Enkephalins in the inferior mesenteric ganglion of the cat and in the area of the lower digestive tract innervated by this ganglion: Quantification by radio-immunoassay and characterization by high pressure liquid chromatography

Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg-Gly-Leu were quantified and characterized in the cat inferior mesenteric ganglion and in the area of the lower digestive tract innervated by this ganglion, including the proximal colon, distal colon and internal anal sphincter. In the structures studied, the concentrations of enkephalins expressed as femtomole/mg of wet tissue ranged from 66 to 160 with Met-enkephalin, from 15 to 45 with Leu-enkephalin and from 2 to 12 for Met-enkephalin-arg-gly-leu. In the lower digestive tract, the Met- and Leu-enkephalin content decreased from the proximal colon to the internal anal sphincter. The Met-enkephalin versus Leu-enkephalin ratio of the structures investigated were as follows: inferior mesenteric ganglion 3.2, proximal colon 4.4, distal colon 5, internal and sphincter 4.5. In individual samples of all the structures assayed the results of high pressure liquid chromatography (HPLC) analysis pointed to the presence of authentic Met- and Leu-enkephalin. HPLC analysis could not be carried out on Met-enkephalin-Arg-Gly-Leu due to the very low concentrations of this peptide in all the structures assayed. Our results, combined with those of previous immunohistochemical and physiological studies, support the idea that enkephalins are involved in the nervous control of the motility of the lower digestive tract.