Effect of bombesin and related peptides on the release and action of intestinal hormones on pancreatic secretion.

1. Pancreatic volume flow as well as bicarbonate and protein secretion from pancreatic fistulas have been measured in response to i.v. infusion of graded doses of bombesin and related peptides containing the COOH-terminal fragment of the bombesin molecule in conscious dogs with intact antrum and in anaesthetized animals with antrectomy, or antrectomy and enterectomy. 2. Bombesin and related peptides given to conscious dogs produced a potent and dose-dependent increase in pancreatic protein output reaching a maximum equal to that induced by the octapeptide of cholecystokinin (OP-CCK) as well as a small rise in bicarbonate output attaining a peak amounting to about 10% of that evoked by secretin. The serum gastrin level rose progressively during the infusion of bombesin to reach a peak with the highest dose of peptide. 3. Bombesin infused i.v. in anaesthetized animals with resected antrum also evoked a marked increase in pancreatic protein secretion without significant changes in the serum gastrin level. Following the removal of the antrum and small intestine, bombesin failed to show any stimulation of the pancreatic secretion or any change in the serum gastrin level. It is concluded that the strong stimulatory action of bombesin and related peptides on pancreatic secretion cannot be entirely ascribed to the release of gastrin but might be attributed at least in part to the release of intestinal hormones, particularly CCK. 4. Atropine and the growth hormone-release inhibiting hormone (GH-RIH), which were shown to inhibit the release of CCK induced by duodenal perfusion of an amino acid mixture, also caused the inhibition of pancreatic protein secretion by bombesin but failed to affect the pancreatic response to OP-CCK. The results indicate that bombesin releases, in addition to gastrin, CCK from the gut by a mechanism largely dependent upon cholingeric innervation.