Isolation, sequence, and bioactivity of chicken motilin

Molecular characterization and distribution of motilin and motilin receptor in the Japanese medaka Oryzias latipes

Motilin (MLN) is a peptide hormone originally isolated from the mucosa of the porcine intestine. Its orthologs have been identified in various vertebrates. Although MLN regulates gastrointestinal motility in tetrapods from amphibians to mammals, recent studies indicate that MLN is not involved in the regulation of isolated intestinal motility in zebrafish, at least in vitro. To determine the unknown function of MLN in teleosts, we examined the expression of MLN and the MLN receptor (MLNR) at the cellular level in Japanese medaka (Oryzias latipes). Quantitative PCR revealed that mln mRNA was limitedly expressed in the gut, whereas mlnr mRNA was not detected in the gut but was expressed in the brain and kidney. By in situ hybridization and immunohistochemistry, mlnr mRNA was detected in the dopaminergic neurons of the area postrema in the brain and the noradrenaline-producing cells in the interrenal gland of the kidney. Furthermore, we observed efferent projections of mlnr-expressing dopaminergic neurons in the lobus vagi (XL) and nucleus motorius nervi vagi (NXm) of the medulla oblongata by establishing a transgenic medaka expressing the enhanced green fluorescence protein driven by the mlnr promoter. The expression of dopamine receptor mRNAs in the XL and cholinergic neurons in NXm was confirmed by in situ hybridization. These results indicate novel sites of MLN activity other than the gastrointestinal tract. MLN may exert central and peripheral actions through the regulation of catecholamine release in medaka.

Motilin, a Novel Orexigenic Factor, Involved in Feeding Regulation in Yangtze Sturgeon (Acipenser dabryanus)

Motilin is a gastrointestinal hormone that is mainly produced in the duodenum of mammals, and it is responsible for regulating appetite. However, the role and expression of motilin are poorly understood during starvation and the weaning stage, which is of great importance in the seeding cultivation of fish. In this study, the sequences of Yangtze sturgeon (Acipenser dabryanus Motilin (AdMotilin)) motilin receptor (AdMotilinR) were cloned and characterized. The results of tissue expression showed that by contrast with mammals, AdMotilin mRNA was richly expressed in the brain, whereas AdMotilinR was highly expressed in the stomach, duodenum, and brain. Weaning from a natural diet of T. Limnodrilus to commercial feed significantly promoted the expression of AdMotilin in the brain during the period from day 1 to day 10, and after re-feeding with T. Limnodrilus the change in expression of AdMotilin was partially reversed. Similarly, it was revealed that fasting increased the expression of AdMotilin in the brain (3 h, 6 h) and duodenum (3 h), and the expression of AdMotilinR in the brain (1 h) in a time-dependent manner. Furthermore, it was observed that peripheral injection of motilin-NH2 increased food intake and the filling index of the digestive tract in the Yangtze sturgeon, which was accompanied by the changes of AdMotilinR and appetite factors expression in the brain (POMC, CART, AGRP, NPY and CCK) and stomach (CCK). These results indicate that motilin acts as an indicator of nutritional status, and also serves as a novel orexigenic factor that stimulates food intake in Acipenser dabryanus. This study lays a strong foundation for the application of motilin as a biomarker in the estimation of hunger in juvenile Acipenser dabryanu during the weaning phase, and enhances the understanding of the role of motilin as a novel regulator of feeding in fish.

Motilin is a regulator of gastric contraction in Japanese fire belly newts (Cynops pyrrhogaster), in vitro studies using isolated gastrointestinal strips of newts, rabbits, and chickens

The effects of newt motilin on the contractility of the isolated gastrointestinal (GI) tract from Japanese fire belly newts (newt) were examined to clarify whether motilin regulates GI motility in urodele amphibians. In addition, contractile responsiveness to motilins from seven species of vertebrates (human, chicken, turtle, alligator, axolotol, newt and zebrafish) were compared in GI preparations from three different animals (rabbit duodenum, chicken ileum and newt stomach) to determine the species-specific action of motilin. Newt motilin (10^-10 M - 10^-6 M) caused a contraction of cognate gastric strips, while the upper, middle, and lower intestinal strips were insensitive. The rank order of motilins for contractile activity in newt gastric strips was newt > alligator > axolotol > chicken > turtle > human ≫ zebrafish. On the other hand, newt motilin caused a weak contraction in the rabbit duodenum (human > alligator = chicken > turtle > newt ≧ axolotol > zebrafish), and it was ineffective in the chicken ileum (chicken > turtle > alligator > human ≫ newt, axolotol and zebrafish). This study demonstrates that motilin induces contraction in the GI tract of a urodele amphibian, the newt, in a region (stomach)-specific manner and further indicates that a ligand-receptor interaction of the motilin system is a species-specific manner probably due to differences in the amino acid sequence of motilin.

Identification of motilin in Japanese fire bellied newt

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.

Pheasant motilin, its distribution and gastrointestinal contractility-stimulating action in the pheasant

Previously, pheasant motilin was identified as a 22-amino acid peptide with a sequence of FVPFFTQSDI QKMQEKERIK GQ. In the present study, the distribution of pheasant motilin mRNA was determined and compared with that of ghrelin, a motilin-related peptide. The effects of pheasant motilin on the cognate gastrointestinal (GI) muscle strips were also examined in an in vitro contraction study. The expression of pheasant motilin mRNA was highest in the small intestine (duodenum, jejunum and ileum), moderate in the colon and very low in the brain, lung, heart, pancreas, esophagus, proventriculus, gizzard and caecum, and this distribution was in contrast with that of ghrelin mRNA. Pheasant motilin caused contraction of the cognate GI tract in a region-dependent manner, similar to chicken motilin. The contraction in the small intestine was large and was not affected by atropine. In contrast, contraction in the proventriculus was small and was decreased by atropine. The crop and colon were insensitive to pheasant motilin. Neither GM109 nor MA2029, mammalian motilin receptor antagonists inhibited the contractions of pheasant motilin. Erythromycin was ineffective in the pheasant ileum, although it caused contraction of the rabbit duodenum. These results indicate that pheasant motilin caused contraction through an action on smooth muscles in the small intestine and an action on enteric cholinergic nerves in the proventriculus. This high responsiveness of the small intestine suggests that motilin is a regulator of small intestinal motility in avians, and the characteristic of the motilin receptor in the pheasant might be different from that in mammals, as is that in chickens.

Motilin Comparative Study: Structure, Distribution, Receptors, and Gastrointestinal Motility

Motilin, produced in endocrine cells in the mucosa of the upper intestine, is an important regulator of gastrointestinal (GI) motility and mediates the phase III of interdigestive migrating motor complex (MMC) in the stomach of humans, dogs and house musk shrews through the specific motilin receptor (MLN-R). Motilin-induced MMC contributes to the maintenance of normal GI functions and transmits a hunger signal from the stomach to the brain. Motilin has been identified in various mammals, but the physiological roles of motilin in regulating GI motility in these mammals are well not understood due to inconsistencies between studies conducted on different species using a range of experimental conditions. Motilin orthologs have been identified in non-mammalian vertebrates, and the sequence of avian motilin is relatively close to that of mammals, but reptile, amphibian and fish motilins show distinctive different sequences. The MLN-R has also been identified in mammals and non-mammalian vertebrates, and can be divided into two main groups: mammal/bird/reptile/amphibian clade and fish clade. Almost 50 years have passed since discovery of motilin, here we reviewed the structure, distribution, receptor and the GI motility regulatory function of motilin in vertebrates from fish to mammals.

Motilin- and ghrelin-induced contractions in isolated gastrointestinal strips from three species of frogs

Ghrelin (GHRL) and motilin (MLN), gut peptides isolated from the mucosa of the stomach and duodenum, respectively, stimulate gastrointestinal (GI) motility in mammals and birds. However, the functions of MLN and GHRL in amphibian GI tracts have not been examined in detail. To clarify the regulation of GI motility by the two peptides, the effects of human MLN and rat GHRL on contractility of isolated GI strips from three species of frogs, the black-spotted pond frog (pond frog; Pelophylax nigromaculata), bullfrog (Lithobates catesbeiana) and Western clawed frog (Xenopus; Xenopus tropicalis), were examined in in vitro experiments. The GI tract of each frog was divided into the stomach, upper intestine, middle intestine and lower intestine. Human MLN caused contractions of the stomach in the pond frog and upper intestine in the bullfrog and Xenopus, but other GI regions were insensitive to human MLN. Erythromycin did not cause contraction of the upper intestine of the bullfrog and Xenopus. Rat GHRL did not cause contraction of the stomach and small intestines in the pond frog and bullfrog, but it caused a concentration-dependent contraction in the stomach and upper intestine of Xenopus, while des-acyl rat GHRL did not cause any contraction of them. In conclusion, human MLN caused the contraction of the stomach or upper intestine in the three species of frogs, but GHRL was effective only in the stomach and upper intestine of Xenopus. On the basis of these data, MLN but not GHRL causes the GI region-dependent contractions in the frogs.

Regulation of Gastrointestinal Motility by Motilin and Ghrelin in Vertebrates

The energy balance of vertebrates is regulated by the difference in energy input and energy expenditure. Generally, most vertebrates obtain their energy from nutrients of foods through the gastrointestinal (GI) tract. Therefore, food intake and following food digestion, including motility of the GI tract, secretion and absorption, are crucial physiological events for energy homeostasis. GI motility changes depending on feeding, and GI motility is divided into fasting (interdigestive) and postprandial (digestive) contraction patterns. GI motility is controlled by contractility of smooth muscles of the GI tract, extrinsic and intrinsic neurons (motor and sensory) and some hormones. In mammals, ghrelin (GHRL) and motilin (MLN) stimulate appetite and GI motility and contribute to the regulation of energy homeostasis. GHRL and MLN are produced in the mucosal layer of the stomach and upper small intestine, respectively. GHRL is a multifunctional peptide and is involved in glucose metabolism, endocrine/exocrine functions and cardiovascular and reproductive functions, in addition to feeding and GI motility in mammals. On the other hand, the action of MLN is restricted and species such as rodentia, including mice and rats, lack MLN peptide and its receptor. From a phylogenetic point of view, GHRL and its receptor GHS-R1a have been identified in various vertebrates, and their structural features and various physiological functions have been revealed. On the other hand, MLN or MLN-like peptide (MLN-LP) and its receptors have been found only in some fish, birds and mammals. Here, we review the actions of GHRL and MLN with a focus on contractility of the GI tract of species from fish to mammals.

Does motilin peptide regulate gastrointestinal motility of zebrafish? An in vitro study using isolated intestinal strips

Motilin (MOT), a 22-amino-acid peptide hormone produced in the duodenal mucosa, stimulates gastrointestinal motility in mammals and birds, and it is a mediator of interdigestive motor complexes. Recently, expression of MOT-like peptide (MOTLP) and its receptor mRNAs was identified in zebrafish. The aim of the present study was to determine whether the zebrafish MOTLP (zfMOTLP, HIAFFSPKEMRELREKE) affects zebrafish gastrointestinal motility, with comparison to the effect of human MOT, in which five amino acids are identical to zfMOTLP at positions 5, 9, 15, 16, and 17. zfMOTLP caused small contractions of the rabbit duodenum and chicken ileum but, the sensitivity was about 3000-times lower than that of human MOT. zfMOTLP-induced contraction in the rabbit duodenum was decreased by pretreatment of the MOT receptor antagonist GM109, indicating that zfMOTLP could bind to the MOT receptor. zfMOTLP (3-100nM) increased the intracellular Ca²⁺ concentration in zfMOT receptor-expressing HEK293 cells, but human MOT did not cause responses even at 100nM. In in vitro study using isolated zebrafish gastrointestinal strips, zfMOTLP caused only small contractions even at high doses (1-10μM). zfMOT receptor mRNA is detected in the gastrointestinal tract and brain to almost the same extent, and the expression level (40-70 copies/100ng total RNA) is much lower than that in the chicken gastrointestinal tract. These results suggest that the MOTLP/MOT receptor system is present in zebrafish, but its physiological role for regulation of gastrointestinal motility might be not significant due to the weak contractile activity and low expression level of the receptor.

Molecular cloning of motilin and mechanism of motilin-induced gastrointestinal motility in Japanese quail

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.

Effects of ghrelin and motilin on smooth muscle contractility of the isolated gastrointestinal tract from the bullfrog and Japanese fire belly newt

Ghrelin has been identified in some amphibians and is known to stimulate growth hormone release and food intake as seen in mammals. Ghrelin regulates gastrointestinal motility in mammals and birds. The aim of this study was to determine whether ghrelin affects gastrointestinal smooth muscle contractility in bullfrogs (anuran) and Japanese fire belly newts (urodelian) in vitro. Neither bullfrog ghrelin nor rat ghrelin affected longitudinal smooth muscle contractility of gastrointestinal strips from the bullfrog. Expression of growth hormone secretagogue receptor 1a (GHS-R1a) mRNA was confirmed in the bullfrog gastrointestinal tract, and the expression level in the gastric mucosa was lower than that in the intestinal mucosa. In contrast, some gastrointestinal peptides, including substance P, neurotensin and motilin, and the muscarinic receptor agonist carbachol showed marked contraction, indicating normality of the smooth muscle preparations. Similar results were obtained in another amphibian, the Japanese fire belly newt. Newt ghrelin and rat ghrelin did not cause any contraction in gastrointestinal longitudinal muscle, whereas substance P and carbachol were effective causing contraction. In conclusion, ghrelin does not affect contractility of the gastrointestinal smooth muscle in anuran and urodelian amphibians, similar to results for rainbow trout and goldfish (fish) but different from results for rats and chickens. The results suggest diversity of ghrelin actions on the gastrointestinal tract across animals. This study also showed for the first time that motilin induces gastrointestinal contraction in amphibians.

Association between Motilin Receptor Gene Haplotypes and Growth Traits in Japanese Hinai-dori Crossbred Chickens

We previously identified quantitative trait loci (QTL) for body weight and average daily gain in a common region between ADL0198 (chr 1: 171.7 Mb) and ABR0287 (chr 1: 173.4 Mb) on chicken chromosome 1 in an F₂ resource population produced by crossing low- and high-growth lines of the Hinai-dori breed. Motilin receptor (MLNR) is a candidate gene affecting growth traits in the region. In this study, we genotyped polymorphisms of the MLNR gene and investigated its association with growth traits in a Hinai-dori F₂ intercross population. All the exons of the MLNR gene in the parental population were subjected to PCR amplification, nucleotide sequenced and haplotypes identified. To distinguish resultant diplotype individuals in the F₂ population, a mismatch amplification mutation assay was performed. Three haplotypes (Haplotypes 1–3) were accordingly identified. Six genotypes produced by the combination of three haplotypes (Haplotype 1, 2, and 3) were examined in order to identify associations between MLNR haplotypes and growth traits. The data showed that Haplotype 1 was superior to Haplotype 2 and 3 in body weight at 10 and 14 weeks of age, average daily gain between 4 and 10 weeks, 10 and 14 weeks, and 0 and 14 weeks of age in female in F₂ females. It was concluded that MLNR is a useful marker of growth traits and could be used to develop strategies for improving growth traits in the Hinai-dori breed.

Age-dependent reduction of ghrelin- and motilin-induced contractile activity in the chicken gastrointestinal tract

Ghrelin is an endogenous ligand for growth hormone secretagogue-receptor 1a (GHS-R1a) and stimulates gastrointestinal (GI) motility in the chicken. Since ghrelin stimulates GH release, which regulates growth, it might be interesting to compare ghrelin-induced responses in GI tract of different-aged chickens. Motilin is a ghrelin-related gut peptide that induces strong contraction in the small intestine. Aim of this study was to clarify age-dependent changes in ghrelin- and motilin-induced contractions of the chicken GI tract and expression of their receptor mRNAs. Chicken ghrelin caused contraction of the crop and proventriculus. Ghrelin-induced contraction in the proventriculus decreased gradually up to 100 days after hatching, but the responses to ghrelin in the crop were the same during the growth period. GHS-R1a mRNA expression in the crop tended to increase, but that in the proventriculus decreased depending on the age. Chicken motilin caused contraction of the chicken GI tract. Atropine decreased the responses to motilin in the proventriculus but not in the ileum. Motilin-induced contraction in the proventriculus but not that in the ileum decreased depending on post-hatching days. On the other hand, motilin receptor mRNA expression in every region of the GI tract decreased with age, but the decrease was more marked in the proventriculus than in the ileum. In conclusion, ghrelin- and motilin-induced GI contractions selectively decreased in the chicken proventriculus depending on post-hatching days, probably due to the age-related decrease in respective receptors expression. The results suggest an age-related contribution of ghrelin and motilin to the regulation of chicken GI motility.

Molecular identification of GHS-R and GPR38 in Suncus murinus

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.

Myenteric neural network activated by motilin in the stomach of Suncus murinus (house musk shrew)

BACKGROUND

It has been shown in human and canine studies that motilin, a gastroprokinetic hormone, induces gastric phase III contractions via the enteric nervous; however, the center of motilin action in the stomach has not been clearly revealed. In the present study, we investigated the neural pathway of motilin-induced gastric contraction by using Suncus murinus, a new animal model for motilin study.

METHODS

An isolated suncus stomach was used in vitro to determine the mechanism of motilin action through the myenteric plexus. Synthetic suncus motilin (10(-11) -10(-7) molL(-1) ) was added to an organ bath, and the spontaneous contraction response was expressed as a percent of ACh (10(-5) molL(-1) ) responses. Motilin-induced contractions were also studied by a pharmacological method using several receptor antagonists and enzyme inhibitor.

KEY RESULTS

Suncus motilin induced a concentration-dependent gastric contraction at concentrations from 10(-9) to 10(-7) molL(-1) . The responses to suncus motilin in the stomach were completely abolished by atropine and tetrodotoxin treatment and significantly suppressed by administration of hexamethonium, verapamil, phentolamine, yohimbine, ondansetron, and naloxone, whereas ritanserin, prazosin, timolol, and FK888 did not affect the action of motilin. Additionally, N-nitro l-arginine methylester slightly potentiated the contractions induced by motilin.

CONCLUSIONS & INFERENCES

The results indicate that motilin directly stimulates and modulates suncus gastric contraction through cholinergic, adrenergic, serotonergic, opioidergic, and NO neurons in the myenteric plexus.

Erythromycin inhibited glycinergic inputs to gastric vagal motoneurons in brainstem slices of newborn rats

BACKGROUND

Motilin has been known to stimulate the motility of digestive organs peripherally via activation of motilin receptors located at gastrointestinal (GI) cholinergic nerve endings and/or smooth muscle cells. Recent studies have indicated that motilin may also promote GI motility via actions in the central nervous system; however the sites of action and the mechanisms are not clear yet. The present study aimed to test the hypothesis that motilin receptor agonist erythromycin alters the synaptic inputs of preganglionic gastric vagal motoneurons (GVMs) located in the dorsal motor nucleus of the vagus (DMV).

METHODS

Gastric vagal motoneurons were retrogradely labeled by fluorescent tracer from the stomach wall of newborn rats. Fluorescently labeled GVMs in DMV were recorded using whole-cell patch-clamp in brainstem slices and the effects of motilin receptor agonist erythromycin on the synaptic inputs were examined.

KEY RESULTS

Erythromycin (100 nmol L(-1), 1 μmol L(-1), 10 μmol L(-1)) significantly inhibited the frequency of glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of GVMs and significantly inhibited the amplitude at the concentration of 10 μmol L(-1). These responses were prevented by GM-109, a selective motilin receptor antagonist. In the pre-existence of tetradotoxin (TTX, 1 μmol L(-1)), erythromycin (10 μmol L(-1)) caused significant decreases of the glycinergic miniature inhibitory postsynaptic currents (mIPSCs), in both the frequency and the amplitude. However, erythromycin (10 μmol L(-1)) didn't cause significant changes of the GABAergic sIPSCs.

CONCLUSIONS & INFERENCES

Erythromycin selectively inhibits the glycinergic inputs of GVMs.

Primary structure, tissue distribution, and biological activity of chicken motilin receptor

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.

Contractile effects of ghrelin-related peptides on the chicken gastrointestinal tract in vitro

Ghrelin is an endogenous ligand for growth hormone secretagogue receptor (GHS-R), and it stimulates growth hormone (GH) release, food intake and gastrointestinal motility in mammals. Ghrelin has also been identified in the chicken, but this peptide inhibits food intake in the chicken. We examined the effects of ghrelin and related peptides on contractility of the isolated chicken gastrointestinal tract in vitro. Among ghrelin-related peptides examined (1 microM of rat ghrelin, human ghrelin, chicken ghrelin and growth hormone releasing peptide-6 (GHRP-6)), only chicken ghrelin was effective on contraction of the chicken gastrointestinal tract. Des-acyl chicken ghrelin was ineffective, suggesting that octanoylation at Ser3 residue of chicken ghrelin was essential for inducing the contraction. Amplitude of chicken ghrelin-induced contraction was region-specific: highest in the crop and colon, moderate in the esophagus and proventriculus, and weak in the small intestine. The contractile response to chicken ghrelin in the crop was not affected by tetrodotoxin (TTX), but that in the proventriculus was decreased by TTX and atropine to the same extents. D-Lys3-GHRP-6 (a GHS-R antagonist) caused a transient contraction and inhibited the effect of chicken ghrelin without affecting the high-K+-induced contraction. Chicken ghrelin potentiated electrical field stimulation-induced cholinergic contraction without affecting the responsiveness to bath-applied carbachol in the proventriculus. The location of GHS-R differs in the crop (smooth muscle) and proventriculus (smooth muscle and enteric neurons). These results indicate that ghrelin has contractile activity on gastrointestinal tract in the chicken in vitro, and the effect was region-specific. The action would be mediated through the GHS-R, which is highly sensitive to chicken ghrelin.

The motilin pharmacophore in CHO cells expressing the human motilin receptor

We performed a structure-activity study with the human motilin receptor, which was recently cloned from thyroid tissue. N-terminal fragments, Ala-analogs of motilin, and motilides were tested in a cell line that expresses the cloned human motilin receptor and apoaequorin. Full potency to induce calcium fluxes was obtained with N-terminal fragments of 14 amino acids. Motilin fragments 1-14 in which residues 1 (Phe), 4 (Ile), and 7 (Tyr) were replaced by Ala showed the largest reduction in potency. Only motilides with an enol configuration had markedly higher potencies compared to erythromycin A. The potencies to induce Ca(2+) fluxes correlated strongly with rabbit binding and contractility data, suggesting that the cloned receptor is indeed the motilin receptor, responsible for contractile effects. Conservation of the motilin pharmacophore in evolution indicates an important physiological role of motilin.

Potentiation of motilin-induced contraction by nitric oxide synthase inhibition in the isolated chicken gastrointestinal tract

The present experiments were designed to determine whether or not endogenous nitric oxide (NO) modifies the contractile response to chicken motilin (ch-MT) in the gastrointestinal (GI) tract (proventriculus and small intestine) of the chicken. ch-MT (1 nmol L(-1)-1 micromol L(-1)) caused contractions of longitudinal muscle strips of the proventriculus through both myogenic and neurogenic (mostly cholinergic) mechanisms. On the other hand, ch-MT (0.1 nmol L(-1)-100 nmol L(-1)) contracted the small intestine (duodenum, jejunum and ileum) only through a myogenic mechanism. L-Nitroarginine methylester (L-NAME) potentiated, and L-arginine inhibited, the ch-MT- induced contraction without affecting the responsiveness of acetylcholine (ACh) or 5-hydroxytryptamine in the proventriculus. Electrical field stimulation (EFS)- and 1,1-dimethyl-4-phenylpiperazinium (DMPP)- induced contractions were also potentiated by L-NAME. The potentiation by L-NAME was prevented by L-arginine but not by D-arginine. However, in the presence of atropine or tetrodotoxin, neither L-NAME nor L-arginine modified the responses to ch-MT and DMPP. In contrast to the proventriculus, L-NAME and L-arginine were both ineffective in modifying the ch-MT-induced contraction in the small intestine. These results indicate that NO synthase inhibition potentiates the contractile response of ch-MT, EFS and DMPP in the chicken proventriculus through reduction of endogenous NO-mediated presynaptic inhibition on neural ACh release. However, NOS inhibition did not modify the myogenic (direct) action of ch-MT in gastric and intestinal smooth muscles of the chicken.

Demonstration of a functional motilin receptor in TE671 cells from human cerebellum

BACKGROUND

Our laboratory has described the presence of motilin receptors in the rabbit cerebellum. We discovered its presence in the human TE671 cell line, which is of cerebellar origin.

METHODS

Cytosolic Ca(2+) fluxes were monitored on a confocal microscope in cells loaded with Indo-1 and stimulated with motilin under various conditions. Binding studies were performed with 125I-[Nle(13)]porcine motilin. Using primers, PCR for the motilin receptor was performed.

RESULTS

Cells responded to motilin after 45+/-20 s. At different concentrations of motilin (10(-8), 10(-7), 10(-6.5), 10(-6) and 10(-5) M) the percentage of responding cells was 0+/-0, 0.6+/-1.5, 4.9+/-4.7, 21.7+/-15 and 35.7+/-12, respectively. The response was blocked by the motilin antagonists [Phe(3), Nle(13)]po-motilin (0.8+/-1.8%) and GM-109 (0.0+/-0.0%) and mimicked by the agonist ABT-229 (23.6+/-15%). After stimulation with motilin, ABT-229 or [Phe(3),Leu(13)]po-motilin, but not with the antagonist GM-109, cells were desensitized. The response to motilin persisted in Ca(2+)-free solution (22.8+/-14.7%), was not affected by nifedipine (44+/-11%) but was abolished by incubation with thapsigargin (0+/-0%). Neither ryanodine, nor a previous stimulation with caffeine (0+/-0%) in Ca(2+)-free Krebs, nor both could block the response to motilin (28, 32.0+/-5.7, 41.3+/-6.1%, respectively). Binding studies revealed two binding sites for motilin, with a pK(d) of 8.9+/-0.05 and 6.11+/-0.61 (n=4). There were 100 times more low than high affinity receptors per cell. The presence of receptor mRNA was confirmed by PCR.

CONCLUSION

Functional motilin receptors are present in TE671 cells. The response requires intracellular IP(3)-sensitive Ca(2+) stores. These cells may serve as a model of the central motilin receptor.

Contractile effects and intracellular Ca2+ signalling induced by motilin and erythromycin in the circular smooth muscle of human colon

Motilin has excitatory effects on the colon of the rabbit and the dog, but little is known of its effect on the human colon. The aim of this study was to investigate the effects induced by motilin and erythromycin A (EMA) on muscle strips and on single cells from primary cultures from human colon. Isotonic contraction was recorded in circular muscle strips from macroscopically normal resection specimens of patients operated on for colonic neoplasm. Agonist-induced intracellular Ca2+ ([Ca2+]i) signalling was studied in primary cultures of colonic smooth-muscle cells using the ratiometric Ca2+ indicator Indo 1, on a laser-scanning confocal epifluorescence microscope. In circular muscle strips, norleucine13-porcine motilin ([Nle13]-pm)and EMA induced tonic contractions with an EC50 of 92 +/- 21 nmol L(-1) and 31 +/- 16 micromol L(-1), respectively. The maximal contraction was 21 +/- 4% (motilin) and 33 +/- 12% (EMA) of the response to 10(-4) mol L(-1) acetylcholine (ACh). The motilin antagonist OHM-11526 (10(-5.5) mol L(-1)) abolished the effects of both [Nle13]-pm and EMA. Neither tetrodotoxin (10(-5.5) mol L(-1)), L-nitro-D-arginine methyl ester (L-NAME) (10(-3.5) mol L(-1)) nor guanethidine (10(-5) mol L(-1)) interfered with the effects of [Nle13]-pm or EMA. [Nle13]-pm (10(-11)-10(-6) mol L(-1)) induced rises of [Ca2+]i in cultured colonic myocytes. At 10(-6) mol L-1, 94% of the cells responded, and half of the cells responded at 1.4 nmol L(-1) [Nle13]-pm. 81% (35/43) and 95% (75/79) responded to EMA (10(-6) mol L(-1)) and acetylcholine (ACh, 10(-4) mol L(-1)), respectively. The motilin antagonist GM-109 inhibited motilin- and EMA-induced [Ca2+]i rises. In the absence of extracellular Ca2+, only 13% (7/52) of the cells responded to [Nle13]-pm (10(-6) mol L(-1)) vs. 90% (47/52) to ACh (10(-4) mol L(-1)). Motilin and EMA have direct excitatory effects on circular smooth muscle from the human colon and these effects are mediated via a smooth-muscle motilin receptor. These findings suggest that motilin may regulate colonic motility and that motilides may have therapeutic potential for the treatment of colonic hypomotility.

Sequence and characterization of cDNA encoding the motilin precursor from chicken, dog, cow and horse. Evidence of mosaic evolution in prepromotilin

Motilin is involved in the regulation of the fasting motility pattern in man and in dog, but may have a different role in other species. Immunoreactive motilin has been demonstrated in several species, but the sequence is mostly unknown. The aim of this study was to isolate and sequence the cDNA encoding the motilin precursor from several mammalian species and from chicken. Total RNA was isolated from the duodenal mucosa of the chicken, dog, cow and horse. In each case single stranded cDNA was synthesized. Motilin cDNA fragments were amplified by PCR, ligated into a plasmid and cloned. Clones which were positive after screening with an appropriate (32)P-labeled probe were sequenced. The 5'- and 3'-ends were determined by the rapid amplification of cDNA ends (RACE) method. Analysis of the cDNAs revealed an open reading frame coding for 115 (chicken and cow), or 117 (dog and horse) amino acids. It consists of a 25 amino acid signal peptide, motilin itself, and a 68 (chicken and cow) or 70 (dog and horse) amino acid motilin associated peptide (MAP). As in all motilin precursors already sequenced (man, monkey, pig and rabbit), an endoproteinase cleavage site is present at Lys(23)-Lys(24). Comparison of all known sequences shows considerable identity in amino acid and nucleotide sequence of the signal peptide and motilin. However, the MAPs differ not only in length but also, more strongly, in amino acid and nucleotide sequence. Our study demonstrates that the N- and C-terminal regions of the motilin precursor have evolved at different rates, which is evidence for 'mosaic evolution'.

Isolation and sequence of cDNA encoding the motilin precursor from monkey intestine. Demonstration of the motilin precursor in the monkey brain

The motilin precursor cDNA has been isolated and sequenced from a cDNA library prepared from monkey small intestine. The sequence indicates a 345 bp open reading frame, a 63 bp 5' untranslated region and a 154 bp 3' untranslated region. The sequence encodes a 115 amino acid motilin precursor composed of a 25 amino acid signal peptide, the 22 amino acid motilin peptide and a 68 amino acid motilin associated peptide (MAP). Compared with the human motilin precursor cDNA, there are two amino acid substitutions in the signal peptide, one in motilin and four in the MAP. The presence of the motilin precursor in hypothalamus, hippocampus and cerebellum was demonstrated by RT-PCR.

Isolation and sequencing of the cDNA encoding the motilin precursor from sheep intestine

The nucleotide sequence of sheep prepromotilin has been determined from cDNA clones. The nucleotide sequence revealed an open reading frame of 345 nucleotides encoding 115 amino acids. The amino acid sequence deduced from the nucleotide sequence consists of a 25 amino acid signal peptide, followed by the 22 amino acid motilin sequence, an endoproteinase cleavage site (Lys23-Lys24) and a 66 amino acid motilin associated peptide (MAP). Compared with human and pig motilin we observed two substitutions at positions 10 (Leu-->Val) and 19 (Asn-->Tyr). The second one may explain the poor cross-reactivity of ovine motilin with C-terminally directed antibodies against porcine motilin. The sheep motilin precursor exhibits the same structure as the motilin precursors from rabbit, pig and man. However, while there is considerable identity in the amino acid sequences as well as in the nucleotide sequences of the signal peptide and motilin, the MAP strongly differs between the species. This may be a result of 'mosaic evolution' at the molecular level.

Functional characterization of neural and smooth muscle motilin receptors in the chicken proventriculus and ileum

To characterize the motilin receptors present in the chicken, the effects of chicken motilin (Phe-Val-Pro-Phe-Phe-Thr-Gln-Ser-Asp-Ile-Gln-Lys-Met-Gln-Glu-Lys-Glu-Arg -Asn-Lys-Gly-Gln), Leu13 porcine motilin, canine motilin and three erythromycin derivatives (EMA, EM523, GM611) on the contractility of the chicken gastrointestinal (GI) smooth muscles were investigated in vitro and compared with those in the rabbit duodenum. In the proventriculus longitudinal and circular muscle layers, chicken motilin (3 nM-1 microM) caused an atropine- and a tetrodotoxin-sensitive contraction (EC50 = 39-49 nM), and potentiated the EFS-induced contraction without affecting the responsiveness of acetylcholine. EM523 and GM611 (3-100 microM) contracted the proventriculus longitudinal muscle, and the maximum amplitudes of contraction were about 60% of that induced by chicken motilin. Chicken motilin (0.1 nM-100 nM) also caused contraction of the ileum (EC50 = 7 nM) through direct action on the smooth muscle cells. On the other hand, erythromycin derivatives showed only a weak contractile efficacy (about 20% of the maximum response of chicken motilin) even at high concentrations (10-100 microM). The rank order of potency in the ileum was chicken motilin > canine motilin > or = Leu13 porcine motilin > > GM611 > or = EM523 > or = EMA. GM109 slightly inhibited the ideal contractions induced by Leu13 porcine motilin at 100 microM (pA2 = 3.86). In the rabbit duodenum, chicken motilin was a full agonist with the same intrinsic activity as Leu13 porcine motilin, canine motilin and the erythromycin derivatives. However, the rank order of potency (Leu13 porcine motilin > or = canine motilin > chicken motilin > GM611 > or = EM523 > EMA) was different from that in the chicken ileum. In conclusion, chicken motilin causes an excitatory response in the chicken GI tract through activation of neural (proventriculus) and smooth muscle motilin receptors (ileum). The motilin receptor present in the ileum is different from that demonstrated in the rabbit intestine, because of a different rank order of motilin peptides in producing the contraction, low contracting activity of erythromycin derivatives and low antagonistic efficacy of GM109. Different pharmacological characteristics of the mechanical response induced by motilin peptides and erythromycin derivatives between the proventriculus and the ileum are discussed.

Identification of motilin mRNA in the brain of man and rabbit. Conservation of polymorphism of the motilin gene across species

The data regarding the identity of motilin-like immunoreactivity in the central nervous system are controversial. The aim of the present study was to clarify whether motilin mRNA is present in the brain of rabbit and man. Total RNA, prepared from several regions of the rabbit brain, was subjected to RT-PCR aimed at amplifying a 294 bp cDNA fragment of the rabbit motilin precursor. The amplified product was subcloned and sequenced. The sequence showed 7 differences compared to the one reported for the duodenal precursor (1). However the duodenal precursor from the rabbit used in the present study revealed identical substitutions. One of these, involving amino acid -11 of the signal peptide, was shown to be due to gene polymorphism, as has also been described at this site in man. By radioimmunoassay the highest concentration of motilin (fmol/mg protein) was detected in the hippocampus (4788 +/- 295), the lowest in the telencephalon (2127 +/- 221). Using a similar approach, but starting from commercial human brain mRNA, the sequence of a comparable cDNA fragment of the human brain motilin precursor was obtained. Its sequence was identical with the one published for the human intestinal precursor (41). Our study demonstrates that motilin mRNA is present in the brain of man and rabbit. Together with our recent findings of central motilin receptors, they suggest a central role for motilin.

Motilin and clinical application

Motilin is a regulatory polypeptide of 22 amino acid residues and orginates in motilin cells scattered in the duodenal epithelium of most mammals and chickens. Motilin is released into the general circulation at about 100-min intervals during the interdigestive state and is the most important factor in controlling the interdigestive migrating contractions. Recent studies have revealed that motilin stimulates endogenous release of the endocrine pancreas. Clinical application of motilin as a prokinetic has become possible since erythromycin and its derivatives were proved to be nonpeptide motilin agonists.