Intramural distribution of Met5-enkephalin-Arg6-Gly7-Leu8 in sphincter regions of the human gut

The intramural distribution of Met5-enkephalin-Arg6-Gly7-Leu8 (MERGL) was studied in the oesophago-cardiac, pyloric, ileo-caecal and sigmoid-recto-anal regions of the human digestive tract. Serial samples encompassing each area were separated into mucosa, submucosa and muscularis externa and extracted for radioimmunoassay. Comparatively low levels of MERGL immunoreactivity were measured throughout the cardiac junction. Conversely, a remarkable peak of MERGL concentration was detected at the pyloric junction, in both submucosa and muscularis. A progressive decrease in tissue levels of the same peptide, most evident in the submucosa, was detected on the proximal side of the ileo-caecal region. In the distal sigmoid colon and rectum MERGL concentrations showed a rapid decline, down to very low levels in the anal canal. The results may suggest the involvement of an enkephalinergic mechanism in the control of the human pylorus.