Enkephalin: the latest instalment

Beta-endorphin in the human gallbladder

The presence of beta-endorphin-like immunoreactivity (beta-END-LI) in human gallbladder and its release were examined by means of radioimmunochemical measurements and immunohistochemical stainings. beta-END-LI was detected in the gallbladder (27.2 +/- 3.2 ng/g wet weight, mean +/- S.E.). The immunoreactivity in beta-END-LI extracted from the gallbladder was similar to that of synthetic beta-END, judging from the result of its inhibition curve parallel to that of the synthetic substance in the radioimmunoassay (RIA) system. On gel-filtration chromatography of a gallbladder extract, two components of beta-END-LI were found; one eluted on a position of beta-lipotropin (beta-LPH) and another on a position of synthetic beta-END. Specific beta-END-LI positive cells were detectable in metaplastic mucous glands. When human gallbladder mucosa was perfused with a solution of 10(-8) M or 10(-6) M cholecystokinin octapeptide (CCK-8), the release of beta-END-LI from mucosa into the perfusate increased 2-3 fold. These results indicate that beta-END-LI present in human gallbladder is released by the direct action of CCK-8 on the gallbladder mucosa and suggest that it may have a physiological or pathophysiological role.

Inhibitory effect of enkephalins on contractions of the guinea-pig ileum elicited by PGE1

Methionine-enkephalin and leucine-enkephalin (m-enk and 1-enk) as well as D-Ala2-methionine-enkephalin amide have been shown to antagonize contractions of the isolated guinea-pig intestine elicited by PGE1, the last mentioned being the most potent of the three. The inhibitory effect of these pentapeptides is abolished by naloxone.

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.