Enkephalin-like immunoreactivity in the human gastrointestinal tract.

Morphine has powerful actions on brain and gut. Peptides with opiate-like actions (endorphins, enkephalins) are known to be normal constituents of the brain and now enkephalin-like immunoreactivity has been shown in the gut. Enkephalin-like immunoreactivity was present in all areas of the gut with particularly high concentration in the antrum and significant amounts in the upper small intestine. Immunocytochemistry on 1 micronm serial sections revealed enkephalin-like immunoreactivity in numerous cells of the antral mucosa, in a few cells of the duodenal mucosa and pancreas, and in the myenteric plexus of the gallbladder, cystic ducts, bileduct, and other areas of the lower intestine. Gastrointestinal physiology appears to be partly regulated by locally acting hormones and enkephalin may be one of these. The established effects of morphine on the alimentary tract provide a clue to the possible physiological role of enkephalin.