Actions of motilin on gastrointestinal motility and plasma immunoreactive motilin concentration in interdigestive and postprandial states.

Among biological actions of motilin on gastrointestinal motility, its action to induce phase III, activity front, of interdigestive myoelectric complex (IMC) appears to be of physiological significance. Synthetic motilin in a dose as little as 0.06 microgram/kg-h was shown to induce phase III in dog. A cyclic increase in fasting plasma immunoreactive motilin concentration (PIMC) occurred in phase III in dog and in a later part of phase II in man, suggesting strongly that there is an intimate relationship between cyclic increase in fasting PIMC and IMC. The observation also suggested that gastric acid secretion increases in phase II and phase III of IMC. The cyclic increase in the acid secretion may be related to a coincidental cyclic increase in PIMC. Ingestion of a meat meal results in a significant decrease in PIMC and abolishes the cyclic increase in PIMC, while IMC changes to digestive pattern after a meal. The significant decrease in PIMC is not attributed to the 3 known gut hormones including gastrin, octapeptide of CCK and secretin.