Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.