Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates cyclic AMP formation as well as peptide output of cultured pituitary melanotrophs and AtT-20 corticotrophs.

The present study was aimed at investigating whether PACAP stimulates accumulation of cAMP, as well as hormonal secretion of homogeneous populations of pituitary proopiomelanocortin (POMC) cells, namely melanotrophs and AtT-20 corticotrophs. PACAP was shown to enhance cAMP accumulation in a dose-dependent fashion in both cell types (with EC50 values of approx. 10(-10) M) and elicited additive increases of cAMP production with CRF in melanotrophs, but not in corticotrophs. PACAP also stimulated dose-dependently the secretion of alpha-MSH and ACTH, with EC50 concentrations of about 10(-9) M. In melanotrophs, bromocriptine significantly depressed PACAP-induced cAMP formation and blunted by more than 90% stimulated alpha-MSH release. This study shows that (1) pituitary POMC cells did respond to PACAP by enhancing cAMP accumulation and elevating hormone secretion as well; (2) the effect of PACAP was additive with CRF on cAMP production in melanotrophs, but not in corticotrophs, while there was no additivity on peptide output from both cell types; (3) activation of dopamine receptors in melanotrophs dampened both cAMP formation and peptide secretion. These findings are consistent with PACAP playing a possible hypophysiotropic role in the regulation of pituitary POMC cell activity.