Background & aims: Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates protein and/or amylase secretion from isolated rat pancreatic acini. The effect of PACAP on pancreatic secretion in vivo and its mechanism of action were studied.
Methods: Rats were prepared with pancreatic duct cannulation, pyloric ligation, and bile diversion into duodenum, and 2.5, 5, and 10 nmol/kg PACAP-27 was administered intravenously while pancreatic juice was collected for 30 minutes. In other groups of rats, the effect of 10 nmol/kg PACAP-27 was studied under the influence of either atropine; loxiglumide, an antisecretin serum; a combination of both loxiglumide and the antiserum; or a PACAP antagonist (PACAP 6-38). Plasma secretin and cholecystokinin concentrations were measured by radioimmunoassay.
Results: (1) PACAP dose-dependently increased pancreatic secretion of fluid, bicarbonate, and protein; (2) the increase in pancreatic secretion paralleled that of plasma secretin and cholecystokinin; (3) a combination of loxiglumide and antisecretin serum eliminated the PACAP-stimulated pancreatic secretion, whereas loxiglumide or antisecretin serum alone partially but significantly blocked pancreatic secretion; (4) atropine failed to influence PACAP-induced pancreatic secretion; and (5) PACAP antagonist profoundly suppressed the PACAP action.
Conclusions: PACAP-27 dose-dependently stimulates pancreatic secretion of fluid, bicarbonate, and protein in rats. This effect is mediated by release of both secretin and cholecystokinin and is independent of cholinergic tone.