Possible involvement of vasoactive intestinal polypeptide in the central stimulating action of pituitary adenylate cyclase-activating polypeptide on prolactin secretion in the rat.

Effect of pituitary adenylate cyclase-activating polypeptide (PACAP) on prolactin (PRL) secretion was studied in Wistar strain male rats in vivo. Intravenous injection of PACAP-38 and PACAP-27 resulted in a dose-related increase in plasma PRL levels both in conscious rats and in urethane-anesthetized rats. In anesthetized animals, i.c.v. injection of PACAP-38 and PACAP-27 also elicited a dose-related increase in plasma PRL. The PRL secretion induced by i.c.v. injection of PACAP-38 was attenuated by pretreatment with rabbit antiserum to vasoactive intestinal polypeptide (VIP). These findings suggest that PACAPs stimulate PRL secretion in the rat by acting not only directly on the pituitary but also indirectly through the central nervous system, at least partly, via hypothalamic VIP.