Expression of pituitary adenylate cyclase activating polypeptide (PACAP) and PACAP type IA receptor mRNAs in granulosa cells of preovulatory follicles of the rat ovary

Pituitary adenylate cyclase activating polypeptide (PACAP) was isolated fro m ovine hypothalamus and known to stimulate the production of cAMP in anter ior pituitary cells. In the recent report, the expression of PACAP was dete cted in preovulatory follicles, and treatment with PACAP stimulated the pro duction of progesterone and prostaglandin E-2 through the action of AC and PLC pathways in the ovary. PACAP binds to three type receptors. Type I A re ceptor is coupled to adenylate cyclase (AC) and phospholipase C (PLC) pathw ays, while type I B and type II receptors are only coupled to AC. Thus, the present study aimed to evaluate the temporal expression of PACAP and its t ype I A receptor mRNAs in the rat ovary after treatment with pregnant mare' s serum gonadotropin and human chorionic gonadotropin (hCG). Northern blot analysis showed that PACAP transcripts were transiently expre ssed from 3-9 hr after hCG treatment, reaching a maximum at 6 hr. During th ese time points, PACAP mRNAs were specifically and strongly expressed in gr anulosa cells and cumulus cells of large preovulatory follicles and interst itial glandular cells. Type I A receptor mRNAs were also transiently expres sed in granulosa cells of large preovulatory follicles from 3-9 hr after hC G treatment. PACAP and its type I A receptor mRNAs were expressed in the sa me preovulatory follicles. These results demonstrate that PACAP acts as an autoregulator or pararegulator through type I A receptor in granulosa cells and cumulus cells of large preovulatory follicles. Thus, we suggest that P ACAP may have a critical role in granulosa cells of preovulatory follicles for the preparation of ovulation. Mol. Reprod. Dev. 55:379-386, 2000. (C) 2 000 Wiley-Liss, Inc.