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Motilin, a peptide hormone consisting of 22 amino acid residues, was identified in the duodenum of pigs in the 1970s. It is known to induce gastrointestinal contractions during the interdigestive state in mammals. Although the motilin gene has been identified in various animal species, it has not been studied in amphibians. Here, we identified the motilin gene in the Japanese fire bellied newt (Cynops pyrrhogaster), and conducted an analysis of tissue distribution, morphological observations, and physiological experiments. The deduced mature newt motilin comprises 22 amino acid residues, like in mammals and birds. The C-terminus of the newt motilin showed high homology with motilin from other species compared to the N-terminus region, which is considered the bioactive site. Motilin mRNA expression in newts was abundant in the upper small intestine, with notably high motilin mRNA expression found in the pancreas. Motilin-producing cells were found in the mucosal layer of the upper small intestine and existed as two cell types: open-and closed-type cells. Motilin-producing cells in the pancreas were also found to produce insulin but not glucagon. Newt motilin stimulated gastric contractions but not in other parts of the intestines in vitro, and motilin-induced gastric contraction was significantly inhibited by treatment with atropine, a muscarinic acetylcholine receptor antagonist. These results indicate that motilin is also present in amphibians, and that its gastrointestinal contractile effects are conserved in mammals, birds, and amphibians. Additionally, we demonstrated for the first time the existence of pancreatic motilin, suggesting that newt motilin has an additional unknown physiological role., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Motilin (MLN), a 22-amino-acid peptide hormone, is generally present in the mucosa of the upper gastrointestinal (GI) tract, mainly the duodenum of mammals, and it regulates GI motility, especially that related to interdigestive migrating contraction. However, MLN and its receptor are absent in mice and rats, and MLN does not cause any mechanical responses in the rat and mouse GI tracts. The guinea-pig is also a rodent, but expression of the MLN gene in the guinea-pig has been reported. In the present study, two guinea-pig MLNs, FIPIFTYSELRRTQEREQNKGL found in the Ensemble Genome Database (gpMLN-1) and FVPIFTYSELRRTQEREQNKRL reported by Xu et al. (2001) (gpMLN-2), were synthesized, and their biological activities were evaluated in the rabbit duodenum and guinea-pig GI tract in vitro. Both gpMLNs showed contractile activity in longitudinal muscle strips of the rabbit duodenum. The EC 50 values of gpMLN-1 and gpMLN-2 were slightly higher than that of human MLN (hMLN), but the maximum contractions were as same as that of hMLN. Treatment with GM109 and hMLN-induced receptor desensitization decreased the contractile activity of both gpMLNs, indicating that the two gpMLN candidates are able to activate the MLN receptor (MLN-R) of the rabbit duodenum. In guinea-pig GI preparations, hMLN and gpMLNs did not show any mechanical responses in circular muscle strips from the gastric antrum or in longitudinal strips of the duodenum, ileum and colon although acetylcholine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) caused definite mechanical responses. The DMPP-induced neural responses in the gastric circular muscle and ileal longitudinal muscles were not modified by gpMLN-1. Even in the gastric and ileal strips with intact mucosa, no mechanical responses were seen with either of the gpMLNs. Furthermore, RT-PCR using various primer sets failed to amplify the gpMLN-2 mRNA. In conclusion, gpMLNs including one that was already reported and the other that was newly found in a database were effective to the rabbit MLN-R, whereas they did not cause any contractions or modification of neural responses in the guinea-pig GI tract, indicating that the MLN system is vestigial and not functional in regulation of GI motility in the guinea-pig as well as in other rodents such as rats and mice., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Motilin, a peptide hormone produced in the upper intestinal mucosa, plays an important role in the regulation of gastrointestinal (GI) motility. In the present study, we first determined the cDNA and amino acid sequences of motilin in the Japanese quail and studied the distribution of motilin-producing cells in the gastrointestinal tract. We also examined the motilin-induced contractile properties of quail GI tracts using an in vitro organ bath, and then elucidated the mechanisms of motilin-induced contraction in the proventriculus and duodenum of the quail. Mature quail motilin was composed of 22 amino acid residues, which showed high homology with chicken (95.4%), human (72.7%), and dog (72.7%) motilin. Immunohistochemical analysis showed that motilin-immunopositive cells were present in the mucosal layer of the duodenum (23.4±4.6cells/mm(2)), jejunum (15.2±0.8cells/mm(2)), and ileum (2.5±0.7cells/mm(2)), but were not observed in the crop, proventriculus, and colon. In the organ bath study, chicken motilin induced dose-dependent contraction in the proventriculus and small intestine. On the other hand, chicken ghrelin had no effect on contraction in the GI tract. Motilin-induced contraction in the duodenum was not inhibited by atropine, hexamethonium, ritanserin, ondansetron, or tetrodotoxin. However, motilin-induced contractions in the proventriculus were significantly inhibited by atropine and tetrodotoxin. These results suggest that motilin is the major stimulant of GI contraction in quail, as it is in mammals and the site of action of motilin is different between small intestine and proventriculus., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The migrating motor complex (MMC) is responsible for emptying the stomach during the interdigestive period, in preparation for the next meal. It is known that gastric phase III of MMC starts from the proximal stomach and propagates the contraction downwards. We hypothesized that a certain region of the stomach must be more responsive to motilin than others, and that motilin-induced strong gastric contractions propagate from that site. Stomachs of the Suncus or Asian house shrew, a small insectivorous mammal, were dissected and the fundus, proximal corpus, distal corpus, and antrum were examined to study the effect of motilin using an organ bath experiment. Motilin-induced contractions differed in different parts of the stomach. Only the proximal corpus induced gastric contraction even at motilin 10(-10) M, and strong contraction was induced by motilin 10(-9) M in all parts of the stomach. The GPR38 mRNA expression was also higher in the proximal corpus than in the other sections, and the lowest expression was observed in the antrum. GPR38 mRNA expression varied with low expression in the mucosal layer and high expression in the muscle layer. Additionally, motilin-induced contractions in each dissected part of the stomach were inhibited by tetrodotoxin and atropine pretreatment. These results suggest that motilin reactivity is not consistent throughout the stomach, and an area of the proximal corpus including the cardia is the most sensitive to motilin.

Background: Gastric acidification inhibits motilin-induced gastric phase III contractions. However, the underlying mechanism has not been thoroughly investigated. Here, we studied the inhibitory mechanism by gastric acidification on motilin-induced contraction in Suncus murinus (S. murinus)., Methods: We measured interdigestive gastric phase III contractions in conscious, freely moving S. murinus, and examined the inhibitory effect of gastric acidification on motilin action and the involvement of the vagus nerve and transient receptor potential vanilloid receptor 1 (TRPV1) in the inhibitory mechanism., Results: A bolus injection of motilin evoked phase III-like contractions during intravenous infusion of saline. Intragastric acidification (pH 1.5-2.5) inhibited motilin-induced phase III contractions in a pH-dependent manner and significantly decreased the motility index at a pH below 2.0. In contrast, intraduodenal acidification (pH 2.0) failed to inhibit motilin-induced contractions. Vagotomy significantly alleviated the suppression of motilin-induced gastric contractions under acidic conditions (pH 2.0), suggesting vagus nerve involvement. Moreover, intragastric acidification (pH 2.0) significantly increased the number of c-Fos-positive cells in the nucleus tractus solitarii. In vagotomized S. murinus, the number of c-Fos-positive cells did not change, even under gastric acidification conditions. TRPV1 mRNA was highly expressed in the muscle and mucosal regions of the antrum and the nodose ganglion, whereas was not detected in the upper small intestine. Capsazepin, a TRPV1 antagonist, completely rescued the inhibitory effect of gastric acidification., Conclusions: Gastric acidification in S. murinus inhibits motilin-induced contractions, a finding similar to results observed in humans, while TRPV1-expressing vagus nerves play a role in the inhibitory mechanism.

Motilin was discovered in the 1970s as the most important hormone for stimulating strong gastric contractions; however, the mechanisms by which motilin causes gastric contraction are not clearly understood. Here, we determined the coordinated action of motilin and ghrelin on gastric motility during fasted and postprandial contractions by using house musk shrew (Suncus murinus; order: Insectivora, suncus named as the laboratory strain). Motilin-induced gastric contractions at phases I and II of the migrating motor complex were inhibited by pretreatment with (D-Lys(3))-GHRP-6 (6 mg/kg/h), a ghrelin receptor antagonist. Administration of the motilin receptor antagonist MA-2029 (0.1 mg/kg) and/or (D-Lys(3))-GHRP-6 (0.6 mg/kg) at the peak of phase III abolished the spontaneous gastric phase III contractions in vivo. Motilin did not stimulate gastric contractions in the postprandial state. However, in the presence of a low dose of ghrelin, motilin evoked phase III-like gastric contractions even in the postprandial state, and postprandial gastric emptying was accelerated. In addition, pretreatment with (D-Lys(3))-GHRP-6 blocked the motilin-induced gastric contraction in vitro and in vivo, and a γ-aminobutyric acid (GABA) antagonist reversed this block in gastric contraction. These results indicate that blockade of the GABAergic pathway by ghrelin is essential for motilin-induced gastric contraction.

Motilin and ghrelin are gastrointestinal hormones that stimulate the migrating motor complex (MMC) of gastrointestinal motility during the fasting state. In this study, we examined the effect of motilin and ghrelin on pepsinogen secretion in anesthetized suncus (house musk shrew, Suncus murinus), a ghrelin- and motilin-producing mammal. By using a gastric lumen-perfusion system, we found that the intravenous administration of carbachol and motilin stimulated pepsinogen secretion, the latter in a dose-dependent manner, whereas ghrelin had no effect. We then investigated the pathways of motilin-induced pepsinogen secretion using acetylcholine receptor antagonists. Treatment with atropine, a muscarinic acetylcholine receptor antagonist, completely inhibited both carbachol and motilin-induced pepsinogen secretion. Motilin-induced pepsinogen secretion was observed in the vagotomized suncus. This is the first report demonstrating that motilin stimulates pepsinogen secretion, and suggest that this effect occurs through a cholinergic pathway in suncus., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Motilin and ghrelin constitute a peptide family, and these hormones are important for the regulation of gastrointestinal motility. In this study, we examined the effect of motilin and ghrelin on gastric acid secretion in anesthetized suncus (house musk shrew, Suncus murinus), a ghrelin- and motilin-producing mammal. We first established a gastric lumen-perfusion system in the suncus and confirmed that intravenous (i.v.) administration of histamine (1 mg/kg body weight) stimulated acid secretion. Motilin (0.1, 1.0, and 10 μg/kg BW) stimulated the acid output in a dose-dependent manner in suncus, whereas ghrelin (0.1, 1.0, and 10 μg/kg BW) alone did not induce acid output. Furthermore, in comparison with the vehicle administration, the co-administration of low-dose (1 μg/kg BW) motilin and ghrelin significantly stimulated gastric acid secretion, whereas either motilin (1 μg/kg BW) or ghrelin (1 μg/kg BW) alone did not significantly induce gastric acid secretion. This indicates an additive role of ghrelin in motilin-induced gastric acid secretion. We then investigated the pathways of motilin/motilin and ghrelin-stimulated acid secretion using receptor antagonists. Treatment with YM 022 (a CCK-B receptor antagonist) and atropine (a muscarinic acetylcholine receptor antagonist) had no effect on motilin or motilin-ghrelin co-administration-induced acid output. In contrast, famotidine (a histamine H2 receptor antagonist) completely inhibited motilin-stimulated acid secretion and co-administration of motilin and ghrelin induced gastric acid output. This is the first report demonstrating that motilin stimulates gastric secretion in mammals. Our results also suggest that motilin and co-administration of motilin and ghrelin stimulate gastric acid secretion via the histamine-mediated pathway in suncus.

The upper gastrointestinal (GI) tract undergoes a temporally coordinated cyclic motor pattern known as the migrating motor complex (MMC) in both dogs and humans during the fasted state. Feeding results in replacement of the MMC by a pattern of noncyclic, intermittent contractile activity termed as postprandial contractions. Although the MMC is known to be stimulated by motilin, recent studies have shown that ghrelin, which is from the same peptide family as motilin, is also involved in the regulation of the MMC. In the present study, we investigated the role of the vagus nerve on gastric motility using conscious suncus-a motilin- and ghrelin-producing small animal. During the fasted state, cyclic MMC comprising phases I, II, and III was observed in both sham-operated and vagotomized suncus; however, the duration and motility index (MI) of phase II was significantly decreased in vagotomized animals. Motilin infusion (50 ng·kg(-1)·min(-1) for 10 min) during phase I had induced phase III-like contractions in both sham-operated and vagotomized animals. Ghrelin infusion (0.1, 0.3, 1, 3, or 10 µg·kg(-1)·min(-1) for 10 min) enhanced the amplitude of phase II MMC in sham-operated animals, but not in vagotomized animals. After feeding, phase I was replaced by postprandial contractions, and motilin infusion (50 ng·kg(-1)·min(-1) for 10 min) did not induce phase III-like contractions in sham-operated suncus. However, in vagotomized suncus, feeding did not evoke postprandial contractions, but exogenous motilin injection strongly induced phase III-like contractions, as noted during the phase I period. Thus, the results indicate that ghrelin stimulates phase II of the MMC via the vagus nerve in suncus. Furthermore, the vagus nerve is essential for initiating postprandial contractions, and inhibition of the phase III-like contractions induced by motilin is highly dependent on the vagus nerve.

Motilin and ghrelin are the gastrointestinal (GI) hormones released in a fasting state to stimulate the GI motility of the migrating motor complex (MMC). We focused on coordination of the ghrelin/motilin family in gastric contraction in vivo and in vitro using the house musk shrew (Suncus murinus), a ghrelin- and motilin-producing mammal. To measure the contractile activity of the stomach in vivo, we recorded GI contractions either in the free-moving conscious or anesthetized S. murinus and examined the effects of administration of motilin and/or ghrelin on spontaneous MMC in the fasting state. In the in vitro study, we also studied the coordinative effect of these hormones on the isolated stomach using an organ bath. In the fasting state, phase I, II, and III contractions were clearly recorded in the gastric body (as observed in humans and dogs). Intravenous infusion of ghrelin stimulated gastric contraction in the latter half of phase I and in the phase II in a dose-dependent manner. Continuous intravenous infusion of ghrelin antagonist (d-Lys3-GHRP6) significantly suppressed spontaneous phase II contractions and prolonged the time of occurrence of the peak of phase III contractions. However, intravenous infusion of motilin antagonist (MA-2029) did not inhibit phase II contractions but delayed the occurrence of phase III contractions of the MMC. In the in vitro study, even though a high dose of ghrelin did not stimulate contraction of stomach preparations, ghrelin administration (10(-10)-10(-7) M) with pretreatment of a low dose of motilin (10(-10) M) induced gastric contraction in a dose-dependent manner. Pretreatment with 10(-8) M ghrelin enhanced motilin-stimulated gastric contractions by 10 times. The interrelation of these peptides was also demonstrated in the anesthetized S. murinus. The results suggest that ghrelin is important for the phase II contraction and that coordination of motilin and ghrelin are necessary to initiate phase III contraction of the MMC.

Although many studies have demonstrated the action of motilin on migrating motor complex by using human subjects and relatively large animals, the precise physiological mechanisms of motilin remain obscure. One reason for the lack of progress in this research field is that large animals are generally not suitable for molecular-level study. To overcome this problem, in this study, we focused on the house musk shrew (Suncus murinus, order: Insectivora, suncus named as laboratory strain) as a small model animal, and we present here the results of motilin gene cloning and its availability for motilin study. The motilin gene has a high homology sequence with that of other mammals, including humans. Suncus motilin is predicted to exist as a 117-residue prepropeptide that undergoes proteolytic cleavage to form a 22-amino-acid mature peptide. The results of RT-PCR showed that motilin mRNA is highly expressed in the upper small intestine, and low levels of expression were found in many tissues. Morphological analysis revealed that suncus motilin-producing cells were present in the upper small intestinal mucosal layer but not in the myenteric plexus. Administration of suncus motilin to prepared muscle strips of rabbit duodenum showed almost the same contractile effect as that of human motilin. Moreover, suncus stomach preparations clearly responded to suncus or human motilin stimulation. To our knowledge, this is the first report that physiological active motilin was determined in small laboratory animals, and the results of this study suggest that suncus is a suitable model animal for studying the motilin-ghrelin family.

Motilin, a 22‐amino‐acid peptide produced in the upper small intestine, induces strong gastric contraction in fasted state. In many rodents, motilin and its cognate receptors exist as pseudogenes, which has delayed motilin research in the past decades. Recently, the house musk shrew (Suncus murinus) was developed as a useful model for studying motilin and gastrointestinal motility. However, due to a lack of motilin‐producing cell lines and difficulties in culturing small intestinal cells, the regulatory mechanisms of motilin secretion and its messenger RNA (mRNA) transcription have remained largely unclear. In this study, we generated small intestinal organoids from S. murinus for the first time. Using methods similar to mouse organoid generation, we found crypt‐like budding structures 3 days after isolating intestinal tissues. The organoids grew gradually with time. In addition, the generated organoids were able to be passaged and maintained for 6 months or longer. Motilin messenger RNA (mRNA) and immunopositive cells were observed in both S. murinus intestinal organoids and primary tissues. This is the first report of intestinal organoids in S. murinus, and our results suggest that S. murinus intestinal organoids could be useful for analyzing motilin secretion and transcription. [ABSTRACT FROM AUTHOR]

Abstract: We previously identified ghrelin and motilin genes in Suncus murinus (suncus), and also revealed that motilin induces phase III-like strong contractions in the suncus stomach in vivo, as observed in humans and dogs. Moreover, repeated migrating motor complexes were found in the gastrointestinal tract of suncus at regular 120-min intervals. We therefore proposed suncus as a small laboratory animal model for the study of gastrointestinal motility. In the present study, we identified growth hormone secretagogue receptor (GHS-R) and motilin receptor (GPR38) genes in the suncus. We also examined their tissue distribution throughout the body. The amino acids of suncus GHS-R and GPR38 showed high homology with those of other mammals and shared 42% amino acid identity. RT-PCR showed that both the receptors were expressed in the hypothalamus, medulla oblongata, pituitary gland and the nodose ganglion in the central nervous system. In addition, GHS-R mRNA expressions were detected throughout the stomach and intestine, whereas GPR38 was expressed in the gastric muscle layer, lower intestine, lungs, heart, and pituitary gland. These results suggest that ghrelin and motilin affect gut motility and energy metabolism via specific receptors expressed in the gastrointestinal tract and/or in the central nervous system of suncus. [Copyright &y& Elsevier]

Abstract: Motilin is a peptide hormone involved in gastrointestinal motility. GPR38, initially cloned as an orphan receptor, is now considered a specific receptor for motilin. Previously, molecular characterization of the motilin receptor had only been performed in mammalian and fish species. In this study, we cloned cDNA for chicken motilin receptor from the duodenum and characterized its primary structure, tissue distribution, and biological activity. The cDNA encoded 349 amino acids showing significant overall sequence identity to mammalian motilin receptors. Chicken motilin increased intracellular Ca2+ concentration in human embryonic kidney (HEK) 293 cells transiently expressing the recombinant chicken motilin receptor. Comparison of the cDNA sequence with the genomic sequence of chicken motilin receptor revealed that the chicken motilin receptor gene consists of two exons separated by an intron. Real-time PCR analysis showed that chicken motilin receptor mRNA is expressed in a wide range of tissues in 21-day-old chickens, with markedly high levels in the proventriculus, duodenum, and oviduct. The expression levels of the mRNA in the proventriculus and duodenum were highest just before hatching and rapidly decreased during post-hatch development. These results suggest that chicken motilin receptor is largely involved in gastrointestinal functions at pre- and post-hatch periods through an intracellular signaling pathway accompanied by an increase in Ca2+ levels. [Copyright &y& Elsevier]