adrenal fasciculata cells were purified by centrifugation through a 0-50% hyperbolic gradient of PercollR. The dose-dependence and kinetics of both intracellular cyclic AMP accumulation and steroidogenesis in response to ACTH1-39 and ACTH5-24 (corticotropin-(1-39) and corticotropin-(5-24)-peptides) were determined using purified cells. The rate of intracellular cyclic AMP formation was maximal during the first five minutes after hormone addition and remained constant or fell thereafter. Therefore intracellular cyclic AMP accumulation, assessed after 5 min., was compared with steroid output after 20 min. Maximal steroidogenesis was elicited by ACTH5-24 without discerning a significant stimulation of intracellular cyclic AMP accumulation. ACTH6-24 (corticotropin-(6-24)-peptide) could completely inhibit the intracellular cyclic AMP accumulation elicited by ACTH1-39 or by ACTH5-24 at concentrations that only partially inhibited steroidogenesis. It is possible that there are two pathways for the steroidogenic action of ACTH, one of which is obligatorily mediated by intracellular cyclic AMP, and another which involves a different mediator.