PITUITARY ADENYLATE-CYCLASE ACTIVATING POLYPEPTIDE (PACAP) AND ITS RECEPTORS - NEUROENDOCRINE AND ENDOCRINE INTERACTION

The recent progress of research on the functions of pituitary adenylat e cyclase activating polypeptide (PACAP), especially endocrine and neu roendocrine interactions, is described. Studies of the genes encoding the PACAP precursor and the type I PACAP receptor provide information on the control of PACAP gene expression and on the relationship betwee n the structure of the receptor subtypes and the activation of various signal transduction pathways. The availability of specific antisera a gainst PACAP and the type I PACAP receptor made it possible to examine their distributions in the brain and other tissues. Immunohistochemic al studies and physiological studies with synthetic PACAP indicate tha t PACAP is a new type of hypophysiotropic hormone and also functions a s a neurotransmitter, neuromodulator, and neurotrophic factor in the c entral nervous system. The abundance of PACAP and its type I receptors in the adrenal medulla and the results of studies with synthetic PACA P suggest that PACAP is a potent noncholinergic secretogue for catecho lamines. PACAP and its receptors are also present in the pancreas and appear to play a regulatory role in insulin secretion at extremely low concentrations in a glucose-dependent manner. Immunohistochemical dem onstration of PACAP and its receptors in the testicular spermatids at early stages suggests an important role of testicular PACAP in spermio genesis. Together with its actions on pituitary gonadotropes, this sug gests that it plays a key role in reproduction. (C) 1995 Academic Pres s, Inc.