Effect of synthetic motilin and related polypeptides on contraction of gastrointestinal smooth muscle

Comparison of the gastroprokinetic effects of ghrelin, GHRP-6 and motilin in rats in vivo and in vitro

Ghrelin and motilin form a new family of structurally related peptides. We compared the gastroprokinetic effects of ghrelin, the ghrelin receptor agonist, growth hormone releasing peptide 6 (GHRP-6), and motilin in rats in vivo and in vitro.

METHODS

Ghrelin, GHRP-6 or motilin (10-150 microg/kg) were injected i.p. and the effects on gastric emptying and transit were measured after intragastric application of Evans blue. In antral and fundic strips the effect of motilin, ghrelin or GHRP-6 was studied during electrical field stimulation (EFS) in the absence and presence of N(G)-nitro-l-arginine methyl ester hydrochloride (l-NAME) (300 microM).

RESULTS

Ghrelin and GHRP-6 but not motilin accelerated gastric emptying and transit in rats. Ghrelin was more potent than GHRP-6 and the dose-response relationship for ghrelin but not for GHRP-6 was bell-shaped. In fundic or antral strips, neural responses to EFS consisted of an on-relaxation that was reversed into a cholinergically mediated contraction by addition of the nitric oxide (NO)-synthase blocker, l-NAME. The post-stimulus off-contraction was cholinergically mediated. Under normal conditions, the ghrelin agonists reduced the on-relaxations in fundic strips and increased the cholinergic off-contractions in antral and fundic strips. The concentration response curves in muscle strips of the fundus were bell-shaped with maximal effects for ghrelin at 1.2 microM (on-responses) and 0.66 microM (off-responses) and for GHRP-6 at 0.50 microM (on-responses) and 0.26 microM (off-responses). No effects were observed with motilin between 1 nM and 0.1 microM. Studies in the presence of l-NAME confirmed the effect of the ghrelin agonists on cholinergic excitatory motor responses. No effects were observed with motilin under the different experimental conditions. The presence of growth hormone secretagogue receptor 1a transcripts in the strip preparations was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR).

CONCLUSION

Ghrelin and GHRP-6 but not motilin accelerate gastric emptying and transit by activating cholinergic excitatory pathways in the enteric nervous system in addition to the known vagal pathways.

Effects of SK-896, a new human motilin analogue ([Leu13]motilin-Hse), on postoperative ileus in dogs after laparotomy

The effects of SK-896, a new human motilin analogue ([Leu13]motilin-Hse), on digestive tract motility in postoperative ileus were evaluated in a dog model of ileus after laparotomy. SK-896 was intravenously administered at 0.17, 0.33 and 0.67 microg/kg starting soon after operation and then at 6-h intervals, for a total of 9 times. SK-896 progressively, dose-dependently and significantly increased the duodenal motility from 1 h after operation. The recovery time of the gastrointestinal-interdigestive migrating complex (GI-IMC) activity, which is an indicator of normal gastrointestinal tract activity after laparotomy, was 56.5 +/- 5.0 h in the control group. SK-896 significantly shortened this recovery time. On the other hand, the plasma SK-896 concentrations declined diexponentially after administration, and can be described by a linear pharmacokinetic model within the dose range used. In addition, the pharmacokinetics of SK-896 did not change significantly at any postoperative time. There was no correlation between the plasma SK-896 concentrations and the intensity of duodenal motility, because the activity in the duodenum decreased transiently 13 h after laparotomy and increased with time thereafter. The changes in the activity are considered to reflect the progressive changes in the state of ileus. In conclusion, SK-896 increased the duodenal motility significantly, shortening the recovery time of GI-IMC-like activity in dogs with post-laparotomy ileus. Therefore, it is expected from these results that SK-896 would be useful and effective for the treatment of gastroparalysis after abdominal surgery.

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.

Identification of the motilide pharmacophores using quantitative structure activity relationships

Erythromycin A and some derivatives have been shown to act as agonists at the motilin receptor site (motilides) and a structural similarity between these molecules and the N-terminal fragment of motilin has been proposed. Conformational analysis and three-dimensional quantitative structure-activity relationship (3D-QSAR) methods have been used to determine the homology between a series of erythromycin A derivatives and motilin 1-10. A total of 18 compounds has been studied to correlate the gastrointestinal motor stimulating (GMS) activity with the structure-related parameters determined by 3D-QSAR. Two models with good predictive power of the GMS activity are presented, leading to the prediction of motilin 1-10 activity. The models are consistent with the majority of the data available. The most significant parameters for GMS activity are a favorable dispersion interaction from the quaternary ammonium group of the desosamine ring. In motilin 1-10, the aromatic side chains of Phe1 and Tyr7 seem to play the same role as the quaternary ammonium group in models 1 and 2, respectively. Some hydroxyl groups of erythromycin A derivatives and hydrophobic groups of the Val2 and lle4 side chains of motilin also contribute to the GMS activity. The experimental GMS activities measured are in good agreement with the predicted values, with correlation coefficient values of 0.98 and 0.94 in models 1 and 2, respectively.

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.

Does motilin stimulate the gastrointestinal motility of the pig? In vitro study using smooth muscle strips and dispersed muscle cells

To clarify the physiological role of motilin in the pig gastrointestinal (GI) tract, effect of Leu13-porcine motilin (LMT) on the contractility of GI smooth muscle was investigated in studies using isolated muscle strips and dispersed muscle cells. LMT produced no contraction in either longitudinal muscle (LM) or circular muscle (CM) of the stomach (fundus, corpus, antrum), duodenum, ileum and colon even at 1 microM. Pretreatment with LMT (1 nM-1 microM) did not potentiate the contractile response to acetylcholine (ACh) in each muscle strip. Dispersed cells from the duodenum responded to ACh in a concentration-dependent manner (EC50 = 10 pM), but not to LMT even at a high concentration (10 microM). Electrical field stimulation (EFS) caused a frequency-dependent (0.2-10 Hz) contraction of the duodenal LM that was almost completely inhibited by atropine or tetrodotoxin. EFS caused the relaxation of duodenal CM in a frequency-dependent manner (0.1-10 Hz). This relaxation was not inhibited by atropine, propranolol, phentolamine or guanethidine, indicating the involvement of noncholinergic, nonadrenergic (NCNA) nerves. NG-nitro L-arginine methylester (L-NAME, 100 microM) attenuated the EFS-induced relaxation and the inhibition at low frequency was larger than that at high frequency. L-Arginine prevented the inhibition by L-NAME but D-arginine did not. LMT (1 nM-1 microM) had no influence on EFS-induced cholinergic contraction of LM and EFS-induced NCNA relaxation of CM layer. The present in vitro studies indicate that motilin is ineffective in producing contraction and in modulating the autonomic neuroeffector transmission of the pig GI smooth muscle, and suggest that pig GI smooth muscle lacks functional motilin receptors.

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.

Structural effects of the selective reduction of amide carbonyl groups in motilin 1-12 as determined by nuclear magnetic resonance

Motilin is a 22-residue peptide stimulating stomach and intestinal motility. The motilin 1-12 fragment displays biological effects similar to the native peptide. Selective reduction of the amide carbonyl groups to form CH2NH analogs leads to a significant reduction in activity for the first two N-terminal positions and to a complete loss of activity for all other positions. The structures of motilin 1-12 and ten reduced analogs were investigated using the temperature dependence of the amide NH chemical shifts. In all the analogs, the structure of the N-terminal region (residues 1-5) was different from the structure of motilin 1-12, which is characterized by hydrogen bonding between Phe1 and Ile4. The structure of the C-terminal region of analogs was similar to the structure of motilin 1-12 for the first two reduction positions only (1-2 and 2-3), indicating that the C-terminal portion of motilin 1-12 is more critical for biological activity. Complete structural characterizations of motilin 1-12, [CH2NH]1-2, and [CH2NH]4-5-motilin 1-12 were performed by two-dimensional NMR spectroscopy and molecular modeling. The structural features observed confirm the differences based on the temperature dependence of the amide NH chemical shifts. These results demonstrate that conservation of the amide bond rigidity is essential for the activity of non-hydrolyzable analogs.

Antagonistic properties of [Phe3,Leu13]porcine motilin

We describe the antagonistic properties due to the replacement of Pro3 by phenylalanine in porcine motilin. The analogue, [Phe3,Leu13] porcine motilin (OHM-11526), displaces iodinated [Nle13]porcine motilin bound to a homogenate of rabbit antral smooth muscle tissue. The dissociation constant (pKd) was 9.26 +/- 0.04, versus 9.11 +/- 0.01 for motilin and 8.24 +/- 0.06 for ANQ-11125, the (1-14) fragment of OHM-11526. The Hill coefficient was close to one and Schild plot analysis confirmed the competitive nature of the interaction. In the tissue bath OHM-11526 was unable to induce contractions of segments of rabbit duodenum. At a concentration of 10(-6) M, OHM-11526 was unable to induce contractions of segments of rabbit duodenum. At a concentration of 10(-6) M, OHM-11526 inhibited the effect of maximally effective doses of porcine motilin and of the erythromycin derivative, EM-523, but was without effect on contractions induced by acetylcholine, substance P and serotonin. Increasing doses of OHM-11526 shifted the dose-response curves of motilin and EM-523 to the right, but caused a depression of the maximal response as well. From the motilin curves, and assuming a dual competitive and non-competitive interaction, the pA2 was 7.79 +/- 0.08, the pD'2 6.91 +/- 0.08. The EM-523 curves yielded comparable data (pA2 = 8.10 +/- 0.12 and pD'2 = 7.06 +/- 0.13). OHM-11526 also blocked the motilin responses observed with smooth muscle strips from the rabbit and human antrum. However, in a preparation of the chicken small intestine, OHM-11526 was a full agonist with a potency (pD2 = 6.84) comparable to that of porcine motilin (pD2 = 6.71). Our data confirm the interaction of motilides with the motilin receptor. Due to its increased affinity for the motilin receptor, OHM-11526 will be a valuable took for studying the physiology of motilin and the pharmacology of motilin and motilides.

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.

Stimulating action of KW-5139 (Leu13-motilin) on gastrointestinal motility in the rabbit

1. The gastrointestinal motor stimulating action of the motilin analogue, KW-5139 (Leu13-motilin), was investigated both in the anaesthetized rabbit and in rabbit isolated smooth muscle tissues. 2. KW-5139 (0.3-10 micrograms kg-1, i.v.) produced motor stimulating actions in the gastric antrum, ileum and descending colon, the excitatory responses of which were initiated at the same time but declined with different time courses. The rank order of the excitatory response was: descending colon > or = gastric antrum >> ileum. 3. Atropine (1-3 mg kg-1, i.v.) or naloxone (1 mg kg-1, i.v.) completely suppressed the excitatory response to KW-5139 in the gastric antrum, but only partially attenuated that in the descending colon. This suggests that the mechanism of the excitatory response is different in the gastric antrum and the descending colon, and that cholinergic neural pathway is involved in the response of the gastric antrum. 4. KW-5139 (0.1 nM-1 microM) caused concentration-dependent contractions of the gastric antrum, duodenum, jejunum, ileum and the descending colon in vitro. In the rabbit intestine, the contractile response to KW-5139 was strongest in the duodenum and weakest in the ileum. 5. The contractile response to KW-5139 in the intestinal segments were not affected by tetrodotoxin, but were decreased by verapamil, or pretreatment with a high concentration of porcine motilin, confirming the involvement of motilin receptors in the response to KW-5139. 6. The present results suggest that the rabbit is a suitable species for the investigation of motilin on gut motility, because of the high responsiveness of the descending colon as well as the upper gastrointestinal tract.

Distribution and characterization of motilin receptors in the cat

We demonstrate binding of [125I][Nle13-po]motilin to homogenates of cat gastric and small intestinal, but not to colonic smooth muscle tissue. The density was (Bmax in fmol/mg protein): 0 (fundus); 12 +/- 2 (corpus); 22 +/- 3 (antrum); 55 +/- 12 (duodenum); 44 +/- 10 (jejunum); 17 +/- 1 (ileum); 0 (colon). A significant (p < 0.05) difference was found between the dissociation constant for motilin in the stomach (pKd = 8.84 +/- 0.06) and in the small intestine (pKd = 8.58 +/- 0.08). The motilides erythromycin-A (EM-A), EM-523, and EM-A N-oxide displaced labeled [Nle13-po]motilin bound to cat duodenal receptor with potencies (pKd) of 5.47 +/- 0.23, 7.60 +/- 0.24, and < 4.3, respectively. Studies with [Leu13-po]motilin fragments showed that the N-terminus of motilin interacts with the receptor. In the tissue bath, duodenal strips mounted in the longitudinal direction responded to motilin, EM-523, and EM-A (pEC50: 8.29 +/- 0.08; 7.12 +/- 0.12; 5.99 +/- 0.15). The compounds had a comparable intrinsic activity (83 +/- 3%; 80 +/- 5%; 82 +/- 5% of the response to ACh), which was unaffected by atropine, TTX, hexamethonium, and zacopride but reduced by verapamil and calcium-free medium. Cat stomach and small intestine possess smooth muscle motilin receptors, which have comparable properties as those found in man and in rabbit.

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 micrograms/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 microgram/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 alpha receptors are involved in the motilin-induced contractions.

Mechanism of gastroprokinetic effect of EM523, an erythromycin derivative, in dogs

BACKGROUND

The pharmacological properties of EM523, a nonpeptide motilin agonist, have not been well characterized.

METHODS

The prokinetic effect of EM523 on motor-stimulating activity in the stomach, duodenum, and jejunum in seventeen conscious dogs was studied using force transducers implanted long term. EM523 (0.3-10.0 micrograms/kg) and receptor antagonists were injected intravenously during the interdigestive state.

RESULTS

EM523 induced phase III-like contractions in a dose-dependent manner, and the contractions were inhibited dose dependently by pretreatment with cholinergic and 5-HT3 receptor antagonists and dopamine but not by adrenoceptor and opiate antagonists or methysergide. The plasma immunoreactive motilin level was increased after EM523 to 60% of the mean maximum value during the spontaneous phase III contractions. Pretreatment with anti-canine motilin serum inhibited EM523-induced contractions by 19.2% in the motor index, but the contractile pattern was not affected.

CONCLUSIONS

EM-523-induced phase III-like contractions are brought about through the cholinergic neural pathway and 5-HT3 receptors, and endogenous motilin release is partially involved.

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.

Synthesis and in vitro evaluation of [Leu13]porcine motilin fragments

Several peptide fragments representing N-terminal, C-terminal, and internal sequences of [Leu13]porcine motilin ([Leu13]pMOT) were synthesized using Fmoc solid phase methodology. Peptides were assayed for motilin receptor binding activity in a rabbit antrum smooth muscle preparation and for stimulation of contractile activity in segments of rabbit duodenum. In vitro activity was directly correlated with motilin receptor binding affinity for all [Leu13]pMOT fragments examined. N-Terminal fragments of just over half the length of the native peptide are nearly equipotent as full-length motilin. These results suggest that the N-terminal segment, together with residues from the mid-portion of the molecule, constitutes the bioactive portion of pMOT. The C-terminal segment, in contrast, contributes little to receptor binding affinity or in vitro activity.

N-terminal portion of motilin determines its biological activity

This study aimed to identify the portion of the 22 amino acid sequence of motilin responsible for the biological activity of the peptide. The contraction of rabbit duodenal muscle in vitro was measured when exposed to synthetic fragments of motilin corresponding to various sequences of the C- or N-terminal portions of the molecule. Fragments 2-22 or 3-22 (where the initial amino acids of the N-terminal ending were removed) were more than 1000 times less potent than the native molecule 1-22. Fragment 1-9 (where the last 13 amino acids located at the C-terminal side of motilin were removed) was devoid of any contractile capacity, while synthetic fragments whose C-terminal structure extended beyond the 1-9 motilin sequence maintained almost complete biological activity. N-terminal amino acid sequence 1-9 is therefore an essential determinant of the contractile activity of motilin.

Direct effects of motilin on isolated smooth muscle from various regions of the human stomach

The effects of motilin on gastrointestinal muscles show great variations in different organs and different species. For a precise regional differentiation, we recorded the mechanical activity of longitudinal and circular strips from fundus, corpus and antrum and of circular preparations from the inner and outer layer of the pyloric sphincter and from the duodenum (20 human stomachs). Motilin produced excitatory effects on the mechanical activity of the circular muscle strips from all regions of the human stomach including the pylorus. The effects on longitudinal preparations and on duodenal strips were weak. The most striking effect was an increase of phasic activity (amplitude) in circular antrum preparations, which exceeded the acetylcholine- and bombesin-induced activity. In pylorus preparations, a strong stimulation of phasic activity was observed with a transition to tonic activity in the inner layer of the pyloric ring at high motilin concentrations. The motilin-induced activity of the pyloric preparations was greater than the acetylcholine-induced contractions and even exceeded the bombesin-induced responses in the outer pylorus. The responses of the muscle strips of the proximal stomach (fundus and corpus) were weaker and did not exceed the acetylcholine-induced activity. All effects remained unaltered by atropine and tetrodotoxin application. The study confirms that motilin can interact directly with the smooth muscle of human stomach.

Current contributions of peptide synthesis to studies on brain-gut-skin triangle peptides

The usefulness of a strong acid, such as MSA or TFMSA/TFA, as a deprotecting reagent in peptide synthesis was examined. By synthesizing several structurally related brain-gut-skin triangle peptides, a number of advantageous features of the thioanisole-mediated deprotecting procedure were demonstrated. New amino acid derivatives, Arg(Mts), Trp(Mts) and Asp(OChp), were introduced to improve the synthetic methodology of complex peptides and the superior properties of Cys(Ad) were evaluated.

Motilin--an update

Motilin isolated in 1971 from the porcine gastrointestinal tract and localized there to endocrine cells, now appears to have a CNS neural origin by RIA and immunohistochemistry. In most species motilin releases neurotransmitters in the CNS to both increase and decrease neural transmission and in the gastrointestinal tract to increase motor activity. In the fasting animal, motilin initiates premature activity fronts of the migrating motor complex (MMC) in the upper gastrointestinal tract by an atropine or tetrodotoxin-sensitive mechanism. Immunoreactive motilin-release from the gut can be correlated with the passage of these fronts through the upper gut. In the dog, the associated events of this MMC, i.e. motor activity of the duodenum extrinsic and intrinsic neural activity and emptying of biliary and pancreatic secretions into the duodenum, all appear to contribute to the peaks in peripheral plasma immunoreactive motilin concentrations. In man, there appears to be a close association of motilin secretion with biliary and pancreatic secretions being emptied into the duodenum and less evidence for motor activity releasing motilin. Only in the dog is there strong evidence for an absolute requirement of motilin for the consolidation of the motor activity of the upper gut into the MMC. In man, the evidence is less convincing although motilin may facilitate the process and in the pig, motilin appears to have little or no role in MMC generation. No pathological consequences of hypermotilemia have been described although elevated motilin levels have been found to be associated with some diarrheal states, renal failure, and in the first week following abdominal surgery. Motilin thus remains a hormone seeking a physiological function in some species and a pathological role in all species.

Neural and humoral factors in postoperative ileus

Two inhibitory mechanisms in the human colon which may contribute to postoperative ileus have been studied. Dopamine, a possible peripheral neurotransmitter, inhibited isolated colonic smooth muscle strips by a direct effect in longitudinal muscle any by a nerve-mediated mechanism as circular muscle. Plasma motilin levels were suppressed pre- and per- operatively and elevation of levels postoperatively correlated with the return of normal motility and the severity of the operation.