Central Effects of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) on Gastric Motility and Emptying in Rats

Pituitary adenylate cyclase activatingpolypeptide (PACAP) is a new member of thesecretinglucagon-vasoactive intestinal peptide (VIP)peptide family. PACAP is widely distributed not only inthe mammalian brain but also in the gastrointestinal tract.Here, we investigated the effects of central andperipheral administrations of PACAP on gastric motilityand gastric emptying in rats. We found that theintracerebroventricular or intracisternal injection of PACAP increasedgastric motility in a dose-dependent manner. Theintracisternal injection of PACAP delayed gastricemptying. These central effects of PACAP on gastricmotility and emptying were blocked by bilateralvagotomy. In contrast, intravenous administration ofPACAP decreased gastric motility and delayed gastricemptying. The peripheral inhibitory effect wasunaffected by bilateral vagotomy, adrenalectomy,phentolamine, and propranolol. We investigated theeffect of PACAP38 on blood glucose levels (BGL) at thesame doses as those used in the gastric motility andemptying studies in urethane-anesthetized rats. Theintravenous but not intracerebroventricular injection ofPACAP38 (1-8 nmol/rat) produced a significant increasein the BGL. We conclude that PACAP has opposite central and peripheral effects on gastricmotility, ie, central PACAP activates the vagal pathwayin the central nervous system to increase gastricmotility, whereas peripheral PACAP inhibits gastricmotility via an unknown pathway. The delay in gastricemptying after the central administration of PACAP mightbe due to the lack of coordinated gastropyloroduodenalcontraction, whereas that after the peripheral administration might be due to the inhibitionof gastric contraction, and this effect may be relatedto the hyperglycemic action of PACAP.