EFFECTS OF PITUITARY ADENYLATE-CYCLASE ACTIVATING PEPTIDE (PACAP) ON THE RAT ADRENAL SECRETORY ACTIVITY - PRELIMINARY IN-VITRO STUDIES

PACAP did not affect secretory activity of dispersed rat adrenocortica l cells, but it markedly raised aldosterone (ALDO) and corticosterone (B) production by adrenal slices, containing both medullary and cortic al tissues. The secretagogue effects of PACAP were suppressed by PACAP (6-38). a specific competitive antagonist. Isoprenaline (IF) enhanced ALDO, but not B secretion of adrenal slices, and I-alprenoloI (AL) com pletely blocked IP effect. AL and corticotropin-inhibiting peptide (CI P) partially reversed ALDO response to a maximal effective concentrati on of PACAP; AL did not affect B response to a maximal effective conce ntration of PACAP, while CIP completely annulled it. Quarters of regen erated adrenocortical autotransplants, that are completely deprived of chromaffin cells, though displaying ALDO and B responses to IP and AC TH, were insensitive to PACAP. The hypothesis is advanced that adrenal medulla plays a pivotal role in the mechanism(s) underlying the adren ocortical secretagogue action of PACAP. being mineralocorticoid and gl ucocorticoid responses probably mediated by the release by chromaffin cells of catecholamine and ACTH or exclusively ACTH, respectively.