DOSE-RESPONSE EFFECTS OF VIP ON THE RABBIT EXOCRINE PANCREATIC-SECRETION - COMPARISON WITH PACAP-27 ACTIONS

A dose-response study of the effects of vasoactive intestinal peptide (VIP) on the exocrine pancreatic secretion of the rabbit has been made . Furthermore, the actions of VIP and pituitary adenylate cyclase acti vating peptide (PACAP) on the exocrine pancreatic secretion were compa red at a similar molar dose. After the infusion of VIP a linear dose-r esponse relationship for pancreatic flow rate and bicarbonate output, up to the dose of 4 mu g/kg, was observed. VIP acts as a partial agoni st of secretin, the rabbit pancreas being less sensitive to VIP compar ed with other mammals. Moreover, VIP did not significantly stimulate t he pancreatic protein output. PACAP stimulated the hydroelectrolyte fr action of the exocrine pancreatic secretion in a similar manner to tha t of VIP. Unlike what was observed with VIP, PACAP, on the same molar basis, significantly stimulated the protein and amylase outputs. Furth ermore, PACAP releases VIP, so that the action of PACAP on the hydroel ectrolyte fraction may be partially mediated by VIP; on the other hand , VIP is not involved in the effect of PACAP on the pancreatic enzyme secretion of this species.