THE STIMULATORY EFFECTS AND BINDING CHARACTERISTICS OF PACAP27 IN RATDISPERSED PANCREATIC ACINI

Pituitary adenylate cyclase activating polypeptide (PACAP) is a recent ly isolated active peptide of the VIP (vasoactive intestinal peptide) family. Two bioactive forms, PACAP38 and PACAP27, a shorter N-terminal . amidated peptide of PACAP38, have been identified. In this study, we explored the action of PACAP27 in rat dispersed pancreatic acini and the characteristics of its binding sites. PACAP27 stimulated amylase s ecretion and intracellular cAMP production in a dose-dependent manner. Adding 0.5 mM IBMX increased the potency of PACAP27 on the amylase se cretion, but did not change the efficacy. The biological action of PAC AP27 was mediated via intracellular cAMP as is also the case with PACA P38 or VIP, The time course study, however, revealed that PACAP stimul ated the initial amylase secretion greater than VIP, suggesting an inv olvement of mechanisms other than intracellular cAMP. Binding studies using I-125-PACAP27 and I-125-VIP indicated that the binding sites for PACAP27 interacted with PACAP27 and VIP with a similar affinity. Thes e observations suggested the presence of type II PBCAP-binding sites i n the normal acini of the rat pancreas which may be functionally coupl ed with acinar enzyme secretion.