Motilin is a unique gut peptide. It is a twenty-two amino-acid peptide secreted by M¡ cells of the duodenal and jejunal mucosa. It increases the contractility of gastrointestinal smooth muscle, accelerating gastric emptying and colonic transit. There is a high basal motilin output that sets the background muscle tone (with peaks in secretion coinciding with initiation of the myoelectric complex) and which causes interdigestive muscle contraction.
Macrolide antibiotics such as erythromycin are motilin-receptor agonists, which explains the side effects of diarrhoea and abdominal cramps that are seen with use of such agents.
