Molecular forms of motilin in the mammalian and human gut and human plasma.
Regional specific antibodies and gel permeation chromatography were used to analyze the molecular forms of motilin in the human gut and plasma and in the porcine gut. The same antibodies were also used for immunocytochemical localization of the cell of origin of motilin. Two main molecular forms of motilin were identified, peak I eluting at a volume suggesting a larger molecular weight substance (Kav = 0.16) and peak II coeluting with the porcine motilin standard (Kav = 0.67). Peak I accounted for over 50% of the total motilin immunoreactivity in the human gut, whereas in the porcine intestine it represented less than 5%. Peak I thus appeared to have a greater N-terminal sequence similarity with the porcine motilin standard. Chromatographic analysis of human plasma showed the presence of both immunoreactive peaks in approximately equal amounts which were both suppressed following infusion of somatostatin. Infusion of porcine motilin resulted in the expected rise of plasma immunoreactivity in the peak II position, whereas peak I was significantly depressed, suggesting the possibility of a negative feedback. Immunocytochemistry revealed that both antibodies immunostained equally the non argentaffin cell, which contained small round, electron-dense granules. In addition some argentaffin enterochromaffin cells were stained predominantly with the N-terminal specific antibody.