PACAP acts through VIP type 2 receptors in the rat testis

Pituitary adenylate cyclase-activating peptide (PACAP) is present and synthesized in the testis in large amounts. Messenger RNA encoding the peptide is expressed in a stage specific manner in the developing germ cells. PACAP regulates a variety of physiological actions, among them, paracrine modulation of spermatogenesis. The PACAP peptides are potential ligands of at least three receptor types, the type I PACAP receptor, VIP1 and VIP2 receptors. Although PACAP27 binding sites have found in the testis, the receptor at which it acts has not been identified. We used in situ hybridization with riboprobes to identify the PACAP binding receptor present in the testis. Neither type I PACAP receptor, nor VIP1 receptor mRNA was present within the germ cells. Using the VIP2 receptor probe there was strong labelling within some cross sections of the seminiferous tubuli, while others were not labelled. The in situ results were also confirmed using reverse-transcription PCR (RT-PCR). Our data suggest that PACAP mediates its possible paracrine effect in the testis through the VIP2 receptor.