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 pheasant ghrelin and motilin and their actions on contractility of the isolated gastrointestinal tract.

Motilin and ghrelin were identified in the pheasant by molecular cloning, and the actions of both peptides on the contractility of gastrointestinal (GI) strips were examined in vitro. Molecular cloning indicated that the deduced amino acid sequences of the pheasant motilin and ghrelin were a 22-amino acid peptide, FVPFFTQSDIQKMQEKERIKGQ, and a 26-amino acid peptide, GSSFLSPAYKNIQQQKDTRKPTGRLH, respectively. In in vitro studies using pheasant GI strips, chicken motilin caused contraction of the proventriculus and small intestine, whereas the crop and colon were insensitive. Human motilin, but not erythromycin, caused contraction of small intestine. Chicken motilin-induced contractions in the proventriculus and ileum were not inhibited by a mammalian motilin receptor antagonist, GM109. Neither atropine (a cholinergic receptor antagonist) nor tetrodotoxin (a neuron blocker) inhibited the responses of chicken motilin in the ileum but both drugs decreased the responses to motilin in the proventriculus, suggesting that the contractile mechanisms of motilin in the proventriculus was neurogenic, different from that of the small intestine (myogenic). On the other hand, chicken and quail ghrelin did not cause contraction in any regions of pheasant GI tract. Since interaction of ghrelin and motilin has been reported in the house musk shrew, interaction of two peptides was examined. The chicken motilin-induced contractions were not modified by ghrelin, and ghrelin also did not cause any contraction under the presence of motilin, suggesting the absence of interaction in both peptides. In conclusion, both the motilin system and ghrelin system are present in the pheasant. Regulation of GI motility by motilin might be common in avian species. However, absence of ghrelin actions in any GI regions suggests the avian species-related difference in regulation of GI contractility by ghrelin.

Identification, expression analysis, and functional characterization of motilin and its receptor in spotted sea bass (Lateolabrax maculatus).

Motilin (MLN), an interdigestive hormone secreted by endocrine cells of the intestinal mucosa, binds to a G protein-coupled receptor to exert its biological function of regulating gastrointestinal motility. In the present study, we identified the prepromotilin and mln receptor (mlnr) from the spotted sea bass, Lateolabrax maculatus. Mln consisted of an ORF of 336 nucleotides encoding 111 amino acids. The precursor protein contained a 17-amino-acid mature peptide. Mlnr had an ORF of 1089 bp encoding a protein of 362 amino acids. Seven transmembrane domains were predicted with TMHMM analysis. The phylogenetic analysis of mln and mlnr showed that they fell into the same clade with respective counterpart of selected fishes before clustering with other detected vertebrates. Both mln and mlnr genes were highly expressed in intestine of spotted sea bass using quantitative real-time PCR. In situ hybridization indicated that mln and mlnr mRNA were both localized in the lamina propria and the epithelial cell of intestinal villus. The expressions of both genes were regulated under short-term starvation in a time-dependent manner. In vitro experiments indicated that the expressions of ghrelin (ghrl), gastrin (gas) and cholecystokinin (cck) were enhanced by MLN after 3-h treatment, but the effect was absent after 6 or 12-h incubation. Taken together, the MLN and its receptor might play important roles in regulating intestinal motility in spotted sea bass.

Induction of secondary structure in the peptide hormone motilin by interaction with phospholipid vesicles.

Motilin is an intestinal peptide hormone that binds to a membrane bound receptor located in the gut tissue. Circular dichroism (CD) was used to study the interaction between either porcine or rabbit motilin or a 1-16 fragment of porcine motilin, with model systems of lipid membranes: sodium dodecyl sulphate (SDS), 1,2-dioleoyl-sn-glycero-3-phosphoglycerol (DOPG) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The CD measurements show significant induction of secondary structure in both motilins and the fragment when negatively charged vesicles (DOPG) or negatively charged micelles (SDS) were present. In contrast, neutral DOPC vesicles did not induce any change in the secondary structure compared to water, in which a random-like secondary structure dominates. The induced secondary structure in the presence of DOPG vesicles is very close to that induced by a mixed aqueous solution containing 30% hexafluoroisopropanol, in which previous NMR-studies have resulted in a three-dimensional solution structure of porcine motilin. In both porcine and rabbit motilin the alpha-helix content is about 50%. This is in agreement with the presence of an amphipathic helix in the C-terminal half of motilin interacting with phospholipid membranes. The interaction appears to be mainly electrostatic in nature, and does not induce any significant alterations in the vesicle, as monitored by EPR studies of spin labels located at the fifth carbon atom of the backbone in a stearic acid molecule. In the 1-16 fragment the alpha-helical content induced by DOPG and SDS is only about 20%.

The isolation and characterization of rabbit motilin precursor cDNA.

The cDNA sequence of rabbit motilin precursor has been determined. The predicted amino acid sequence indicates that the precursor consists of 133 amino acids and includes a 25 amino acid signal peptide followed by the 22 amino acid motilin sequence and an 86 amino acid motilin associated peptide (MAP). As in the human and porcine precursors, two lysine residues follow motilin in the rabbit sequence. Rabbit motilin shares 64% amino acid sequence identity with human and porcine motilin, and all amino acid substitutions represent conservative changes. Amino acid sequence alignments of the rabbit, human and porcine MAP sequences suggest three functional/structural motifs corresponding to a putative endoproteinase recognition site, a putative PEST site and a potential posttranslational processing recognition element.

Motilin-bicelle interactions: membrane position and translational diffusion.

The interaction between the peptide hormone motilin and bicelles has been investigated by pulsed field gradient-nuclear magnetic resonance methods and by the use of paramagnetic probes. Diffusion coefficients were measured for motilin, the phospholipids with and without motilin, and for tetramethylsilane. The results show that around 90% of motilin is bound to acidic bicelles and 84% of motilin is bound to neutral bicelles. It is found that the apparent bicelle size is reduced by the presence of motilin. This cannot be explained by changes in 1,2-dihexanoyl-sn-glycero-3-phosphatidylcholine solubility. The use of paramagnetic agents to investigate the position of motilin shows that the turn in the N-terminus of motilin is inserted into the bicelle, while the helix most likely resides within the head-group layer.

Identification and expression of the motilin precursor in the guinea pig.

Motilin has never been isolated from rodents, the most frequently used laboratory animals, despite several attempts. We have isolated and sequenced the motilin precursor from duodenal mucosa of guinea pig (GenBank accession number AF323752) and studied its expression in several tissues. The percent homology with human motilin is the lowest yet observed due to several unique substitutions in the C-terminal end. As expected, the precursor was present in the gut mucosa with the exception of the gastric corpus. It was also present in medulla oblongata, nucleus of the solitary tract, hypophysis, spinal cord, hypothalamus, and cerebellum but not in the cerebral cortex. For the first time we demonstrated motilin expression in the thyroid.

The structure of erythromycin enol ether as a model for its activity as a motilide.

Erythromycin enol ether is a potent mimic of the peptide hormone motilin. To understand its biological activity, its three-dimensional structure in CD(2)Cl(2) was determined from constrained molecular mechanics using constraints derived from NMR spectra. The structure of the enol ether is well defined by 10 structures that minimize the energy and satisfy the NMR data. We infer the molecular basis for its activity as a motilide from a comparison of its structure with that of motilin. The macrolide ring of the enol ether is a beta-turn mimic of the peptide. Furthermore, a superposition of the structures of the enol ether and motilin shows a striking overlap of the sugar rings attached to the macrolide ring with essential aromatic side chains in the peptide.

Design and synthesis of motilin antagonists derived from the [1-4] fragment of porcine motilin.

A series of cyclic peptides having the general structure H-Phe-c[-N(epsilon)-Lys-X-NH-(CH(2))(n)-CO-] were designed on the basis of structure-activity relationship studies of motilin. All were motilin antagonists. The cyclic peptides, in which X is a 3-tert-butyl-substituted tyrosine residue (H-Phe-c[-N(epsilon)-Lys-Tyr(3-tBu)-beta Ala-] (3), H-Phe-c[-N(epsilon)-Lys-Tyr(3-tBu)-Gly-] (6), H-Phe-c[-N(epsilon)-Lys-Tyr(3-tBu)-Abu-] (7), and H-Phe-c[-N(epsilon)-Lys-Tyr(3-tBu)-Ahx-] (8)) showed potent motilin receptor antagonistic activity in the rabbit smooth muscle (pA(2) > 7). The 3-tert-butyl Tyr was found to be the moiety responsible for enhanced binding to the motilin receptor, while the size of the ring had little importance.

Identification of cDNA encoding motilin related peptide/ghrelin precursor from dog fundus.

A novel protein expressed by entero-endocrine cells of the mouse stomach was named prepromotilin Related Peptide (ppMTLRP) since it shares sequence similarities with the prepromotilin (Tomasetto et al.). The mouse ppMTLRP was found identical to the rat precursor of ghrelin (ppghrelin), an endogenous ligand specific for the Growth Hormone Secretagogue receptor identified from rat stomach (Kojima et al.). In the present study the cDNA encoding the dog counterpart of ppMTLRP/Ghrelin has been isolated and sequenced. The dog ppMTLRP/Ghrelin cDNA showed scores of respectively 80% and 75% homology with its human and mouse counterparts. By translation of the dog ppMTLRP/Ghrelin cDNA sequences, two ORFs could be deduced encoding either a 117 amino acid ppMTLRP/Ghrelin or the deleted Gln14 ppMTLRP/Ghrelin, as it was also known in mouse, rat and man. The dog ppMTLRP/Ghrelin shared 91% similarity and 78% identity, and 89% similarity and 78% identity with the human and mouse ppMTLRP/Ghrelin proteins respectively. The best score of homology was found in the MTLRP/Ghrelin sequence itself. Indeed the dog MTLRP/Ghrelin peptide shared 100% similarity and 93% identity, and 96% identity and similarity, with the human and mouse MTLRP/Ghrelin. Using Northern blot analysis to study dog ppMTLRP/Ghrelin gene expression on dog adult gut tissues, maximal expression level was found in the stomach fundus and corpus, and no expression could be detected in the stomach antrum nor in the duodenum, jejunum, ileum, colon or liver. In conclusion, we have identified ppMTLRP/Ghrelin from dog, and found that it is highly conserved with man, mouse or rat. The expression pattern along the gastro-intestinal tract is similar to the expression pattern previously described in mouse.

Isolation, sequence, and bioactivity of chicken motilin.

Motilin was isolated from acid extracts of the small intestine of chickens by a combination of gel filtration chromatography, ion-exchange, and reverse-phase HPLC. The purification was monitored using a radioreceptor assay. The sequence of chicken motilin is FVPFFTQSDIQKMQEK-ERNKGQ. Although the six residues differing from porcine motilin (4, 7-10, and 12) are mostly in the pharmacophore of porcine motilin, the affinity of chicken motilin and of the (1-14) fragment of chicken motilin for the motilin receptor of rabbit antral smooth muscle is not much reduced (pKds of 8.90 and 8.45), compared with the affinity of [Nle13]porcine motilin (pKd 9.12). With smooth muscle tissue of the chicken, however, receptors could not be demonstrated with binding studies. In the tissue bath chicken motilin induced a dose-dependent tonic contraction, which was most pronounced with muscle strips prepared from chicken jejunum. This response was blocked by the Ca2+ antagonist verapamil, but atropine, TTX, L-NNA, guanethidine, prazosin, and yohimbine had no effect. The pEC50 for chicken motilin in the chicken jejunum was 7.41. Motilins from other species had lower potencies, and [Phe3, Leu13]porcine motilin, an antagonist in the rabbit, was an agonist in the chicken. The motilin agonists erythromycin A and EM-523 were almost without effect. Tested against rabbit duodenum, chicken motilin had a smaller potency than mammalian motilins. Thus, chicken motilin and the chicken motilin receptor differ from their mammalian counterparts.

Sequence, distribution and quantification of the motilin precursor in the cat.

Due to motilin's relation to the migrating motor complex (MMC), the physiology of motilin has been mostly studied in man and dog. The cat does not have an MMC pattern, and little is known about cat motilin. Therefore we identified the cat motilin precursor (GenBank accession no. AF127917) and developed a quantitative polymerase chain reaction (PCR) to explore its distribution in the gastrointestinal tract and in the central nervous system (CNS). The precursor is closely related to the dog precursor and consists of an open reading frame of 348bp encoding the signal peptide (25 amino acids), the motilin sequence (22 amino acids) and the motilin associated peptide (69 amino acids). One amino acid of the signal peptide was subject to gene polymorphism. Quantification of motilin messenger RNA (mRNA) was for the first time achieved. It is most abundant in the gastrointestinal tract, with the highest concentration in the duodenum, the lowest in the colon and is not detectable in the corpus. However an important expression was also observed in several regions of the CNS, except the striatum and cerebral cortex. The highest level was in the hypothalamus (although 23-fold lower than in the duodenum), the lowest level in the pons. Moderate levels were found in the thyroid. These data suggest that the physiological role of motilin may extend beyond its effect on gastrointestinal motility.

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.

D-amino acid and alanine scans of the bioactive portion of porcine motilin.

A recent systematic study of porcine motilin fragments has clearly shown that biological activity resides in the amino-terminal end. The amino-terminal tetradecapeptide retains more than 90% of the potency of the full molecule. We now examined the effect of replacement of residues 1 through 11 by either their D-isomer or by alanine in [Leu13]pMOT(1-14). Peptides were synthesized using Fmoc solid phase methodology, purified by HPLC, and assayed for their ability to displace bound motilin (rabbit antral smooth muscle homogenate) and to induce contractions (isolated rabbit duodenal segments). The negative logarithm of the concentration displacing 50% of the tracer (pIC50), or producing 50% of the maximal contractile response (pEC50), was determined. All compounds were still full agonists. A reduction in potency of more than two log units was seen for the compounds in which residues 1 (Phe), 4 (Ile), and 7 (Tyr) were replaced by Ala and residues 3 (Pro), 4 (Ile), and 6 (Thr) by their D-isomer. The largest drop was noted for the analogs substituted at position 4. For all compounds there was an almost perfect correlation between the pIC50 and the pEC50 values (r = 0.96), although the pEC50 was consistently smaller. These results show that the biological activity of motilin is mainly determined by the first seven residues. The pharmacophore consists of the aromatic rings from Phe1 and Tyr7 and the aliphatic side chains from Val2 and Ile4. Pro3, Phe5, and Thr6 may stabilize the bioactive conformation.

Purification and amino acid sequence of human motilin isolated from a motilin containing liver metastasis.

The acid extract of a liver metastasis from a patient with elevated plasma motilin levels contained large quantities of motilin (3.37 micrograms/ml). The extract was concentrated on a C18-column and motilin was isolated by gel chromatography (Sephadex G-50) followed by cation ion exchange chromatography (HR5/5 Mono-S) and three successive steps of reverse phase chromatography (Nucleosil 300-5 C18). The pure peptide was sequenced and the identity of porcine and human motilin was confirmed. This is the first report of a tumor containing large amounts of motilin.

Structure and dynamics of motilin. Time-resolved fluorescence of peptide hormone with single tyrosine residue.

Time-resolved fluorescence and CD spectroscopy were used to characterize the structure and dynamics of the peptide hormone motilin with a single tyrosine residue among its 22 amino acids. CD spectroscopy showed that secondary structure is independent of concentration in the range 1 x 10(-5)-2.6 x 10(-4) M, and of the presence of DOPC lipid vesicles, but is strongly induced by addition of hexafluoroisopropanol. The fluorescence studies with tyrosine as the intrinsic fluorophore, performed at the MAX synchrotron laboratory at Lund, showed that three fluorescence lifetimes (0.4 ns, 1.7 ns and 3.6 ns at 20 degrees C) and two rotational correlation times (0.4 ns and 5 ns at 20 degrees C) were needed to account for the data. The different decay times are interpreted as representing ground-state rotamers interconverting slowly on the ns time scale. The rotational correlation times are ascribed to local angular motion of the tyrosyl ring, and global motion of the whole peptide, respectively.

A study of melittin, motilin and galanin in reversed micellar environments, using circular dichroism spectroscopy.

Circular dichroism spectroscopy has been used to study the behaviour of the cytolytic peptide melittin, the intestinal peptide hormone motilin (porcine) and the neuropeptide galanin (porcine) in various reversed micellar systems. The micellar systems used contained sodium dodecyl sulphate, bis(2-ethylhexyl) sulfosuccinate, n-dodecyltrimethylammonium chloride or polyoxyethylene(7) lauryl ether. Various structural changes of the peptides, induced either by varying the water content or the surface charge of the reversed micelles, could be monitored. Melittin has in all micellar systems a large amount of alpha-helix, and is almost unaffected by both water content and the surface charge of the reversed micelles. Motilin on the other hand attains an alpha-helical structure at low water content only. The surface charges seem to be of importance for the association between motilin and the hydrated reversed micellar surface. Galanin has the most complicated behaviour with a large dependence on surface charge and with a water content dependence which varies with the surfactant used. Stabilization of alpha-helical secondary structures was only seen in negatively charged reversed micelles. These observations indicate a specific interaction between galanin and surfactant, probably of electrostatic nature.

Motilin in human milk: identification and stability during digestion.

The presence of motilin in human milk and the influence of human milk on the degradation of [125I][Nle13] porcine motilin by gastric and duodenal fluids were investigated. Milk and plasma samples were collected from 14 mothers, and motilin was measured by radioimmunoassay. Plasma levels were 416 +/- 37 pg/mL. In 8 defatted samples the motilin level was 105 +/- 14 pg/mL, in the six others levels were above 1000 pg/mL but dilution curves were non-linear. After solid-phase extraction milk levels were 108 +/- 21 pg/mL in 13 samples, in 1 sample the dilution curve was still non-linear. The stability of motilin after ingestion was studied in vitro by incubating [121I][Nle13] porcine motilin with gastric and intestinal juices obtained from newborns (10 times diluted). Incubations were performed at 37 degrees C at pH 1.8, 3.2 and 5.8 for the gastric fluid and at pH 7.4 for the duodenal fluid. After different times of intervals (5, 10, 20 and 30 minutes) intact motilin was precipitated with trichloroacetic acid and the radioactivity of the supernatant was determined. Motilin was rapidly degraded by gastric juice. The breakdown was greatest at pH 3.2 (74% after 30 minutes) and lowest at pH 5.8 (29%), the pH after milk feeding in neonates. Degradation by intestinal juice at pH 7.4 was also very rapid (77% after 30 minutes). Human milk and BSA inhibited partially the gastric digestion at pH 3.2 (17 and 29%, respectively). Digestion by intestinal juice was not affected by human milk and BSA. These results suggest that digestion of motilin in the stomach may be sufficiently retarded by human milk in the newborn to exert a biological role.

Motilin and motilin receptors: characterization and functional significance.

In order to get more insight into the mechanism of action of the gastrointestinal peptide, motilin, and its role in human physiology, we aimed at characterizing motilin and motilin receptors. Motilin. Sequence analysis of the motilin precursor from several species indicated that the N- and C-terminal regions of the motilin precursor have evolved at different rates. Sequence analysis of the motilin precursor in brain tissue of rabbit and man and motilin radioimmunoassay on tissue extracts, proved that motilin is a brain-gut peptide. Plasma motilin levels are increased in patients with ulcerative colitis or Crohn's disease. A weak correlation between the motilin genotype and the susceptibility to inflammatory bowel disease was demonstrated. Motilin receptors. Motilin receptors are expressed early postnatally and can be regulated by changes in its plasma level. The pharmacophore of motilin consists of the aromatic rings from Phe1 and Tyr7 and the aliphatic side chains from Val2 and Ile4. In vivo and in vitro studies showed that in the rabbit and human antrum, smooth muscle and neuronal motilin receptors exist which have different characteristics. In the rabbit duodenum motilin's action depends upon the influx of extra- and intracellular Ca2+. Nevertheless, in primary smooth muscle cultures, Ca2+ influx through L-type Ca2+ channels is the major transduction mechanism. The existence of central motilin receptors was demonstrated by autoradiography. Receptor binding studies allowed the identification of two binding sites. In contrast to antral smooth muscle cells, the response to motilin in the human TE671 medulloblastoma cell line, expressing the motilin receptor, relies on intracellular IP3-sensitive Ca2+ stores. The antibiotic erythromycin-A (EM-A) binds to the motilin receptor and induces contractions with the same regional and species specificity as motilin. This interaction was supported by the discovery of motilin antagonists. Structure activity studies led to the development of more powerful erythromycin derivatives, which lack antibiotic properties and which are now in clinical trial for treatment of hypomotility disorders. Conclusion and perspectives. The physiological role of motilin and its receptors in the brain requires further investigation. Erythromycin and its derivatives act as motilin agonists with clinically useful prokinetic potential. The motilin receptor has recently been cloned and has substantial structural homology with the growth hormone secretagogue receptor. This may not only lead to the further characterization of motilin receptor subtypes and aid the development of safe and selective motilin receptor agonists and antagonists, useful for the treatment of GI disorders, but may also give a new dimension to the role of motilin in human physiology.

A new strategy for metabolic stabilization of motilin using the C-terminal part of ghrelin.

Ghrelin consists of 28 amino acid residues with an octanoyl modification at the third serine residue. Recently we have found that the C-terminal part of ghrelin protects the ester bond of 3-octanoyled serine from plasma esterases and plays the essential role to prolong the plasma half-life and to show its biological activity in vivo. In the present study, we researched whether the C-terminal part of ghrelin has a potential to prolong the plasma half-life of motilin, by comparing the pharmacokinetics of various chimeric peptides of ghrelin and motilin. Motilin is another gastro-intestinal peptide hormone related with ghrelin structurally, binding to the same family of G protein-coupled receptors. Chimeric peptides were designed to be composed of motilin(1-12) fragment, the active core binding to the motilin receptor, GPR38, and C-terminal part of ghrelin. The modification of motilin(1-12) fragment by C-terminal part of ghrelin hardly influenced its agonist activity to GPR38 and almost all these chimeric peptides showed more than two times longer plasma half-lives than motilin in rats. From the relationship between structures of chimeric peptides and their corresponding plasma half-lives, the mid-region of ghrelin rich in basic amino acids ((15)RKESKK(20)) was considered to be the most important in prolonging the plasma half-life of motilin. The deletion of these fragments or replacement of 17th glutamic acid with a neutral amino acid resulted in short plasma half-lives. In conclusion, our data suggested that the C-terminal part of ghrelin has a potential to improve the biokinetics of motilin probably by a metabolic stabilizing effect.