Gonadotropin stimulation of pituitary adenylate cyclase-activating polypeptide (PACAP) messenger ribonucleic acid in the rat ovary and the role of PACAP as a follicle survival factor.

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel neuropeptide with considerable homology to vasoactive intestinal peptide and GH-releasing hormone, exists in two biologically active forms, PACAP-38 and -27. The presence of PACAP in the ovary has been demonstrated, where it stimulates steroidogenesis and cAMP accumulation in cultured granulosa cells. In the present study, gonadotropin regulation of PACAP gene expression was examined in PMSG/human (h)CG-treated immature rat ovaries and cultured preovulatory follicles. Northern blot analysis of ovaries obtained from PMSG/hCG-treated immature animals revealed the transient induction of PACAP transcripts by hCG, reaching a maximum at 6 h. The major cell types expressing PACAP messenger RNA were granulosa cells of preovulatory follicles and some theca/interstitial cells. In preovulatory follicles cultured in serum-free medium, PACAP transcripts were transiently induced by LH and FSH, reaching a maximum 6-9 h after stimulation in granulosa cells but not in theca cells. Treatment with cycloheximide or alpha-amanitin abolished LH-induced PACAP transcripts, indicating that new protein synthesis and transcription are necessary. Treatment with MDL-12,330A, an inhibitor of adenylate cyclase, inhibited LH-induced PACAP messenger RNA, and forskolin mimicked the LH action, implying the role of adenylate cyclase activation. In contrast, treatment with chelerythrine, an inhibitor of protein kinase C, and 2-O-tetradecanol-phorbol-13-acetate had no effect. We further tested the role of PACAP in follicle apoptosis using apoptotic DNA fragmentation analysis. Treatment with PACAP-38 suppressed follicle apoptosis in a dose-dependent manner. Moreover, the LH suppression of follicle apoptosis was partially blocked by cotreatment with PACAP-38 antagonist, indicating mediation by endogenous PACAP-38. These results suggest that PACAP, transiently induced by the gonadotropin surge, could be a local regulator of a number of events and may act as a follicle survival factor during the periovulatory period.