Effect of methionine-enkephalin and naloxone on bombesin-stimulated gastric acid secretion, gastrin, and pancreatic polypeptide release in the dog.

In four dogs with chronic gastric fistulae, bombesin infusion was used to stimulate the release of gastrin and pancreatic polypeptide (PP) as well as rates of gastric acid secretion. Neither methionine-enkephalin (met-enkephalin) nor naloxone alone or the combination of these agents altered bombesin-stimulated gastrin release. met-enkephalin alone (but not naloxone) significantly inhibited the gastric secretory response to bombesin, but this inhibitory effect was not influenced by the simultaneous infusion of naloxone; the data suggested that the effect of met-enkephalin was indirect, and perhaps modulated by another inhibitory mechanism. Whereas PP release induced by bombesin was not affected by naloxone, it was significantly suppressed by met-enkaphalin; since this inhibition was virtually totally reversed by naloxone, the data suggested that the effect of opiate peptides on the release of pancreatic polypeptide was direct and mediated by a specific opiate receptor.