Pituitary adenylate cyclase-activating peptide stimulates acute progesterone production in rat granulosa/lutein cells via two receptor subtypes

Pituitary adenylate cyclase-activating peptide (PACAP) is transiently expre ssed in ovarian granulosa/lutein cells from eCG/hCG-treated rats, and in vi tro immunoneutralization of endogenously released PACAP inhibits acute prog esterone secretion and subsequent luteinization in such cells. This suggest s that PACAP mediates locally some of the effects of the LH surge, but the putative PACAP receptor(s) involved in such an auto or paracrine activity i s presently unknown. Reverse-transcription polymerase chain reaction with s pecific primers to the three cloned PACAP-binding receptors called PAC(1), VPAC(1), and VPAC(2) demonstrated both PAC(1) and VPAC(2) mRNA in extracts from preovulatory follicular cells. Radioligand-binding assays revealed the presence of high-affinity binding sites with characteristics of these two receptors on the intact cells, and autoradiography demonstrated that the bi nding was restricted to a minor proportion of the follicular cells as well as the oocytes. Pituitary adenylate cyclase-activating peptide and vasoacti ve intestinal peptide (VIP) dose-dependently stimulated cAMP accumulation a nd acute progesterone accumulation. Forskolin and db-cAMP also stimulated a cute progesterone accumulation, and the protein kinase A inhibitor H89 dose -dependently inhibited peptide induced acute progesterone accumulation, sug gesting involvement of cAMP and the protein kinase A pathway in the process . In conclusion, two of the three PACAP binding receptors are present on pr eovulatory follicular cells and are involved in the effects of PACAP on acu te progesterone production. The data provide further evidence to establish PACAP as an auto- or paracrine regulator of LH-induced acute progesterone p roduction in rat preovulatory follicles.