Candidate GI Hormone: Motilin
Motilin is a 22-amino acid peptide found primarily in the duodenum, with lesser amounts occurring in the more distal portions of the small bowel. Its circulating half-life is about 4.5 minutes, and the kidney appears to play an important role in its catabolism. The physiologic stimuli for its release are not known. Its proposed physiologic action is to initiate the migrating motor complex (MMC). MMC is a wave of intense propulsive motor activity that sweeps the length of the gut, from stomach to ileocecal junction, at about 90-minute intervals during the interdigestive (fasting) phase of GI activity. Plasma motilin is low during the digestive (fed) phase, but its concentration varies cyclically during the interdigestive phase and its peak concentration coincides with the initiation of the MMC in the stomach.