Modulation of post-prandial insulin release by ingested opiate-like substances in dogs

We have previously demonstrated that opiate-like substances in food protein (exorphins), contained in the peptic digest of gluten, stimulate insulin and glucagon release in dogs and that this effect is inhibited by the opiate antagonist naloxone. The present study was designed to evaluate the possible rôle of ingested opiate-like substances in the modulation of post-prandial insulin release. Similarly, the addition of synthetic β-casomorphins, which are the opioid-active material of bovine casein peptone, elicit a stimulation of post-prandial insulin release during a liver extract-sucrose test meal. The addition of met-enkephalin to a liver extract-sucrose test meal also augmented the post-prandial insulin response. Both stimulatory effects were reversed by oral naloxone, as was the post-prandial increase of insulin following ingestion of bovine casein peptone (casopeptone). The post-prandial insulin response to digested and undigested liver extract was not affected by naloxone, suggesting that the foregoing effects are likely to be specific to opiate-like materials contained in foodstuff (exorphins). In view of previous findings, the present data are compatible with a role of opiate-like substances contained in ingested nutrients in the regulation of post-prandial insulin secretion.