Motilin

Motilin is a polypeptide hormone secreted by Mo cells of the small intestine that increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin. Control of motilin secretion is largely unknown, although some studies suggest that an alkaline pH in the duodenum stimulates its release. Interestingly however, at low pH it inhibits gastric motor activity, whereas at high pH it has a stimulatory effect.

Apart from in humans, motilin receptors are found in pigs', rats' and cats' gastrointestinal tracts and in rabbits' central nervous systems.

Motilin agonists
Erythromycin and related antibiotics act as non-peptide motilin agonists, and are sometimes used for their ability to stimulate gastrointestinal motility. Administration of a low dose of erythromycin will induce peristalsis, which provides additional support for the conclusion that motilin secretion triggers this pattern of gastrointestinal motility, rather than results from it. However, some of erythromycin’s properties, including antibiotic activity, are not appropriate for a drug designed for chronic use over a patient's lifetime.

New motilin agonists are erythromycin based, however, it may be that this class of drugs becomes redundant; growth hormone secretagogue receptors share 52% of their DNA with motilin receptors and agonists of these receptors, termed ghrelins, can bring about similar effects to motilin agonists.