Motilin receptors (provisional nomenclature) are activated by a 22 amino-acid peptide derived from a precursor (MLN, P12872), which may also generate a motilin-associated peptide (MLN, P12872). These receptors are also suggested to be responsible for the gastrointestinal prokinetic effects of certain macrolide antibiotics (often called motilides; e.g. erythromycin), although for many of these molecules the evidence is sparse.

In laboratory rodents, the gene encoding the motilin percursor appears to be absent, while the receptor appears to be a pseudogene [7,18]. Functions of motilin (MLN, P12872) are not usually detected in rodents, although brain and other responses to motilin and the macrolide alemcinal have been reported and the mechanism of these actions are obscure [14,16]. Marked differences in ligand affinities for the motilin receptor in dogs and humans may be explained by significant differences in receptor structure [19]. Note that for the complex macrolide structures, selectivity of action has often not been rigorously examined and other actions are possible (e.g. P2X inhibition by erythromycin; [25]). Small molecule motilin receptor agonists are now described [10,20,24]. The motilin receptor does not appear to have constitutive activity [8]. Although not proven, the existence of biased agonism at the receptor has been suggested [13,15,17]. A truncated 5-transmembrane structure has been identified but this is without activity when transfected into a host cell [5].

* Key recommended reading is highlighted with an asterisk

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* Foord SM, Bonner TI, Neubig RR, Rosser EM, Pin JP, Davenport AP, Spedding M, Harmar AJ. (2005) International Union of Pharmacology. XLVI. G protein-coupled receptor list. Pharmacol Rev, 57: 279-288. [PMID:15914470]

Sanger GJ. (2008) Motilin, ghrelin and related neuropeptides as targets for the treatment of GI diseases. Drug Discov. Today, 13 (5-6): 234-9. [PMID:18342799]

* Sanger GJ, Wang Y, Hobson A, Broad J. (2012) Motilin: Toward a new understanding of the gastrointestinal neuropharmacology and therapeutic use of motilin receptor agonists. Br. J. Pharmacol.,  [Epub ahead of print]. [PMID:23189978]

* Takeshita E, Matsuura B, Dong M, Miller LJ, Matsui H, Onji M. (2006) Molecular characterization and distribution of motilin family receptors in the human gastrointestinal tract. J Gastroenterol, 41: 223-230. [PMID:16699856]

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Anthony P. Davenport Clinical Pharmacology Unit University of Cambridge Level 6, Centre for Clinical Investigation Box 110, Addenbrooke's Hospital Cambridge, CB2 2QQ UK