Specific binding of Leu-enkephalin to small and large intestinal epithelial cells from guinea-pig

Leu-enkephalin receptors were identified in guinea-pig intestinal mucosa in small as well as in large epithelial cells. Binding studies at apparent equilibrium could be interpreted in terms of two populations of receptors in every intestinal segment. Leu-enkephalin receptors were unequally distributed along the intestinal mucosa, with the lowest density but the highest affinity values in the caecum and colon. Duodenal epithelial cells exhibited the highest binding values due to a great number of low-affinity receptors. Receptors exhibited a high degree of specificity for Leu-enkephalin as evidenced by the poor competition shown by a variety of enkephalin analogues and naloxone and the lack of effect of other unrelated peptides present in the intestinal tract.