Leu-enkephalin-like material in nerves and enterochromaffin cells in the gut. An immunohistochemical study.

The distribution and cellular localization of leu-enkephalin in the gut and pancreas was studied by immunohistochemistry using two different antisera, one specifically directed against leu-enkephalin and the other cross reacting with met-enkephalin. The results were identical with both antisera. In all species examined, enkephalin-immunoreactive material was found in nerves of the smooth muscle, particularly numerous in the myenteric plexus. Here, immunoreactive nerve cell bodies were observed occasionally. In addition, enkephalin-immunoreactive material was demonstrated in gut endocrine cells of chicken, mouse, rat, pig and monkey but not of guinea pig, cat and man. Enkephalin cells were detected also in the exocrine parenchyma of the porcine pancreas. They were rare in the gut of mouse, rat and monkey but numerous in the antrum and duodenum of pig where they were identified as 5-hydroxytryptamine-storing enterochromaffin cells. The enkephalin-containing cells of the porcine antrum and duodenum were defined ultrastructurally by the consecutive semithin/ultrathin section technique. The ultrastructural features were typical of enterochromaffin cells, the most characteristic ones being the irregular shape and high electron density of the cytoplasmic granules. The immunoreactive material was confined to the cytoplasmic granules.