Transient periovulatory expression of pituitary adenylate cyclase activating peptide in rat ovarian cells

Pituitary adenylate cyclase activating polypeptide (PACAP), a potent stimulator of cAMP formation, has a widespread distribution in neuronal elements of the central nervous system and a number of peripheral organs. Recently, PACAP has also been shown to be stage specifically expressed in the spermatogenic cells from the rat testis. This prompted us to examine the cell-specific expression of PACAP during the estrous cycle in the rat ovary by in situ hybridization with a digoxiginin UTP-labeled RNA probe and by immunohistochemistry using a specific monoclonal antibody. Ovaries from PMS gonadotropin (PMSG)/human CG (hCG) treated immature animals were examined 0, 12, 24, 48, 54, 57, 58.5, 60, 61.5, 63, 66, 72, and 96 h after PMSG treatment. Ovaries from adult cyclic rats were examined at 1000 h on each day of the estrous cycle and at 0400 h on estrus morning. PACAP positive cells were observed in the preovulatory and ovulatory period, i.e. 6-18 h following hCG injection in the PMSG induced cycle and at 0400 h and 1000 h on estrus morning in adult cyclic animals. Both PACAP messenger RNA (mRNA) and PACAP immunoreactivity were observed in the majority of granulosa and cumulus cells from large preovulatory follicles, in the majority of the cells comprising the interstitial glandular tissue and in solitary theca cells of growing and mature follicles. In PMSG/hCG treated animals, positive signals were also observed in solitary theca and interstitial cells 12 h after PMSG injection. PACAP immunoreactive nerve fibers were observed in all ovaries examined, located in the interstitial glandular tissue or in the loose connective tissue. Northern blotting of ovarian tissue confirmed the transient preovulatory and ovulatory expression of PACAP. Three transcripts were observed. The most predominant band had a size of approximately 1.2 kilobase pairs, corresponding to the transcript observed in the testis. Two bands of 2.4 and 3.0 kilobase pairs, corresponding to the transcripts from neural tissue, were also observed. The complex distribution of PACAP positive cells and nerve fibers suggests that the peptide could be a local regulator of a number of the events that take place in the periovulatory period as well as during early folliculogenesis in the ovary.