Expression of PACAP and its type-I receptor isoforms in the rat ovary

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the secretin/glucagon/vasoactive intestinal peptide (VIP)/growth hormone releasing hormone (GHRH) family of neuropeptides, several of which stimulate steroidogenesis in ovarian granulosa cells. PACAP receptors are of two major subtypes; the type I receptor (PACAP-I-R) has much higher affinity for PACAP than VIP, and the type II receptor (PACAP-II-R) has similar affinity for both peptides. In the rat ovary, expression of the PACAP gene was demonstrated by amplification of ovarian RNA by the reverse transcription/polymerase chain reaction (RT-PCR). In addition, hybridization of Northern blots of rat ovarian poly(A)+ RNA with a 706-nt rat hypothalamic PACAP-I-R cDNA probe revealed the presence of a 7.0 kb PACAP receptor transcript, similar to that detected in brain and hypothalamus. RT-PCR using specific primers for the PACAP-I-R gene yielded products of the expected size with RNA obtained from ovarian tissue, brain, and hypothalamus. The authenticity of the PCR products was confirmed by Southern blotting and nested PCR, which revealed at least three splice variants of the PACAP-I-R in the rat ovary. These findings demonstrate that both PACAP and PACAP-I-R isoforms are expressed in the rat ovary, where they could exert autocrine or paracrine actions on granulosa cell function.