Motilin: Physiology and What Research Reports
Motilin is a peptide hormone linked to the gastrointestinal tract and studied mainly for its relationship to gut motility. Published work has mapped where motilin and its receptor appear in humans and animals, described the receptor structure that also recognises erythromycin, measured motilin fluctuations in healthy volunteers by mass spectrometry, and examined motilin in settings such as childhood functional constipation and lactation. This page summarises what those studies reported. It is educational only and does not describe any protocol or product.
What Motilin Is
Motilin is a peptide hormone most often discussed in the context of the gastrointestinal tract. A 2021 comparative review in Frontiers in Endocrinology summarised motilin's structure, tissue distribution, receptors and relationship to gastrointestinal motility across a range of species (PMID 34497583). Researchers have also examined motilin alongside ghrelin: a 2019 study in human motilin receptor transgenic mice compared the effects of motilin receptor agonists and ghrelin in the same model system (PMID 30934667).
For readers who encounter "motilin" in a peptide context, it is useful to note that the term is used for three related things in the literature: the endogenous hormone itself, the motilin receptor (a G protein-coupled receptor), and synthetic or pharmacological agonists at that receptor, which were the subject of the 2019 transgenic mouse study (PMID 30934667). This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about health, symptoms or treatment.
Where Motilin Is Produced and Where Its Receptor Appears
Distribution work has been done in several species. The 2021 comparative review described motilin's tissue distribution and its receptor expression patterns as part of a cross-species overview of the peptide (PMID 34497583). In dogs, a 2015 study in Gastroenterology Research and Practice reported differential expression of the motilin receptor across different parts of the gastrointestinal tract (PMID 25918525), which is the kind of regional mapping that helps explain why responses differ between stomach and intestine.
Motilin has also been detected outside the gut lumen. A 2004 study in the Journal of Gastroenterology and Hepatology reported motilin in human milk together with elevated plasma motilin concentrations in lactating women (PMID 15377298). In the nervous system, a 2023 rat study reported that motilin and its receptor were expressed in the spinal dorsal horn in a model of acute incisional pain, and that intrathecal motilin injection alleviated pain behaviours in that model (PMID 36816129).
The Motilin Receptor and Why Erythromycin Comes Up
A 2023 paper in Science Advances described the structural basis for recognition of both motilin and erythromycin by the motilin receptor (PMID 36921049). That structural work is frequently cited because it addresses at a molecular level why a macrolide antibiotic and a peptide hormone can both engage the same receptor. In parallel, the 2019 transgenic mouse study examined motilin receptor agonists and ghrelin in animals carrying the human motilin receptor, an approach used because receptor pharmacology differs between species (PMID 30934667).
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Analytical approaches in the verified literature include mass spectrometry and immunological or molecular methods, depending on the question. A 2024 study in Frontiers in Endocrinology determined motilin fluctuations in healthy volunteers using liquid chromatography mass spectrometry (PMID 38544692). Clinical association studies have instead used serum measurements combined with genetics: a paper published in Minerva Pediatrics examined serum motilin levels together with motilin gene polymorphisms in children with functional constipation (PMID 27706119).
Molecular identification and functional testing in non-mammalian species make up a large share of motilin research. Researchers cloned motilin and investigated the mechanism of motilin-induced gastrointestinal motility in Japanese quail (PMID 27179882), characterised pheasant motilin along with its distribution and gastrointestinal contractility-stimulating action in the pheasant (PMID 34506789), identified motilin in the Japanese fire bellied newt (PMID 35331740), and extended that comparative work to amphibians more broadly (PMID 41935755).
Study Types at a Glance
| Model or population | What the study examined | Reference |
|---|---|---|
| Healthy human volunteers | Motilin fluctuations measured by liquid chromatography mass spectrometry | PMID 38544692 |
| Children with functional constipation | Serum motilin levels and motilin gene polymorphisms | PMID 27706119 |
| Lactating women and human milk | Motilin in human milk and elevated plasma concentration | PMID 15377298 |
| Dogs | Differential motilin receptor expression along the gastrointestinal tract | PMID 25918525 |
| Human motilin receptor transgenic mice | Effects of motilin receptor agonists and ghrelin | PMID 30934667 |
| Rat incisional pain model | Dorsal horn expression; intrathecal motilin and pain behaviours | PMID 36816129 |
| Quail, pheasant, newt, amphibians | Cloning, identification, distribution, contractility | PMID 27179882, PMID 34506789, PMID 35331740, PMID 41935755 |
| Receptor structure | Structural basis for motilin and erythromycin recognition | PMID 36921049 |
Why Motilin Matters in Peptide Literature
Three features make motilin a recurring reference point. First, it is a peptide whose receptor has been structurally characterised, including how the receptor recognises both the peptide and erythromycin (PMID 36921049). Second, it sits in the same discussion as ghrelin, and the two were compared directly in humanised receptor mice (PMID 30934667). Third, its biology is strongly species-dependent, a theme highlighted by the 2021 comparative review of structure, distribution, receptors and gastrointestinal motility (PMID 34497583) and by functional work showing contractility-stimulating action in birds such as the pheasant (PMID 34506789).
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The verified papers summarised here were largely descriptive, analytical or mechanistic rather than safety trials, and their published titles and abstracts centred on measurement, distribution, receptor structure and motility or pain endpoints; for example, the 2024 healthy-volunteer work reported motilin fluctuations measured by liquid chromatography mass spectrometry rather than tolerability outcomes (PMID 38544692), and the 2023 rat study reported dorsal horn expression and the effect of intrathecal motilin on pain behaviours (PMID 36816129). No adverse-event profile for motilin or motilin receptor agonists in humans can be drawn from this set of references.
Limitations of the Evidence
- Much of the functional data comes from non-human species, including quail (PMID 27179882), pheasant (PMID 34506789) and amphibians (PMID 41935755).
- Receptor pharmacology differs across species, which is why researchers built human motilin receptor transgenic mice for agonist comparisons (PMID 30934667).
- Clinical association work, such as the paediatric functional constipation study of serum levels and gene polymorphisms, is observational in design (PMID 27706119).
- Measured concentrations depend on physiological state, as shown by elevated plasma motilin reported in lactating women (PMID 15377298).
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- Motilin Comparative Study: Structure, Distribution, Receptors, and Gastrointestinal Motility (Frontiers in Endocrinology, 2021)
- Structural basis for motilin and erythromycin recognition by motilin receptor (Science Advances, 2023)
- Motilin fluctuations in healthy volunteers determined by liquid chromatography mass spectrometry (Frontiers in Endocrinology, 2024)
- Effects of Motilin Receptor Agonists and Ghrelin in Human motilin receptor Transgenic Mice (International Journal of Molecular Sciences, 2019)
- Differential expression of motilin receptor in various parts of gastrointestinal tract in dogs (Gastroenterology Research and Practice, 2015)
- Serum motilin levels and motilin gene polymorphisms in children with functional constipation (Minerva Pediatrics, 2021)
- Motilin in human milk and its elevated plasma concentration in lactating women (Journal of Gastroenterology and Hepatology, 2004)
- Motilin and its receptor are expressed in the dorsal horn in a rat model of acute incisional pain: Intrathecal motilin injection alleviates pain behaviors (Frontiers in Neuroscience, 2023)
- Pheasant motilin, its distribution and gastrointestinal contractility-stimulating action in the pheasant (General and Comparative Endocrinology, 2021)
- Molecular cloning of motilin and mechanism of motilin-induced gastrointestinal motility in Japanese quail (General and Comparative Endocrinology, 2016)
- Identification of motilin in Japanese fire bellied newt (General and Comparative Endocrinology, 2022)
- Motilin in amphibians (General and Comparative Endocrinology, 2026)
Frequently asked questions
What is motilin?▾
Motilin is a peptide hormone associated with the gastrointestinal tract. A 2021 comparative review summarised its structure, tissue distribution, receptors and relationship to gastrointestinal motility across species (PMID 34497583). Researchers have studied it alongside ghrelin, and a 2019 study compared motilin receptor agonists with ghrelin in human motilin receptor transgenic mice (PMID 30934667). This answer is educational and not medical advice.
Where is motilin found in the body?▾
A 2021 comparative review described motilin distribution and receptor expression across species (PMID 34497583). In dogs, researchers reported differential motilin receptor expression in various parts of the gastrointestinal tract (PMID 25918525). Motilin has also been detected in human milk, with elevated plasma concentrations reported in lactating women (PMID 15377298), and in rat spinal dorsal horn tissue (PMID 36816129).
Why is erythromycin mentioned in motilin research?▾
A 2023 structural study described the basis for recognition of both motilin and erythromycin by the motilin receptor (PMID 36921049). That work is cited because it addresses at a molecular level how a peptide hormone and a macrolide can engage the same receptor. It was a structural investigation, not a treatment trial, and no clinical recommendation follows from it.
How is motilin measured in studies?▾
Approaches differ by question. A 2024 study determined motilin fluctuations in healthy volunteers using liquid chromatography mass spectrometry (PMID 38544692). A paediatric study instead examined serum motilin levels together with motilin gene polymorphisms in children with functional constipation (PMID 27706119). Animal work has used molecular cloning and tissue identification, for example in Japanese quail (PMID 27179882).
What did animal studies report about motilin and gut contractility?▾
Researchers characterised pheasant motilin along with its distribution and gastrointestinal contractility-stimulating action in the pheasant (PMID 34506789), and cloned motilin while investigating the mechanism of motilin-induced gastrointestinal motility in Japanese quail (PMID 27179882). A 2021 comparative review placed such findings in a cross-species context of structure, distribution, receptors and motility (PMID 34497583).
Has motilin been studied outside the digestive system?▾
Yes. A 2023 rat study reported that motilin and its receptor were expressed in the spinal dorsal horn in a model of acute incisional pain, and that intrathecal motilin injection alleviated pain behaviours in that model (PMID 36816129). Separately, motilin was reported in human milk with elevated plasma concentrations in lactating women (PMID 15377298).
What are the main limits of the motilin literature?▾
Much functional data comes from non-mammalian species such as quail (PMID 27179882), pheasant (PMID 34506789) and amphibians (PMID 41935755), and receptor pharmacology differs between species, which is why humanised receptor mice were used for agonist comparisons (PMID 30934667). Clinical work such as the paediatric constipation study was observational (PMID 27706119). Consult a licensed physician for individual questions.
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References
This page summarises published research for education — it is not medical advice, and nothing here is a recommendation to use, purchase, or dose any substance. Study parameters described are what researchers reported, not instructions. Consult a qualified clinician before any health decision.