COMPARATIVE-STUDY OF VASCULAR RELAXATION AND RECEPTOR-BINDING BY PACAP AND VIP

The pharmacological properties of the pituitary adenylate cyclase acti vating peptides (PACAPs) and vasoactive intestinal peptide (VIP) were compared using (i) relaxation of vascular and gastric smooth muscle in vitro, and (ii) radioligand binding to membrane preparations of a var iety of tissues. Vasoactive intestinal peptide and PACAP-27 were simil arly potent in relaxing rat mesenteric arteries, porcine coronary arte ries, and rat gastric smooth muscle, whereas PACAP-38 was either more or less potent than the other two peptides depending on the tissue mod el. Cross-desensitization to relaxation and radioligand binding studie s of porcine coronary arteries suggested that VIP and the PACAPs inter act with a common receptor in this tissue. A PACAP-preferring receptor with low affinity for VIP was identified in radioligand binding studi es of rat brain and anterior pituitary. A second, nonselective, recept or that binds VIP and both PACAPs with high affinity was observed in p reparations of rat and porcine arteries and rat lung, liver, brain, an d anterior pituitary.