Canine Motilin Research Articles

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), Leu 13 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 μM) caused an atropine- and a tetrodotoxin-sensitive contraction (EC 50=39–49 nM), and potentiated the EFS-induced contraction without affecting the responsiveness of acetylcholine. EM523 and GM611 (3–100 μM) 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 (EC 50=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 μM). The rank order of potency in the ileum was chicken motilin>canine motilin≥Leu 13 porcine motilin>>GM611≥EM523≥EMA. GM109 slightly inhibited the idea contractions induced by Leu 13 porcine motilin at 100 μM (pA2=3.86). In the rabbit duodenum, chicken motilin was a full agonist with the same intrinsic activity as Leu 13 porcine motilin, canine motilin and the erythromycin derivatives. However, the rank order of potency (Leu 13 porcine motilin≥canine motilin>chicken motilin>GM611≥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.

Demonstration and characterization of motilin-binding sites in the rabbit cerebellum.

This is the first report on central motilin receptors. Autoradiography on cerebellar slices revealed specific motilin-binding sites in the molecular layer of the cortex. Scatchard analysis of cold saturation studies showed the existence of a high-(pKd,hi = 9.07 +/- 0.09, where pKd is the negative logarithm of the dissociation constant) and a low-affinity binding site (pKd,lo = 6.56 +/- 0.09). Similar affinities were found with rabbit motilin and with the porcine (po) antagonist [Phe3, Leu13]po-motilin. Feline and canine motilin had a markedly lower affinity for the low-affinity site (pKd,lo = 5.29 and 4.58, respectively); chicken motilin had a lower affinity for both sites (pKd,hi = 8.36, pKd,lo = 3.97). Erythromycin A and its derivative N-trimethyl erythromycin A cnol ether also bound to cerebellar motilin receptors (pKd,hi = 7.29 and 8.91, respectively). Structure-activity studies with motilin fragments and the potency ranking of agonists suggest that a novel subtype receptor of motilin may exist in the brain. Guanosine 5'-O-(3-thiotriphosphate) (0.1 mM) reduced the number and the affinity for the high-affinity binding sites, which is evidence for G protein-coupled receptors. Our findings open new perspectives for the study of the physiological role of motilin.

EM574, an erythromycin derivative, is a motilin receptor agonist in the rabbit

This study was performed to examine whether an erythromycin derivative, de( N-methyl)- N-isopropyl-8,9-anhydroerythromycin A 6,9-hemiacetal (EM574) is a motilin receptor agonist in the rabbit gastrointestinal tract. EM574 and porcine motilin induced contractions in segments of isolated rabbit intestine with pEC 50 values of 8.26±0.04 and 8.69±0.07, respectively, but not in rat or guinea pig preparations. The sensitivity and efficacy of the response to both compounds in rabbits decreased aborally and was insensitive to pretreatment with atropine or tetrodotoxin, but was markedly suppressed under Ca 2+-free conditions. EM574 and porcine motilin specifically displaced [ 125I-Tyr 23]canine motilin bound to gastric antral smooth muscle homogenates with pIC 50 values of 8.21±0.13 and 9.20±0.11, respectively. The pEC 50 value for the contractile response and pIC 50 value for the receptor binding for motilin, EM574, erythromycin A and three other derivatives correlated well ( r=0.94, P<0.01). Tissue section autoradiography in the antrum revealed that specific labeled motilin binding sites were localized in the circular muscle layer and myenteric plexus, and could be reduced in the presence of an excess of EM574. These results indicate that EM574 is a potent motilin receptor agonist in the rabbit gastrointestinal tract. © 1997 Elsevier Science B.V. All rights reserved.

Exogenous motilin stimulates endogenous release of motilin through cholinergic muscarinic pathways in the dog

BACKGROUND & AIMS: Exogenous motilin is believed to stimulate endogenous release of motilin, but this has not been studied in detail. The aim of this study was to investigate whether and by what mechanism exogenous motilin stimulates endogenous release of motilin in the dog. METHODS: Gastric and duodenal contractile activity in conscious dogs was monitored by chronically implanted force transducers. Plasma canine motilin (c-motilin) concentrations in response to exogenous porcine motilin (p-motilin) were determined by specific radioimmunoassay for c- motilin. The release of motilin from motilin cells obtained from canine duodenal mucosa was studied in vitro using a perifusion system. RESULTS: In vitro, c-motilin release was stimulated by carbachol but not by p-motilin, and the carbachol-induced c-motilin release was inhibited by atropine. In vivo, exogenous p-motilin stimulated endogenous c-motilin release and gastric and duodenal phase III-like contractions; this motilin-induced motilin release was inhibited by atropine, hexamethonium, and a 5-hydroxy-tryptamine 3 receptor antagonist. CONCLUSIONS: In the dog, exogenous motilin stimulates endogenous motilin release through muscarinic receptors on motilin- producing cells via preganglionic pathways involving 5- hydroxytryptamine 3 receptors. (Gastroenterology 1996 Dec;111(6):1456-64)

Excitatory action of [Leu13]motilin on the gastrointestinal smooth muscle isolated from the chicken

The effects of a porcine motilin analogue, [Leu13]motilin (LMT) on the smooth muscle preparations isolated from the chicken gastrointestinal (GI) tract were investigated in vitro. In the proventriculus, LMT (100 nM to 30 microM) caused an atropine-sensitive contraction and enhanced the electrical field stimulation (EFS)- or 1,1-dimethyl-4-phenyl-piperazinium (DMPP)-induced contraction without affecting the response to acetylcholine (ACh). LMT also caused a concentration-dependent contraction of the intestinal tract (duodenum, jejunum, ileum, and colon). The responsiveness to LMT was strongest in the jejunum and weakest in the colon. The responses to LMT in the intestinal segments were not affected by tetrodotoxin, atropine, hexamethonium, pyrilamine, spantide, and 5-hydroxyltryptamine-induced desensitzation, but significantly decreased by verapamil or removal of external Ca2+. LMT did not enhance the EFS- or DMPP-induced contraction in the ileum. Canine motilin also contracted the intestinal segments in a similar concentration range to LMT with an equal potency, but erythromycin A (EMA) and N-ethyl-N-demethyl-8,9-anhydroerythromycin A, 6-9-hemiketal (EM523) showed only a weak contractile activity even at high concentration (up to 100 microM), indicating that motilin receptors in the chicken intestine were somewhat different from those of mammals. In conclusion, LMT produces an excitatory response in the chicken GI tract with a different sensitivity from region to region. The mechanisms of the action were different between the proventriculus and small intestine; that is, LMT contracts the small intestine through the direct action on the smooth muscle cells, but this peptide acts on the enteric cholinergic neurones and stimulates ACh release, and thus regulates autonomic neuroeffector transmission in the proventriculus.

Autoradiographic study of motilin binding sites in the rabbit gastrointestinal tract

Although motilin receptors have been demonstrated by ligand binding studies, there have been no morphological studies of motilin binding site distribution. Light microscopic macro- and micro-autoradiography using highly purified iodinated Tyr 23 canine motilin (10 −10 M) was carried out on the gastric antrum, duodenum, cecum and distal colon of the rabbit. Motilin binding sites were found on the smooth muscle layers of the gastric antrum, duodenum and colon, but no positive binding reaction was detected in that of the cecum. Specific binding sites were particularly abundant in the circular muscle layers, with low concentrations in the longitudinal muscle layers of the gastric antrum, duodenum and colon. No motilin binding sites were found in the mucosa of the gastrointestinal tract and pancreas. The intensity of the positive reaction was inhibited when the tissue was incubated with 10 −8 M unlabeled motilin and was completely abolished by 10 −7 M unlabeled motilin. These results are consistent with the difference in contractile response to motilin between the muscle layers of the gastrointestinal tract.

Biotinyl [formula omitted] motilin as a biologically active receptor probe

The synthesis, purification, and characterization of biotinylated analogues of motilin are reported. The C- terminal of canine motilin was extended by the addition of a cysteine residue, and then biotinylated. Biotinyl motilin was purified by following HPLC and characterized by amino acid analysis. Biotinylation of the ligand was confirmed by ELISA assay with the avidin-biotin system. Biotinyl motilin showed similar affinity for binding to rabbit gastric membrane fraction compared to unlabeled canine motilin, and also retained functional activity in its ability to cause contraction of rabbit duodenal segments. To determine the binding of biotinyl motilin in isolated rabbit antral smooth muscle, cells were incubated with the biotinyl motilin with and without excess of unlabeled motilin. Subsequent addition of avidin-biotinylated peroxidase complex showed the distribution of reaction products over the cell surface. Bioactive biotinyl motilin provides a useful probe for the demonstration of cell surface motilin receptors and will facilitate receptor purification and characterization.

Purification and amino acid sequence of motilin from cat small intestine

Motilin was isolated from cat small intestine by a series of chromatographic steps. Using a radioreceptor assay, based upon binding of iodinated porcine motilin to rabbit antral smooth muscle membranes, it was shown that cat duodenal mucosa contains about 495 ng/g tissue, the jejunal mucosa 161 ng/g tissue and the ileal mucosa 95 ng/g tissue motilin. The duodenal mucosa was extracted with 6% acetic acid and concentrated on a cation exchange Whatman CM-52 gel. After lyophilization the material was further purified by gel filtration (Sephadex G-50), followed by reverse phase (C 18), cation exchange HPLC (Mono S) and three runs on a reverse phase HPLC (Nucleosil 300-5C 18) column. The UV absorbance and the radioreceptor assay were used to monitor the purification. After Mono S chromatography two forms of motilin were detected. The major peak corresponded to a 22 amino acid peptide, which differed only from canine motilin at position 12, where Lys is replaced by Arg. The smaller peak probably corresponds to a deamidated form of this peptide. The sequence homology between cat and porcine/human motilin or cat and rabbit motilin is 81.8% and 72.7%, respectively. The conservation of the first six amino acids in all five species studied is striking, confirming that the biological acitivity of the peptide resides in the N-terminal part.

Mechanism of motilin-induced contractions in isolated perfused canine stomach

Background: Motilin is known to induce gastric phase III contractions via neural pathways in vivo, but the local mechanism of action is not clearly determined. Methods: An isolated perfused canine stomach was used to demonstrate the mechanism of motilin. Synthetic canine motilin at doses of 0.1, 0.3, 1.0, and 3.0 μg/h was infused intra-arterially, and effects of several receptor antagonists on motilin-induced contractions were examined. Results: The immunoreactive motilin concentration of venous effluent showed that motilin at doses of 0.1 and 0.3 μg/h was within the physiological range. Each dose of motilin induced phasic contractions in the isolated stomach, and a dose-related increase in frequency was observed, but not their mean amplitude. Atropine, hexamethonium, ICS205-930, BRL43694, phentolamine, yohimbine, and propranolol significantly inhibited motilin-induced contractions. Naloxone, methysergide, and timolol did not affect the response of motilin. Prazosin significantly increased the mean amplitude of motilin-induced contractions. Conclusions: Physiological dose of motilin can initiate phasic contractions in the stomach independently of the presence of the extrinsic nerves. The results suggest that cholinergic pathway, 5-hydroxytryptamine (HT)3 receptors, and α receptors are involved in the motilin-induced contractions.

Endogenous CCK is not involved in the regulation of interdigestive gastrointestinal and gallbladder motility in conscious dogs

In this study, we assessed whether endogenous CCK is involved in the regulation of interdigestive gastrointestinal and gallbladder motility in conscious dogs with force transducers chronically implanted in the gastric antrum, duodenum, jejunum and gallbladder. L364718 at a dose of 1.0 mg/kg was used as a specific and potent CCK receptor blocker, and its effect on spontaneous interdigestive motility and plasma motilin release were examined. Additionally, the contractile activity of exogenous synthetic canine motilin (20–100 ng/kg) with or without pretreatment with L364718 at a dose of 1.0 mg/kg was assessed. Whether the blocking effect of L364718 on CCK receptors was sufficient or not was verified by giving CCK-OP at a bolus dose of 10 ng/kg. As a result, cyclic changes in interdigestive motor activity and the plasma motilin concentration were not affected by pretreatment with L364718. L364718 also did not affect motilin-induced interdigestive contractile activity in the gastrointestinal tract and gallbladder. On the other hand, the effect of CCK-OP was completely abolished by pretreatment with L364718. It is concluded that endogenous CCK is not involved in the regulation of spontaneous and motilin-induced interdigestive contractions in the canine gastrointestinal tract and gallbladder.

Radioimmunoassay with Heterologous Antibody(Hetero-Antibody RIA): Utilization of Highly Cross-Reactive Antibody Present in Polyclonal Antiserum.

To develop a homologous radioimmunoassay (RIA) for a hormone of a small or rare animal often meets difficulty in collecting a large amount of purified antigen required for antibody production. On the other hand, to employ a heterologous RIA to estimate the hormone often gives poor sensitivity. To overcome this difficulty, a "hetero-antibody" RIA was studied. In a hetero-antibody RIA system, a purified preparation of a hormone is used for radioiodination and standardization and a heterologous antibody to the hormone is used for the first antibody. Canine motilin and rat LH were selected as examples, and anti-porcine motilin and anti-hCG, anti-hCG beta or anti-ovine LH beta was used as the heterologous antibody. The sensitivities of the hetero-antibody RIAs were much higher than those of heterologous RIAs in any case, showing that these hetero-antibody RIA systems were suitable for practical use. To clarify the principle of hetero-antibody RIA, antiserum to porcine motilin was fractionated on an affinity column where canine motilin was immobilized. The fraction bound had greater constants of affinity with both porcine and canine motilins than the rest of the antibody fractions. This fraction also reacted with a synthetic peptide corresponding to the C-terminal sequence common to porcine and canine motilins in a competitive binding test with labeled canine motilin. These results suggest that an antibody population having high affinity and cross-reactivity is present in polyclonal antiserum and indicate that the population can be used in hetero-antibody RIA at an appropriate concentration.

Motilin-Immunoreactive Cells in the Duodenum, Pyloric Stomach and Pancreas of Caimans(Caiman latirostris and Caiman crocodilus, Alligatorinae): A Further Comparison Using Region-Specific Motilin Antisera.

Motilin-immunoreactive cells in the duodenum, pyloric stomach and pancreas of Caiman latirostris and Caiman crocodilus were investigated using region specific antisera for porcine and canine motilin molecules. Motilin-immunoreactive cells were found in the duodenum, pyloric stomach and pancreas of both caiman species. These cells were primarily open-type endocrine ones in the epithelium of the duodenum and pyloric stomach. Motilin-immunoreactive cells were observed in both the exocrine and endocrine portions of the pancreas, and frequently exhibited one or more cytoplasmic processes of variable length. Since motilin-immunoreactive cells do not cross-react with serotonin or any of the other pancreatic and gut hormones, they are considered to be cell type independent from any of the other known pancreatic or gut endocrine cells. The molecular similarity between caiman motilin and porcine and canine motilins and the heterogeneity of the motilin molecule in the caiman digestive system is discussed.

Molecular heterogeneity of human motilinlike immunoreactivity explained by the processing of prepromotilin

Results of studies on the molecular forms of canine motilin suggest that this hormone might be synthesized as a higher molecular weight precursor, as is the case for most other biologically active peptides. Chromatographic analysis of human duodenal mucosa extracts and of human serum, using motilin-specific antibodies, also shows the presence of multiple forms of motilinlike immunoreactivity. Cell free translation of human duodenal messenger ribonucleic acid (mRNA) and immunoprecipitation of nascent peptides with motilin antibodies confirm that motilin is synthesized as a 14–15-kilodalton polypeptide precursor. Sequence of the human intestinal motilin complementary deoxyribonucleic acid (cDNA) demonstrates that this precursor bears a 25-amino acid signal peptide, a single dibasic cleavage site immediately following the 22 amino acids of human motilin, and a 65-amino acid polypeptide (motilin-related peptide) following this dibasic processing site. Southern analysis of human genomic kilobases DNA demonstrates that only one motilin gene is contained within 3.5–4 of human genomic DNA. Northern analysis of human intestinal RNA reveals one species of motilin mRNA of an estimated 700 nucleotides in length. These results suggest that (a) only one gene encodes the synthesis of human motilin in the different tissues where this polypeptide is synthesized; (b) human intestinal motilin is translated from one mRNA species and the resulting precursor is processed within the duodenal mucosa by sequential proteolytic cleavage first at a site within the motilin-related peptide, which results in the liberation of a 6-kilodalton form of motilinlike immunoreactivity, and then at the dibasic amino acid cleavage site, thus freeing motilin 22 from its precursor.

Molecular Heterogeneity of Human Motilinlike Immunoreactivity Explained by the Processing of Prepromotilin

Results of studies on the molecular forms of canine motilin suggest that this hormone might be synthesized as a higher molecular weight precursor, as is the case for most other biologically active peptides. Chromatographic analysis of human duodenal mucosa extracts and of human serum, using motilin-specific antibodies, also shows the presence of multiple forms of motilinlike immunoreactivity. Cell free translation of human duodenal messenger ribonucleic acid (mRNA) and immunoprecipitation of nascent peptides with motilin antibodies confirm that motilin is synthesized as a 14-15-kilodalton polypeptide precursor. Sequence of the human intestinal motilin complementary deoxyribonucleic acid (cDNA) demonstrates that this precursor bears a 25-amino acid signal peptide, a single dibasic cleavage site immediately following the 22 amino acids of human motilin, and a 65-amino acid polypeptide (motilin-related peptide) following this dibasic processing site. Southern analysis of human genomic kilobases DNA demonstrates that only one motilin gene is contained within 3.5-4 of human genomic DNA. Northern analysis of human intestinal RNA reveals one species of motilin mRNA of an estimated 700 nucleotides in length. These results suggest that (a) only one gene encodes the synthesis of human motilin in the different tissues where this polypeptide is synthesized; (b) human intestinal motilin is translated from one mRNA species and the resulting precursor is processed within the duodenal mucosa by sequential proteolytic cleavage first at a site within the motilin-related peptide, which results in the liberation of a 6-kilodalton form of motilinlike immunoreactivity, and then at the dibasic amino acid cleavage site, thus freeing motilin 22 from its precursor.

Comparison of motilin binding to crude homogenates of human and canine gastrointestinal smooth muscle tissue

Pharmacological studies indicate that in man and in rabbit, but not in dog, motilin has a direct influence upon gastrointestinal smooth muscle. In accordance with this hypothesis we have presented direct biochemical evidence for the presence of motilin receptors on rabbit smooth muscle tissue. We have now extended our studies to human and canine tissue. Tissue homogenates were studied in binding experiments with iodinated porcine [Leu 13]motilin and iodinated canine motilin. It was ascertained that the iodination procedure had little effect on the biological activity of the porcine analogue. In the human antrum specific binding of the iodinated porcine analogue was only found in the smooth muscle layer. It was absent in mucosal or serosal preparations. At 30°C and pH 8.0, binding was maximal after 60 min of incubation, and was reversed by the addition of unlabeled porcine motilin. Binding was enhanced in the presence of calcium and magnesium ions. At a concentration of 10 mM MgCl 2, binding was 220% of the binding observed in its absence. Displacement studies with synthetic porcine [Leu 13]motilin or synthetic natural porcine motilin indicated a dissociation constant ( K d) of 3.6 ± 1.6 nM and a maximal binding capacity ( B max) of 77 ± 9 fmol per mg protein. Canine motilin displaced iodinated porcine motilin with an apparent K d of 2.2 ± 0.9 nM. Compared to antral binding, receptor density decreased aborally and orally, and was absent in jejunum and ileum. In dog specific binding could not be demonstrated in antral and duodenal tissue, neither with labeled porcine nor with labeled canine motilin. However, labeled canine motilin was equipotent to labeled porcine motilin in binding studies with human tissue: the dissociation constant was 0.9 ± 0.6 nM. The present studies therefore demonstrate the existence of a specific motilin receptor in the antroduodenal region of the human gut. Apparently, such receptors are not present in the canine gut. Our data support the hypothesis that in the human gastrointestinal tract, the gastroduodenal area is motilin's target region.

Comparative stimulation of motilin duodenal receptor by porcine or canine motilin

Motilins purified from porcine and canine intestine differ in their amino acid composition in positions 7-8-12-13-14. We studied in vitro the contractile response of longitudinal duodenal muscles from various animals (guinea pig, rabbit, dog) to porcine and canine synthetic motilins. Both substances failed to elicit contraction of the guinea pig duodenum but were active and equally potent on rabbit muscle. In dogs, porcine motilin was inactive at the concentrations tested (up to 10−4 M) whereas canine motilin induced duodenal contractions in a doseresponse fashion (mean dose required to induce half-maximal response: 4.82 ± 0.25 × 10−5 M). The contraction generated by synthetic canine motilin (10−5 M) was not influenced by atropine, hexamethonium, tetrodotoxin, naloxone, or sodium nitroprusside (all used at 10−4 M) but was blocked by verapamil (10−4). Our study (a) shows that species-related structural alterations in motilin molecules generate different bioactive capacities in some animal species, (b) suggests that the middle portion of the molecule is important for its bioactive expression, (c) suggests the presence of motilin receptors on canine duodenal muscle, and (d) suggests that an influx of extracellular calcium is involved in the canine duodenal muscle contraction elicited by canine motilin.

Comparison of the biological activity of canine and porcine motilin in rabbit

The biological activity of porcine and canine motilin was studied in rabbits by establishing dose-response curves of both peptides using two different methods. The dissociation constant, obtained from the displacement of iodinated porcine motilin by canine motilin was 0.6 ± 0.3 nM , versus 1.2 ± 0.4 nM for porcine motilin. For the 13-norleucine and 13-leucine analogues of porcine motilin a value of 0.8 ± 0.3 nM was obtained. Both motilins were almost equipotent in stimulating the in vitro contractile response of longitudinal smooth muscle strips: half-maximal effect was achieved at a concentration of 1.0 ± 0.1 nM for canine versus 1.3 ± 0.2 nM for the 13-norleucine analogue of porcine motilin. We conclude that porcine and canine motilin have a comparable bioactivity in the rabbit, although canine motilin is slightly more effective. The motilin receptor is probably specific for the N-terminal portion which is identical in both molecules.

&lt;b&gt;Preparation of iodinated synthetic canine motilin for radioimmunoassay and radioreceptor &lt;/b&gt;&lt;b&gt;assay &lt;/b&gt;

&lt;b&gt;Preparation of iodinated synthetic canine motilin for radioimmunoassay and radioreceptor &lt;/b&gt;&lt;b&gt;assay &lt;/b&gt;

Variations in plasma motilin, somatostatin, and pancreatic polypeptide concentrations and the interdigestive myoelectric complex in dog.

We have looked at the plasma concentrations of motilin, pancreatic polypeptide (PP), and somatostatin (STS) during the various phases of the interdigestive motor complex (IDMC) in dogs. As expected, motilin cyclical increase was always associated with the phase III of the IDMC. Statistical analysis of PP variations revealed a significant rise 10 min before duodenal phase III; however, in individual animals, this relationship was inconsistent. Although a dose-related increase in PP blood levels was induced by administration of synthetic canine motilin (0-200 ng kg-1 iv), fasting plasma levels of PP were not correlated with the concentrations of circulating endogenous motilin. After truncal vagotomy, while motilin release and the intestinal motility pattern remained unaltered, the phase III associated cyclical increases of PP disappeared. Infusion of physiological amounts of PP (1 microgram kg-1 h-1 for 3 h) mimicking the postprandial release failed to reproduce a fed pattern type of intestinal motility and of motilin secretion. No statistical correlation could be established between STS plasma levels and the motor activity of the intestine. STS plasma levels were not correlated with circulating concentrations of motilin and the exogenous administration of physiological doses of synthetic canine motilin failed to modify STS plasma levels. Morphine (200 micrograms kg-1 iv) stimulated only the release of motilin. These data suggest that the role played by circulating concentrations of PP and STS in the control of the IDMC in dog is at most minimal.

Synthesis of canine motilin, a gastric motor activity-stimulating polypeptide, and its N1-substituted analogs.

The docosapeptide corresponding to the entire amino acid sequence of canine motilin, a newly characterized gastric motor activity-stimulating polypeptide, was synthesized by the conventional solution method. All protecting groups employed were removed by 1 M trifluoromethanesulfonic acid-thioanisole-trifluoroacetic acid and the deprotected peptide was purified by gel-filtration on Sephadex G-25, followed by partition chromatography and reverse phase high performance liquid chromatography. When contractile activity on rabbit duodenal muscle was examined, synthetic canine motilin was as active as synthetic porcine motilin. The relative potencies of Lys1 and Ser1 derivatives prepared in the same manner as canine motilin were ca. 1/1000 and 1/250, respectively.