Vasoactive intestinal polypeptide in vagally mediated pancreatic secretion of fluid and HCO3

The role of nerves that liberate vasoactive intestinal polypeptide (VIP) in the porcine pancrease as mediators of the atropine-resistant action of the vagus on flow and bicarbonate (HCO3) secretion was examined. Efferent electrical stimulation of the vagus in atropinized pigs produced a profuse flow of pancreatic juice with high HCO3 content concomitantly with a significant increase in pancreatic VIP output from 13 to 113 fmol/min. Intravenous administration of somatostatin (SRIF) during continuous electrical vagal stimulation caused a parallel suppression of the VIP release and the pancreatic fluid and HCO3 secretion to prestimulatory values. The SRIF-induced reduction in fluid and HCO3 secretion seemed to be mediated via an inhibition of the VIP release rather than through a direct effect on the exocrine cells, inasmuch as SRIF did not influence the VIP-provoked exocrine response from the in vitro isolated perfused porcine pancreas. The results support the view that VIP is transmitter in the vagally induced atropine-resistant water and HCO3 secretion from the porcine pancreas.