Neuromediated action of beta-casomorphins on ion transport in rabbit ileum.

beta-casomorphins (beta-CMs) are opioid peptides derived from milk beta-casein. The beta-casomorphin analog beta-[DAla2,4, Tyr5] CM-5-NH2 reduced short-circuit current (lsc) and stimulated electrolyte absorption by an opioid effect in rabbit ileum in vitro. This effect was inhibited by 10(-7) M tetrodotoxin, 10(-6) M epinephrine and 10(-5) M naloxone. Atropine in the 10(-7)-10(-5) M range and 10(-5) M hexamethonium did not inhibit the action of the peptide on lsc. In comparison the muscarinic effect of 10(-3) M carbachol was inhibited by atropine in the 10(-8)-10(-5) M range. These results indicate that the action of the beta-casomorphin analog was neuromediated and suggest that this peptide acted on the submucosal plexus located on the blood side of the intestinal epithelium. A physiological role of the food-derived beta-CMs peptides implies the passage of the active sequences from the lumen to the blood side of the intestine.