- Email: [email protected]
Motilin--an update
Life Sciences, Vol. 35, pp. 695-706, Printed in the U.S.A.
Pergamon Press
MINIREVIEW MOTILI N--AN UPDATE J.E.T. Fox School of Nursing and Department of Neurosciences, McMaster University Hamilton, Ontario, Canada LSN 3Z5
Summ sr y 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 immtmoreactive 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. The search by J.C. Brown for duodenal factors which stimulate canine gastric motility following duodenal alkalinization culminated in the isolation, sequencing, and synthesis of the 22 amino acid peptide porcine motilin (1,2,3,4). It is this peptide (both synthetic and natural) which has been used to study the action of motilin and to develop antibodies for radioimmunoassay (RIA) and immunohistochemical (IHC) studies. This may have led to much of the controversy relating to the origin, action, and release of motilin since relevant studies have rarely been made in the pig. The only other motilin which has been isolated, but not yet synthesized, canine motilin, differs in at least 5 of the 22 amino acids (5) and may be regulated and function differently. The present review will deal with recent findings on the localization of motilin, its sites and mechanisms of action, the mechanisms of its release, the relationship of motilin to the migrating motor complex (MMC), and to pathological conditions. The reader is directed to the reviews by Domsehke (6), 0024-3205/84 $3.00 + .00 Copyright (c) 1984 Pergamon Press Ltd.
696
Motilin -- an Update
Vol. 35, No. 7, 1984
Brown and Dryburg (7), McIntosh and Brown (8), Christofides and Bloom (9), Itch (I0), and Wingate (11), as well as the Proceedings of the Erlangen Symposium on Motilin (12) for an analysis of earlier studies. Localization The controversy concerning whether the gut endocrine cell containing motilin is mainly an enterochromaffin (EC) cell containing serotonin (13,14) or a different non-serotonin containing cell (15,16) r e m ~ n s unsettled. The different findings have been attributed to different antisera (17), to different stages of maturation of the EC cell and hence, differing serotonin content (18) and to heterogeneity of the motilin molecule (19,20,21). Yanaihara et al. (22) ~ r s t suggested that motilin or a motilin-like material might also have a neural origin since extracts of central nervous system revealed a high level of immunoreactive (I) motilin. Extracts of canine and opossum gut muscle layers separated from the mucosa also revealed high I-motilin levels. The highest content in either species was found in the jejunum as compared to the ileum, duodenum, or stomach. These results suggest a neural origin in the gut with a similar overall distribution as endocrine cell I-motilin (23), as well as in the CNS. To date, the only reported localization in nerves by imm~mohistochemistry is in the CNS of the rat. Motilin-like material appeared to be localized in fore brain structures and Purkinje cells of the cerebellum (24,25,26). However, in these studies, most motilin antibodies failed to recognize the motilin-like material in Purkinje cells. Initial biochemical analysis of the motilin-like material f~om whole rat brain demonstrated a high molecular weight material potentially a precursor and a low molecular weight form similar to, but not identical with, porcine motilin (27). Sites and mechanisms of action In the central nervous system and spinal cord, Phillis and Kir kpatrick (28,29) found motilin to be a potent excitatory stimulant of cerebral cortical ~d cortico-spinal neurons. Dieters neurons in the rabbit vestibular nucleus which are inhibited by stimulation of cerebellar nerves were found to be inhibited by application of motilin (30) suggesting that the cerebellar tracts containing motilin-like material (26) are important in the cerebellar influence on vestibular neurons. The motor stimulating action of motilin in the gut has been most closely studied in association with the migrating motor complex (MMC) (see below). In most species tested, except rabbits and humans, isolated strips of gastrointestinal muscle do not respond to motilin in vitro, while the actions of motilin in vivo can be blocked by interference with nerve functions (31,32). These results suggest that motilin acts on nerves to release transmitters, but that the neural sites of action are missing, damaged, or lack input to the nerves remaining in the in vitro situation (6,31,32,33,34). In the rabbit, the motor response of gastrointestinal muscle strips in vitro was not affected by the neural blocking agent tetrodotoxin or antagonists such as hexamethonium, atropine, cimetidine, cinariserin, or aspirin suggesting a direct smooth muscle action. Since the response was eliminated by incubation in calcium-free media or pre-incubation with verapamil, motilin was presumed to act by increasing calcium influx from extracellular sources (34,35,36,37). Intravenous little effect
bolus injections of synthetic or natural porcine motilin have in the fed state, but in the fasted state, motilin injections
Vol. 35, No. 7, 1984
Motilin -- an Update
697
induce premature activity fronts of the MMC of the upper gastrointestinal tract in man and dog (see Wingate 1981, for a comprehensive review) (11). Porcine motilin had no such effect in the pig (38). Since the naturally occurring or motilin-induced complex is blocked by atropine (39) and tetrodotoxin (TTX) (40), motilin presumably acts to release acetylcholine and/or other neurotransmitters. The mechanism by which this occurs has been most closely examined in dogs. In the canine stomach studied ex vivo (33) and in vivo (31), close intraarterial injections of motilin produce prolonged phasic activity which was reduced by hexamethonium and totally blocked by atropine or tetrodotoxin suggesting that motilin acts to release acetylcholine in the stomach. In the small intestine, similar to the stomach, TTX completely abolishes the prolonged phasic contractions produced by intraarterial motilin. However, either hexsmethonlum or atropine alone reduce but do not abolish the response, and the combination of hexamethonium and atropine is required to eliminate the response (32). Thus, in the small intestine, motilin apparently releases acetylcholine and another unknown transmitter which acts via a nicotinic synaptic link to stimulate motility. In this last study, the ileum was found to be considerably less sensitive to intraarterial motilin than the upper small intestine or stomach. This probably explains why in intact animals, motilin is ineffective in initiating premature MMCs in the lower small intestine (41). Among the excitatory peptides, which act at least partially by releasing acetylcholine, only intraarterial injections of the opiates, morphine and met-enkephalin act to produce a prolonged phasic activity similar to motilin (42). Since the phasic response to met-enkephalin was reduced by naloxone, we examined the effect of naloxone on the response to motilin. Naloxone (in doses which did not inhibit responses to intraarterial acetylcholine) similarly increased the concentration required to produce excitation by either motilin or met-enkephalin and atropine had similar effects on responses to both peptides, but abolished responses to acetylcholine. The combination of both antagonists failed to affect the responses to peptides further and did not eliminate the responses to either met-enkephalin or motilin (Fox and Daniel, unpublished data). These results suggest that motilin may release opiate peptides to produce the phasic activity. These opiates may initiate motor activity by releasing acetylcholine or by acting directly on the smooth muscle. If motilin acts by releasing an opiate peptide, it would not be surprising that the opiate agonists such as morphine can, like motilin, initiate premature MMC in the duodenum as demonstrated by Sarna et al. (41) and naloxone can delay the onset of duodenal MMCs (43). Very high concentrations of motilin could still initiate duodenal MMCs in the presence of naloxone in these studies (43) suggesting that motilin was capable of initiating MMCs by activating the naloxone-insensitive opiate receptors described above. In addition to stimulating gastrointestinal motility, motilin intravenously has been reported to induce gall bladder contractions, but only in association with the onset of the MMC (44). This effect in vivo may be in conj~ction with or as a result of the initiation of a premature activity front, since gall bladder contractions are not stimulated by motilin in vitro (45). In summary, in most species motilin acts on nerves in both the CNS and gastrointestinal tract. In the gut, motilin acts to eventually release acetylcholine and unknown transmitters. One candidate for an unknown excitatory transmitter is met-enkephalin.
698
Motilin -- an Update
Vol. 35, No. 7, 1984
Mechanisms of release of immunoreactive motilin Intr alumin al contents. The gastric motor stimulating effects of intraduodenal alkalinization in the presence and absence of atropine in dogs was the initial impetus in the search for motilin (46) and, therefore, once radioimmunoassays (RIAs) for motilin were developed, the capacity of duodenal alkalinization to release motilin into peripheral plasma of the dog was demonstrated (47,48). However, in man, duodenal alkalinization with Tris did not increase plasma I-motilin levels nor did it produce the gastric motor activity. Duodenal acidification, however, was found to increase plasma motilin levels in man (49,50). When motility and peripheral venous I-motilin were measured concomitantly in both man and dog using the same antibody for RIA (51,52), the true species differences were found. Increased peripheral plasma motilin levels, and both gastric and duodenal motility increases including induction of migrating motor complexes were initiated by Tris at pH 10.2 in the canine duodenum, while in man intraduodenal Tris infusion neither altered motility nor increased I-motilin peripherally. Duodenal acidification induced a short-lived increase in duodenal activity in the dog with little change in peripheral motilin, while in man duodenal activity induced by acidification resembled the MMC and peripheral plasma motilin levels showed a delayed rise (51,53). In neither species did duodenal acidification increase gastric motility. The pig appears to resemble man in that duodenal acidification raises I-motilin levels (54). Following a mixed meal, motilin levels rise very little both in man and dog (49,51,52,55). This is presumably due to the proportion of fat, protein, and carbohydrates since carbohydrate meals depress motilin levels, and fats and proteins raise them (55). In particular, oral fat ingestion is a potent stimulus of increases in peripheral plasma I-motilin levels in man and dog (51,52). Fat ingestion is the natural stimulant of gall bladder emptying. In the dog, the activity of the bile may be sufficient to increase plasma motilin by raising intraduodenal pH, but in man increases in pH induced by Tris do not alter plasma I-motilin levels. However, exposure of the duodenum to bile may alter not only the local pH, but may have other actions not reproduced by Tris. Therefore, it is of interest that exposure of human duodenal mucosa in vitro to 15 Na taurocholate did release significant amounts of I-motilin (55). Furthermore, Domschke et al. (56) reported that exogenous and endogenous bile in the duodenum increased peripheral I-motilin levels. As well, when gall bladder emptying in man was evaluated by radioactive scanning, peaks in peripheral I-motilin were found only after the gall bladder had emptied its contents into the duodenum (57). Thus, in man a potent physiological stimulus for motilin-release may be release of bile into the duodenum. Neural activity and ~astrointestinal
motility
The association of peaks in peripheral plasma motilin with passage of the migrating motor complex through the upper gastrointestinal tract in dogs, man, and opossums is well established although some discrepancies still remain (see below) (58,59,60, 61). Vagal and other cholinergic neural input have been implicated in control of these complexes (62,63) since efferent vagal traffic was associated with gastric activity fronts and chilling the vagus eliminated the gastric activity front. Vagal stimulation has been shown to increase I-motilin concentrations in peripheral plasma in anaesthetized dogs (64), but only after prolonged stimulation at high frequency with long duration pulses (64,65). However, we (64) also showed that when plasma samples were collected from local duodenal veins during stimulation of the vagus at parameters within the usual values (5 ms, 5 Hz) significant I-motilin release occurred, as well as
Vol. 35, No. 7, 1984
Motilin -- an Update
699
increases in duodenal motility. Increases in antral, but not duodenal motility, following stimulation of the nerve of Latarjet or intraarterial carbachol to the antrum and excitation of duodenal contractions by field stimulation of duodenal intrinsic nerves, all increased local I-motilin release. Since all these events were blocked by hexamethonium or by atropine, the neural input to motilin containing cells appeared to utilize a pathway containing both a nicotinic and a muscarinic receptor. The fact that the muscarinic receptor involved in motilin-release could be activated by intraarterial carbachol in the presence of tetrodotoxin suggested that the muscarinic receptor is on the motilin-containing cell. Since there was a significant relationship between duodenal motor activity and amount of local I-motilin release and suppression of spontaneous motor activity by atropine reduced resting I-motilin levels, we concluded that motor activity itself may release motilin. Motilin itself was also shown to release motilin even in the presence reduced motor activity after atropine; i.e. infusions of porcine motilin were shown to increase peripheral levels of canine motilin measured using a double antibody technique (66). This provides the basis for a positive feedback loop leading to massive motilin-release. In summary, intraluminal evmts such as release of biliary contents, increased neural activity of gastrointestinal cholinergic nerves, motilin-release, and gastrointestinal motor activity all release I-motilin. What is the relationshi p between motilin and the misratin$ motor complex? Analysis of fluctuation in peripheral plasma I-motilin concentrations as they relate to the events in the migrating motor complex have revealed the following patterns. In the dog, the peaks are associated with passage of the f~ont through the duodenum ( 6 7 ) . This is true whether the duodenal complex occurs during fasting or feeding (68,69) and is independent of vagal activity and a gastric MMC phase, i.e. as demonstrated during the chilling of the vagus by Hall et al. (70). Activity fronts which start in the jejunum similar to those initiated by somatostatin (67,71) are not associated with peaks in plasma motilin (72). Our studies on release of motilin into duodenal veins (64), as well as those of the Rochester, New York group (65) show that although duodenal portal plasma vein show significant increases in I-motilin, only prolonged vagal stimulation at high frequencies was capable of producing significant increases in peripheral plasma levels. These rises were delayed as compared to both local release and motor activity. Such findings probably reflect distribution, dilution, and degradation of the peptide in the general circulation. Thus for significant increases in peripheral plasma levels to be demonstrated, the events which occur in the duodenum during passage of the activity phase must release a major quantity of I-motilin. In man, the difficulty in correlating peaks of I-motilin with motility events, i.e. peaks of peripheral I-motilin occurred without duodenal complexes and duodenal complexes without peaks (60) was approached by carrying out statistical analysis and peaks of I-motilin were found to co-vary with appearance of the activity in the upper duodenum (72). However, further analysis of their data has led the Leuven group to the conclusion that only those complexes which start in the stomach are regularly associated with peaks peripheral plasma in I-motilin which according to their data just preceed the gastric Phase III (73). In the opossum, the I-motilin peak coincided with the Phase III activity in the duodenum and sphincter of Oddie (61).
700
Motilin -- an Update
Vol. 35, No. 7, 1984
What events could account for measurable rises in peripheral plasma I-motilin levels associated with the mi~ratin~ motor complexes? In the dog, the motor activity of the duodenum itself might account for measurable I-motilin release (64). Stimulation of the motilin containing structure probably occurs via an intrinsic cholinergic neural pathway (see above). This then could account for the I-motilin peaks seen during vagal-independent duodenal complexes (70) which can be induced both during fasting and feeding by eliminating vagal activity. Other neural events contributing to the peaks would include increased vagal activity (62,64) and gastric motor activity (64). Release of motilin was shown to be sensitive in the dog to changes in pH (47). Futher factors ~hich could account for the I-motilin peaks could be the emptying of bile and pancreatic secretions into the duodenum (74) and their propulsion through the upper small intestine (75) which occurs just prior to the onset of Phase III and with the first wave of contraction respectively (76). This has yet to be tested in the dog. In man, there is no direct information available about the role of motor activity of the gut itself in releasing motilin although the statistical studies of Peeters et al. (70) should be interpreted as an association. However, the most recent studies from that group (71) suggest that the peak I-motilin values preceed the gastric activity front. Furthermore, the motor component in the duodenum is preceeded (8 minutes) by pancreatic and biliary emptying into the duodenum (75) and Svenberg et al. (57) found peaks motilin followed gall bladder emptying (i.e. appearance of radiolabelled bile in the duodenum) during fasting. These events may well be linked, but the study of gall bladder emptying and I-motilin release (57) did not measure motility, that of the gastric activity fronts and I-motilin (73) did not measure gall bladder emptying, and the study of motility and the duodenal alkalinization did not measure I-motilin (77). If one takes into account the previous findings that a very potent stimulus for I-motilin release is fat ingestion (49,50,51) which would stimulate gall bladder contractions and Na Taurocholate can release I-motilin in vitro (55), one can hypothesize that the events which initiate the gastric activity phase (in all likelihood efferent activity in the vagus) also initiate gall bladder contraction. Thus, the duodenum would be filled with bile salts and as the wave of the contraction moves this material along, the upper gut is sequentially exposed to the bile and motilin would be released from the endocrine cells found in high density in the upper gut (78). To test such a hypothesis, a careful evaluation is necessary of the exact sequence of events; that is, vagal activity, gastric and duodenal motor activity, I-motil in rise, and the appearance of bile in the small intestine. Also, interventions to break links (e.g., diversion of bile) in the chain of events, need to be studied. Is motilin necessary for the presence of these activity fronts? Although motilin intravenously will initiate premature activity fronts in both man and dog (see Wingate, 11 for review), in the pig neither motilin infusions (38) nor immunoneutralization of motilin (79) alter the rate of activity front initiation and, therefore, motilin would appear not to be necessary for the passage of the front in the pig. In man, there is a clear association of motilin peaks only with gastric activity fronts, and possibly gall bladder emptying. The necessity of the presence of motilin for these fronts has been questioned previously (60). Only in the dog is there evidence for any necessity for increased motilin-release during the passage of the activity front through the upper gut. The lower gut activity fronts have been shown to be totally motilin-independent whether the gut is intact (67) or has been surgically isolated and denervated (80,81). Chey and colleagues have shown
Vol. 35, No. 7, 1984
Motilin -- an Update
701
that the activity fronts of the antrum and duodenum could be greatly delayed by the administration of motilin-specifie antiserum (82), while the fronts continued to occur in the ileum. The jejunual fronts returned before either duodenal and antral fronts. Furthermore, in other studies, when the gall bladder emptying of bile was diverted, there was a delay in the onset of the following upper gut activity front in the dog (76). This was also true for the opossum (83) and the baboon (84). The motilin released by this bile passage could be necessary for consolidation of the next front although many other factors may be involved. Thus, there is evidence for plasma motilin playing a physiological role in the generation activity fronts in the duodenum in dogs. Less clear evidence is available in man, but in pigs, motilin in plasma plays no essential role. How could motilin act in the activity front ~eneration? In the dog, motilin acts to increase motor activity by stimulating release of acetylcholine in the stomach and acetylcholine, endogenous opiates, and other neurotransmitters in the small intestine (31,32). Increases in vagal activity, emptying of bile into the duodenum, and an increase of motor activity have all been shown to both be initial events of the upper gastrointestinal activity front, as well as being factors which will release I-motilin. Taken together, these events could release sufficient motilin to further increase motility such that the activity becomes consolidated into an activity front. Thus, each of these events by itself may not be able to initiate the activity front, but all may be required to consolidate the irregular but heightened activity of Phase II into a proper activity front. The elements of a positive feedback loop (motilin-release enhanced by the motor activity induced by vagal activity may further enhance motilin-release) exist in the system. The ability of motilin to induce premature activity fronts when given at 40% of the small intestinal cycle (85) (i.e., during the relative refractory period) may reflect its ability to precipitate activity within this positive feedback loop. In the case of the stomach which lacks motilin, motilin could not be released locally, but could reach the stomach via the circulation, i.e. it would probably act as an endocrine agent (20). For motilin to induce a gastric complex, vagal activity must be present (63) as even with peaks of I-motilin associated with duodenal complexes, chilling of the vagus leads to complete cessation of gastric activity. In the duodenum, the motilin may reach the intrinsic and extrinsic excitatory nerves via both an endocrine route or via a paracrine route, as motilin released from local structures may reach and stimulate nerves by diffusing from endocrine or neural sources (23). For motilin both to be released and to stimulate motility to consolidate the motor activity front, the cholinergic innervation must be intact since atropine and hexamethonium each both reduce the response to motilin (30,31), block release of motilin (64) and inhibit the initiation of duodenal activity fronts (39); all of which actions may contribute their ability to inhibit the complex (39). Further evidence that the local intrinsic nerves must be intact is obtained from the local denervation with tetrodotoxin, which inhibits the local propagation of the complex (40). Thus motilin, at least in the dog, man, and the opossum, probably does not initiate the upper gastrointestinal tract activity fronts, but its release by the events, both intrinsic and extrinsic, which do initiate the event, may facilitate consolidation of the hightened activity into the propogating wave of contractions.
702
Motilin -- an Update
Vol. 35, No. 7, 1984
Motilin and pathological conditions Although peripheral plasma has been assayed for I-motilin in association with a variety of pathological conditions, rarely has the concomitant motility and especially the motor patterns in the fasting state been monitored. Furthermore, post-prandial I-motilin secretion patterns vary with the composition of the meal and could vary with alterations in gastric emptying or enzyme secretions associated with the pathological states as with anticipation of a meal (86). Thus, it is difficult to interpret such studies in light of true alterations in I-motilin levels and whether motilin if elevated is a result of the pathology or produces pathological changes. Elevations in pre- and post-prandial I-motilin concentrations have been reported by Bloom and his colleagues for acute infective diarrhea (87), inflammatory bowel disease (88), tropical malabsorption (89), and bowel resection (90). In addition, consistently elevated plasma I-motilin levels were found for a week following abdominal surgery with or without surgical manipulation of the small bowel by Fujimoto et al. (91). Once normal bowel habits were restored, I-motilin levels fell to pre-surgical levels in these patients. In patients with renal failure I-motilin levels were found to be greatly elevated (92). These elevations were not reduced by dialysis, but returned to control values following renal transplant in 5 patients. From these ~ndings an important role for the kidney in motilin degredation in man was suggested. In patients with systemic sclerosis who have measurable MMCs, there was cycling of plasma I-motilin, but no information was given concerning I-motilin concentrations over time in patients which did not have MMCs (93). Patients with gall stone disease with MMCs also showed cyclic patterns of I-motilin (94). Thus, at present, there is no clear cut association of altered motilin concentrations with pathological conditions except renal disease and the elev~ i o n can be explained by loss of the degredation mechanism. In the case of diarrheal disease studies, the motilin elevations could well have been a result of the altered motility (not measured) or the elevations of motilin could possibly have aided in producing the altered motility in diarrhea. For any understanding of the role of motilin in pathological conditions, detailed studies of the migrating motor complex, its secretory and motor components in the pathological condition must be made in association with I-motilin measurements. Furthermore, only with the development of a selective motilin antagonist will it be possible to determine the contribution made by increased motilin concentrations to any pathological state. Areas for further study The knowledge of the sequences of motilin in various species and the availability of these species-specific motilin molecules will allow more careful evaluation of its sites of origin, and sites and mechanisms of action in both neural and non-neural target cell. Studies of motilin molecular heterogeneity should also permit analysis of the various motilln molecules present within any given species to determine the role motilin heterogeneity plays in physiological and pathological control functions of motilin. Studies on the mechanism of the release of motilin must take into account the associated motor activity of the gastrointestinal tract and the lumen contents of the gut. Studies on the relationship of motilin to the migrating motor complex require attention to the above details, as well as the relationship of motilin levels to other circulating peptides. With the development of a selective motilin antagonist, the role of motilin in the MMC and a variety of physiological and pathological conditions can be determined.
Vol. 35, No. 7, 1984
Motilin -- an Update
703
Ac kn0wled~ement s Dr. J.E.T. Fox is a Scholar of the Canadian Medical Research Council. Much thanks to Dr. E.E. Daniel, Dr. N. Diamant, and K.H. Hull for their helpful suggestions, and Helen Wagner for secretarial assistance. References I. 2. 3.
4. 5. 6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
23. 24. 25.
J.C. BROWN, V. MUTT and J.R. DRYBURGH, Can. J. Physiol. Pharmacol. 49 399-405 (1971). J.C. BROWN, M.A. COOK and J.R. DRYBURGH, Can. J. Biochem. 51 533-537 (1973). E. WUNSCH, J.C. BROWN, K.H. DIEMER, F. DREES, E. JAEGER, J. MUSIOL, R. SCHARF, H. STOCKER, P. THAMM and G. WENDLBERGER, Naturtauschung 28 235-240 (1973). H. SCHUBERT and J.C. BROWN, Can. J. Biochem. 52 7-8 (1974). P. POITRAS, J.R. REEVE, Jr., M.W. HUNKAPILLER, L.E. HOOD and J.H. WALSH, Regulatory Peptides 5 197-208 (I 983). W. DOMSCHKE, Am. J. Dig. Dis. 22 (1977). J.C. BROWN and J.R. DRYBUR(~, in Gut Hormones (Ist edition), edited by S.R. Bloom, pp. 327-331 Churchill Livingstone, Edinburgh (1978). H.S. McINTOSH and J.C. BROWN, in Gastrointestinal Hormones, edited by G.B. Jerzy Glass, pp. 233-244, Raven Press, New York (1980). N.D. CHRISTOFIDES and S.R. BLOOM, in Gut Hormones (2nd edition), edited by S.R. Bloom and J.M. Polak, pp. 271-279, Churchill Livingstone, Edinburgh (1981). Z. ITOH, in Gut Hormones, edited by S.R. Bloom and J.M. Polak, pp. 280-289, Churchill Livingstone, Edinburgh (1981). P.L. WINGATE, Dig. Dis. Sci. 26 641-666 (1981). L. DEMLING and W. DOMSCHKE, Scand. J. Gastroent. 11 1-118 (1976). A.G.E. PEARSE, Stand. J. Gastroent. 11 35-38 (1976). P.U. HEITZ, M. KASPER, G. KREY, J.M. POLAK and A.G.E. PEARSE, Gastroenterology 74 71 3-717 (I 978). W.G. FORSSMANN, N. YANAIHARA, V. HELMSTAEDTER and D. GRUBE, Scand. J. Gastroent. 11 43-45 (I 976). V. ~LMSTAEDTER, W. KREPPEIN, W. DOMSCHKE, P. MITZNEGG, N. YANAIHARA, E. WUNSCH and W.G. FORSSMANN, Gastroenterology 76 897-902 (1979). J.M. POLAK and A.M. BUCHAN, Gastroenterology 76 1065-1066 (1979). J. DAWSON, M.G. BRYANT, A.G. COX, N.D. CHRISTOFIDES, S.R. BLOOM and T.J. PETERS, Clin. Sci. 59 505-508 (1980). S. SHIN, K. IMAGAWA, F. SHIMIZU, E. HASHIMURA, K. NAGAI, C. YANAIHARA and N. YANAIHARA, Endocrinol. Japon. S.R. 141-149 (1980). N.D. CHRISTOFIDES, M.G. BRYANT, M.A. GHATEI, S. KISHIMOTO, A.M. BUCHAN, J.M. POLAK and S.R. BLOOM, Gastroenterology 80 292-300 (1981). N. YANAIHARA, C. YANAIHARA, K. NAGAI, H. SATO, F. SHIMIZU, K. YAMAGUCHI and K. ABE, Biomed. Res. 1 76-83 (1980). C. YANAIHARA, H. S~TO, N. YANAIHARA, S. NARUSE, W.G. FORSSMANN, V. HELMSTAEDTER, T. FUJITA, K. YAMAGUCHI and K. ABE, Adv. Exp. Med. Biol. 106 269-283 (1978). J.E.T. FOX, N.S. TRACK, E.E. DANIEL and N. YANAIHARA, Biomed. Res. 2 (1981). V. CHAN-PALAY, G. NILAVER, S.L. PALAY, M.C. BEINFELD, E.A. ZIMMERMAN, J.Y. WU and T.L. O'DONOHU, Proc. Natl. Aead. Sci. 78 7787-7791 (1981). D.M. JACOBOWITZ, T.L. O'DONOHUE, W.Y. CHEY and T.M. CHANG, Peptides 2 479-487 (1981).
704
26. 27.
28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49.
50. 51. 52. 53. 54. 55.
Motilin -- an Update
Vol. 35, No. 7, 1984
G. NILAVER, R. DEFENDINI, E.A. ZIMMERMAN, M.C. BEINFELD and T.L. OVDONOHUE, Nature 295 597-598 (I 982). T.L. O'DONOHUE, M.C. BEINFELD, W.Y. CHEY, T.M. CHANG, G. NILAVER, E.A. ZIMMERMAN, H. YAJIMA, H. ADACHI, M. POTH, R.P. McDEVITT and D.M. JACOBOWITZ, Peptides 2 467-477 (1981). J.W. PHILLIS and J.R. KIRKPATRICK, European J. Pharmacol. 58 469-472 (1979). J.W. PHILLIS and J.R. KIRKPATRICK, Can. J. Physiol. Pharmacol. 58 612-623 (1980). V. CHAN-PALAY, M. ITO, P. TONGROACH, M. SAKURAI and S. PALAY, Pro. Natl. Aead. Sci. 79 3355-3359 (1982). J.E.T. FOX, E.E. DANIEL, J. JURY, A.E. FOX and S.M. COLLINS, Life Sci. 33 817-825 (1983). J.E.T. FOX, E.E. DANIEL, J. JURY and H. ROBOTHAM, Life Sci. (1984) (in print). M.A. COOK, K. KOWALEWSKI and E.E. DANIEL, Mater Med. Pol. (Engl. Ed.) 9 113-117 (1977). T. SEGAWA, N. NAKANO, Y. KAI, H. KAWATANI and H. YAJIMA, J. Pharmacol. 28 650 (1976). T. SEGAWA, M. NAKAMO, Y, KAI, H. KAWATANI and H. YAJIMA, J. Pharmacol. 28 650-651 (1976). H. ADACHI, N. TODA, S. HAYASHI, M. NOGUCHI, T. SUZUKI, K. TORIZUKA, H. YAJIMA and K. KOYAMA, Gastroenterology 80 783-788 (1981). J. RIEMER, K. KOLLING and C.J. MAYER, Pflugers Arch. 372 243-250 (1977). L. BUENO, J. FIORAMONTI, V. RAYNER and Y. RUCKEBUSCH, Gastroenterology 82 1395-1402 (1982). H.S. ORMSBEE III, G.L. TELFORD and G.R. MASON, Am. J. Physiol. 237 E451-E456 (I 979). S. SARNA, C. STODDARD, L. BELBECK and D. McWA~E, Am. J. Physiol. 241 616-(]23 (1981). S. SARNA, R.E. CONDON and V. COWLES, Am. J. Physiol. 245 G217-G220 (1983). E.E. DANIEL, T. GONDA, T. DOMOTO, M. OKI and N. YANAIHARA, Can. J. Physiol. Pharmaeol. 60 830-840 (1982). G.L. TELFORD and J.H. SZURSZEWSKI, Gastroenterologie Clin, Biol. 7 717-718 (1983). I. TAKAHASHI, T. SUZUKI, I. AIZAWA and Z. ITOH, Gastroenterology 82 419-424 (1982). I.S. POMERANZ, J.S. DAVISON and E.A. SHAFFER, Dig. Dis. Sci. 28 539-544 (1983). J.C. BROWN, L.P. JOHNSON and D.F. MAGEE, Gastroenterology 50 333-339 (I 965). J.R. DRYBURGH and J.C. BROWN, Gastroenterology 68 1169-1176 (1975). K.Y. LEE, W.Y. CHEY, H.H. TAI and H. YAJIMA, Dig. Dis. 23 789-795 (1978). P. MITZNEGG, S.R. BLOOM, N. CHRISTOFIDES, H. BESTERMAN, W. DOMSCHKE, S. DOMSCHKE, E. WUNSCH and L. DEMLING, Scand. J. Gastroenterol. 11 (Suppl. 39) 53-56 (1976). P. MITZNEGG, S.R. BLOOM, W. DOMSCHKE, S. DOMSCHKE, E. WUNSCH and L. DEMLING, Lancet I 888-889 (1976). S.M. COLLINS, ~.D. LEWIS, J.E.T. FOX, N.S. TRACK, M.M. MEGHJI and E.E. DANIEL, Can. J. Physiol. Pharmacol. 59 188-194 (1981). J.E.T. FOX, N.S. TRACK and E.E. DANIEL, Can. J. Physiol. Pharmacol. 59 180-181 (1981). T.D. LEWIS, S.M. COLLINS, J.E.T. FOX and E.E. DANIEL, Gastroenterology 77 1217-1224 (1979). I.M. MODLIN, P. M I T Z ~ G G and S.R. BLOOM, Gut 19 399-402 (1978). S. SAITO, T. OGAWA, H. SAITO, K. ISHIMARU, I. OSHIMA and Y. SONAKA, Endocrinol. Japou. S.R. 157-162 (1980).
Vol. 35, No. 7, 1984
56. 57. 58. 59. 60. 61.
62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86.
Motilln -- an Update
705
W. DOMSCHKE, G. LUX, P. MITZEGG, S. NEEB, U. STROWZ and S. DOMSCHKE, Gastroenterology 76 1123 (1979). F. AREOLA-ORTIZ, S.R. T. SVENBERG, N.D. CHRISTOFIDES, M.L. FITZPATRICK, BLOOM and R.B. WELBOURN, Gut 23 1024-1028 (1982). Z. ITOH, S. TAKEUCHI, I. AIZAWA, K. MORI, T. TAMINATO, Y. SEINO, H. IMURA and N. YANAIHARA, Dig. Dis. 23 929-935 (1978). G. VANTRA?PEN, J. JANSSENS, T.L. PEETERS, S.R. BLOOM, N.D. CHRISTOFIDES and J. HELLEMANS, Dig. Dis. Soi. 24 497-500 (1979). E.E. DANIEL, J,E.T. FOX, S . M . COLLINS, T.D. LEWIS, M. MEGHJI and N.S. TRACK, Can. J. Physiol. Pharmacol. 59 173-179 (1981). I. TAKAHASHI, R. HONDA, W.J. DODDS, S. SARNA, J. TOOULI, Z. ITOH, W.Y. C~Y, W.J. HOGAN, D. GREIFF and K. BAKER, Am. J. Physiol. _8 G476-G491 (I 983). J.P. MIOLAN and C. ROMAN, Am. J. Physiol. 235 E366-E373 (1978). K.E. HALL, T.Y. EL-SHARKAWY and N.E. DIAMANT, Am. J. Physiol. G276-G284 ( 1982 ). J.E.T. FOX, E.E. DANIEL, J. JURY, N.S. TRACK and S. CHIU, Can. J. Physiol. Pharmacol. 61 1042-1049 (1983). K.Y. LEE, T. CHANG and W.Y. CHEY, Life Sei. 29 1093-1097 (1981). K.E. HALL, G.R. GREENBERG, T.Y. EL-SHAR KAWY and N.E. DIAMANT, Gastroenterology (in press). P. POITRAS, J.H. STEINBACH, G. VanDEVENTER, C.F. CODE and J.H. WALSH, Am. J. Physiol. 239 G215-G220 (1980). S. SARNA, W. CHEY, R. CONDON, W. IX)DIE, T. MEYERS and T. CHANG, Gastroenterologie Clin. Biol. 7 717 (I 983). S. SARNA and R.E. CONDON, Gastroenterologie Clin. Biol. _7 721 (1983). K.E. HALL, G.R. GREENBERG, T.Y. EL-SHARKAWY and W.E. DIAMANT, Can. J. Physiol. Pharcol. 61 1289-1298. P. THOR, K. KROL, S.J. KONTUROK, D.H. COY and A. V. SCHORLY, Am. J. Physiol. 235 E249-E254 (1978). T.L. PEETERS, G. VANTRAPPEN and J. JANBSENS, Gastroenterology 79 716-719 (1980). J. JANSSENS, G. VANTRAPPEN and T.L. PEETERS, Regulatory Peptides 6 363-369 (1983). F . B . KEANE, E.P. DiMAGNO, R.R. DOZOIS and V.L. GO, Gastroenterology 78 310-316 (1980). R . B . SCOTT, S.M. STRASBERG, T.Y. EL-SHARKAWY and N.E. DIAMANT, J. Clin. Invest. 71 644-654 (1983). R.B. SC'-OTT, S.M. STRASB ERG, T.Y. EL-SHARKAWY and N . E . DIAMANT, Gastroenterology (in press). G. LUX, J. FEMPPEL, P. LEDERER, W. ROSCH and W. DOMSCHKE, Acta Hepato-Gastroenterol. 26 166-169 (I 979). K. SJOLUND, G. SANDI'-N, R. HAKANBON and F. SUNDLER, Gastroenterology 85 1120-1130 (1983). T. BORODY, D. BYRNES, J. SLOWIACZEK and D. TITCHEN, Horm. Metab. Res. 35 417-420 (1981). J. PINNINGTON and D.L. WINGATE, J. Physiol. (London) 337 471-478 (1983). M.G. SAIR, K.A. KELLY and V.L. GO, Dig. Dis. Soi. 28 249-256. K.Y. LEE, T.M. CHANG and W.L. CHEY, Am. J. Physiol. 245 G547-G553 (1983). I. TAKAHASHI, W.J. DODDS, H. AMMON, W.J. HOGAN and K. MATHENY, Gastroenterology 84 1329 (1984). R . W . REDINGER, A.M. MORELLO and W.W. LA MORTE, Gastroenterology 80 1259 (1981). S. SARNA, W.Y. CHEY, R.E. CONDON, W.J. DODIE, T. MYERS and T.A. CHANG, Am. J. Physiol. 245 G277-G284 (1983). J.H. STEINBACK and C.F. CODE, in Gastrointestinal Motility, edited by J. Christensen, pp. 247-252, Raven Press, New York (1980).
706
87. 88. 89. 90.
91. 92. 93. 94.
Motilin -- an Update
Vol. 35, No. 7, 1984
H.S. BESTERMAN, N.D. CHRISTOFIDES, P.D. WELSBY, T.E. ADRIAN, D.L. SARSON and S.R. BLOOM, Gut 24 665-671 (1983). H.S. BESTERMAN, S.R. BLOOM, N.D. CHRISTOFIDES, C.N. MALLINSON, A. PERA and R. MODIGLIANI, Gut 19 988-989 (1978). H.S. BESTERMAN, G.C. COOK and D.L. SARSON, Br. Med. J. 2 1252-1255 (1979). H.S. BESTERMA N, T.E. ADRIAN, C.N. MALLINSO N, N.D. CHR ISTOFIDES, D.L. SARSON, A. PERA, L. LOMBARDO, R. MODIGLIANI and S.R. BLOOM, Gut 23 854-861 (1982). S. FUJIMOTO, M. MIYAZAKI, H. ISHIGAMI, Y. TSORUTA and K. OKUI, Acta Chit. Stand. 148 33-37 (1982). K. SHIMA~ A. TANAKA, N. SAWAZAKI, J. HAMABE, R. TANAKA, Y. KOMAHARA and N. YANAIHARA, Horm. Metab. Res. 11 320-321 (1979). W.D. REES, R.J. [SIGH, W.D. CHRISTOFIDES, S.R. BLOOM and L.A. TURNBERG, Gastroenterology 83 575-580 (I 982). R. KLAPDON and E. HAMMER, Klin. Woehenschr. 61 251-253 (1983).
Pergamon Press
MINIREVIEW MOTILI N--AN UPDATE J.E.T. Fox School of Nursing and Department of Neurosciences, McMaster University Hamilton, Ontario, Canada LSN 3Z5
Summ sr y 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 immtmoreactive 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. The search by J.C. Brown for duodenal factors which stimulate canine gastric motility following duodenal alkalinization culminated in the isolation, sequencing, and synthesis of the 22 amino acid peptide porcine motilin (1,2,3,4). It is this peptide (both synthetic and natural) which has been used to study the action of motilin and to develop antibodies for radioimmunoassay (RIA) and immunohistochemical (IHC) studies. This may have led to much of the controversy relating to the origin, action, and release of motilin since relevant studies have rarely been made in the pig. The only other motilin which has been isolated, but not yet synthesized, canine motilin, differs in at least 5 of the 22 amino acids (5) and may be regulated and function differently. The present review will deal with recent findings on the localization of motilin, its sites and mechanisms of action, the mechanisms of its release, the relationship of motilin to the migrating motor complex (MMC), and to pathological conditions. The reader is directed to the reviews by Domsehke (6), 0024-3205/84 $3.00 + .00 Copyright (c) 1984 Pergamon Press Ltd.
696
Motilin -- an Update
Vol. 35, No. 7, 1984
Brown and Dryburg (7), McIntosh and Brown (8), Christofides and Bloom (9), Itch (I0), and Wingate (11), as well as the Proceedings of the Erlangen Symposium on Motilin (12) for an analysis of earlier studies. Localization The controversy concerning whether the gut endocrine cell containing motilin is mainly an enterochromaffin (EC) cell containing serotonin (13,14) or a different non-serotonin containing cell (15,16) r e m ~ n s unsettled. The different findings have been attributed to different antisera (17), to different stages of maturation of the EC cell and hence, differing serotonin content (18) and to heterogeneity of the motilin molecule (19,20,21). Yanaihara et al. (22) ~ r s t suggested that motilin or a motilin-like material might also have a neural origin since extracts of central nervous system revealed a high level of immunoreactive (I) motilin. Extracts of canine and opossum gut muscle layers separated from the mucosa also revealed high I-motilin levels. The highest content in either species was found in the jejunum as compared to the ileum, duodenum, or stomach. These results suggest a neural origin in the gut with a similar overall distribution as endocrine cell I-motilin (23), as well as in the CNS. To date, the only reported localization in nerves by imm~mohistochemistry is in the CNS of the rat. Motilin-like material appeared to be localized in fore brain structures and Purkinje cells of the cerebellum (24,25,26). However, in these studies, most motilin antibodies failed to recognize the motilin-like material in Purkinje cells. Initial biochemical analysis of the motilin-like material f~om whole rat brain demonstrated a high molecular weight material potentially a precursor and a low molecular weight form similar to, but not identical with, porcine motilin (27). Sites and mechanisms of action In the central nervous system and spinal cord, Phillis and Kir kpatrick (28,29) found motilin to be a potent excitatory stimulant of cerebral cortical ~d cortico-spinal neurons. Dieters neurons in the rabbit vestibular nucleus which are inhibited by stimulation of cerebellar nerves were found to be inhibited by application of motilin (30) suggesting that the cerebellar tracts containing motilin-like material (26) are important in the cerebellar influence on vestibular neurons. The motor stimulating action of motilin in the gut has been most closely studied in association with the migrating motor complex (MMC) (see below). In most species tested, except rabbits and humans, isolated strips of gastrointestinal muscle do not respond to motilin in vitro, while the actions of motilin in vivo can be blocked by interference with nerve functions (31,32). These results suggest that motilin acts on nerves to release transmitters, but that the neural sites of action are missing, damaged, or lack input to the nerves remaining in the in vitro situation (6,31,32,33,34). In the rabbit, the motor response of gastrointestinal muscle strips in vitro was not affected by the neural blocking agent tetrodotoxin or antagonists such as hexamethonium, atropine, cimetidine, cinariserin, or aspirin suggesting a direct smooth muscle action. Since the response was eliminated by incubation in calcium-free media or pre-incubation with verapamil, motilin was presumed to act by increasing calcium influx from extracellular sources (34,35,36,37). Intravenous little effect
bolus injections of synthetic or natural porcine motilin have in the fed state, but in the fasted state, motilin injections
Vol. 35, No. 7, 1984
Motilin -- an Update
697
induce premature activity fronts of the MMC of the upper gastrointestinal tract in man and dog (see Wingate 1981, for a comprehensive review) (11). Porcine motilin had no such effect in the pig (38). Since the naturally occurring or motilin-induced complex is blocked by atropine (39) and tetrodotoxin (TTX) (40), motilin presumably acts to release acetylcholine and/or other neurotransmitters. The mechanism by which this occurs has been most closely examined in dogs. In the canine stomach studied ex vivo (33) and in vivo (31), close intraarterial injections of motilin produce prolonged phasic activity which was reduced by hexamethonium and totally blocked by atropine or tetrodotoxin suggesting that motilin acts to release acetylcholine in the stomach. In the small intestine, similar to the stomach, TTX completely abolishes the prolonged phasic contractions produced by intraarterial motilin. However, either hexsmethonlum or atropine alone reduce but do not abolish the response, and the combination of hexamethonium and atropine is required to eliminate the response (32). Thus, in the small intestine, motilin apparently releases acetylcholine and another unknown transmitter which acts via a nicotinic synaptic link to stimulate motility. In this last study, the ileum was found to be considerably less sensitive to intraarterial motilin than the upper small intestine or stomach. This probably explains why in intact animals, motilin is ineffective in initiating premature MMCs in the lower small intestine (41). Among the excitatory peptides, which act at least partially by releasing acetylcholine, only intraarterial injections of the opiates, morphine and met-enkephalin act to produce a prolonged phasic activity similar to motilin (42). Since the phasic response to met-enkephalin was reduced by naloxone, we examined the effect of naloxone on the response to motilin. Naloxone (in doses which did not inhibit responses to intraarterial acetylcholine) similarly increased the concentration required to produce excitation by either motilin or met-enkephalin and atropine had similar effects on responses to both peptides, but abolished responses to acetylcholine. The combination of both antagonists failed to affect the responses to peptides further and did not eliminate the responses to either met-enkephalin or motilin (Fox and Daniel, unpublished data). These results suggest that motilin may release opiate peptides to produce the phasic activity. These opiates may initiate motor activity by releasing acetylcholine or by acting directly on the smooth muscle. If motilin acts by releasing an opiate peptide, it would not be surprising that the opiate agonists such as morphine can, like motilin, initiate premature MMC in the duodenum as demonstrated by Sarna et al. (41) and naloxone can delay the onset of duodenal MMCs (43). Very high concentrations of motilin could still initiate duodenal MMCs in the presence of naloxone in these studies (43) suggesting that motilin was capable of initiating MMCs by activating the naloxone-insensitive opiate receptors described above. In addition to stimulating gastrointestinal motility, motilin intravenously has been reported to induce gall bladder contractions, but only in association with the onset of the MMC (44). This effect in vivo may be in conj~ction with or as a result of the initiation of a premature activity front, since gall bladder contractions are not stimulated by motilin in vitro (45). In summary, in most species motilin acts on nerves in both the CNS and gastrointestinal tract. In the gut, motilin acts to eventually release acetylcholine and unknown transmitters. One candidate for an unknown excitatory transmitter is met-enkephalin.
698
Motilin -- an Update
Vol. 35, No. 7, 1984
Mechanisms of release of immunoreactive motilin Intr alumin al contents. The gastric motor stimulating effects of intraduodenal alkalinization in the presence and absence of atropine in dogs was the initial impetus in the search for motilin (46) and, therefore, once radioimmunoassays (RIAs) for motilin were developed, the capacity of duodenal alkalinization to release motilin into peripheral plasma of the dog was demonstrated (47,48). However, in man, duodenal alkalinization with Tris did not increase plasma I-motilin levels nor did it produce the gastric motor activity. Duodenal acidification, however, was found to increase plasma motilin levels in man (49,50). When motility and peripheral venous I-motilin were measured concomitantly in both man and dog using the same antibody for RIA (51,52), the true species differences were found. Increased peripheral plasma motilin levels, and both gastric and duodenal motility increases including induction of migrating motor complexes were initiated by Tris at pH 10.2 in the canine duodenum, while in man intraduodenal Tris infusion neither altered motility nor increased I-motilin peripherally. Duodenal acidification induced a short-lived increase in duodenal activity in the dog with little change in peripheral motilin, while in man duodenal activity induced by acidification resembled the MMC and peripheral plasma motilin levels showed a delayed rise (51,53). In neither species did duodenal acidification increase gastric motility. The pig appears to resemble man in that duodenal acidification raises I-motilin levels (54). Following a mixed meal, motilin levels rise very little both in man and dog (49,51,52,55). This is presumably due to the proportion of fat, protein, and carbohydrates since carbohydrate meals depress motilin levels, and fats and proteins raise them (55). In particular, oral fat ingestion is a potent stimulus of increases in peripheral plasma I-motilin levels in man and dog (51,52). Fat ingestion is the natural stimulant of gall bladder emptying. In the dog, the activity of the bile may be sufficient to increase plasma motilin by raising intraduodenal pH, but in man increases in pH induced by Tris do not alter plasma I-motilin levels. However, exposure of the duodenum to bile may alter not only the local pH, but may have other actions not reproduced by Tris. Therefore, it is of interest that exposure of human duodenal mucosa in vitro to 15 Na taurocholate did release significant amounts of I-motilin (55). Furthermore, Domschke et al. (56) reported that exogenous and endogenous bile in the duodenum increased peripheral I-motilin levels. As well, when gall bladder emptying in man was evaluated by radioactive scanning, peaks in peripheral I-motilin were found only after the gall bladder had emptied its contents into the duodenum (57). Thus, in man a potent physiological stimulus for motilin-release may be release of bile into the duodenum. Neural activity and ~astrointestinal
motility
The association of peaks in peripheral plasma motilin with passage of the migrating motor complex through the upper gastrointestinal tract in dogs, man, and opossums is well established although some discrepancies still remain (see below) (58,59,60, 61). Vagal and other cholinergic neural input have been implicated in control of these complexes (62,63) since efferent vagal traffic was associated with gastric activity fronts and chilling the vagus eliminated the gastric activity front. Vagal stimulation has been shown to increase I-motilin concentrations in peripheral plasma in anaesthetized dogs (64), but only after prolonged stimulation at high frequency with long duration pulses (64,65). However, we (64) also showed that when plasma samples were collected from local duodenal veins during stimulation of the vagus at parameters within the usual values (5 ms, 5 Hz) significant I-motilin release occurred, as well as
Vol. 35, No. 7, 1984
Motilin -- an Update
699
increases in duodenal motility. Increases in antral, but not duodenal motility, following stimulation of the nerve of Latarjet or intraarterial carbachol to the antrum and excitation of duodenal contractions by field stimulation of duodenal intrinsic nerves, all increased local I-motilin release. Since all these events were blocked by hexamethonium or by atropine, the neural input to motilin containing cells appeared to utilize a pathway containing both a nicotinic and a muscarinic receptor. The fact that the muscarinic receptor involved in motilin-release could be activated by intraarterial carbachol in the presence of tetrodotoxin suggested that the muscarinic receptor is on the motilin-containing cell. Since there was a significant relationship between duodenal motor activity and amount of local I-motilin release and suppression of spontaneous motor activity by atropine reduced resting I-motilin levels, we concluded that motor activity itself may release motilin. Motilin itself was also shown to release motilin even in the presence reduced motor activity after atropine; i.e. infusions of porcine motilin were shown to increase peripheral levels of canine motilin measured using a double antibody technique (66). This provides the basis for a positive feedback loop leading to massive motilin-release. In summary, intraluminal evmts such as release of biliary contents, increased neural activity of gastrointestinal cholinergic nerves, motilin-release, and gastrointestinal motor activity all release I-motilin. What is the relationshi p between motilin and the misratin$ motor complex? Analysis of fluctuation in peripheral plasma I-motilin concentrations as they relate to the events in the migrating motor complex have revealed the following patterns. In the dog, the peaks are associated with passage of the f~ont through the duodenum ( 6 7 ) . This is true whether the duodenal complex occurs during fasting or feeding (68,69) and is independent of vagal activity and a gastric MMC phase, i.e. as demonstrated during the chilling of the vagus by Hall et al. (70). Activity fronts which start in the jejunum similar to those initiated by somatostatin (67,71) are not associated with peaks in plasma motilin (72). Our studies on release of motilin into duodenal veins (64), as well as those of the Rochester, New York group (65) show that although duodenal portal plasma vein show significant increases in I-motilin, only prolonged vagal stimulation at high frequencies was capable of producing significant increases in peripheral plasma levels. These rises were delayed as compared to both local release and motor activity. Such findings probably reflect distribution, dilution, and degradation of the peptide in the general circulation. Thus for significant increases in peripheral plasma levels to be demonstrated, the events which occur in the duodenum during passage of the activity phase must release a major quantity of I-motilin. In man, the difficulty in correlating peaks of I-motilin with motility events, i.e. peaks of peripheral I-motilin occurred without duodenal complexes and duodenal complexes without peaks (60) was approached by carrying out statistical analysis and peaks of I-motilin were found to co-vary with appearance of the activity in the upper duodenum (72). However, further analysis of their data has led the Leuven group to the conclusion that only those complexes which start in the stomach are regularly associated with peaks peripheral plasma in I-motilin which according to their data just preceed the gastric Phase III (73). In the opossum, the I-motilin peak coincided with the Phase III activity in the duodenum and sphincter of Oddie (61).
700
Motilin -- an Update
Vol. 35, No. 7, 1984
What events could account for measurable rises in peripheral plasma I-motilin levels associated with the mi~ratin~ motor complexes? In the dog, the motor activity of the duodenum itself might account for measurable I-motilin release (64). Stimulation of the motilin containing structure probably occurs via an intrinsic cholinergic neural pathway (see above). This then could account for the I-motilin peaks seen during vagal-independent duodenal complexes (70) which can be induced both during fasting and feeding by eliminating vagal activity. Other neural events contributing to the peaks would include increased vagal activity (62,64) and gastric motor activity (64). Release of motilin was shown to be sensitive in the dog to changes in pH (47). Futher factors ~hich could account for the I-motilin peaks could be the emptying of bile and pancreatic secretions into the duodenum (74) and their propulsion through the upper small intestine (75) which occurs just prior to the onset of Phase III and with the first wave of contraction respectively (76). This has yet to be tested in the dog. In man, there is no direct information available about the role of motor activity of the gut itself in releasing motilin although the statistical studies of Peeters et al. (70) should be interpreted as an association. However, the most recent studies from that group (71) suggest that the peak I-motilin values preceed the gastric activity front. Furthermore, the motor component in the duodenum is preceeded (8 minutes) by pancreatic and biliary emptying into the duodenum (75) and Svenberg et al. (57) found peaks motilin followed gall bladder emptying (i.e. appearance of radiolabelled bile in the duodenum) during fasting. These events may well be linked, but the study of gall bladder emptying and I-motilin release (57) did not measure motility, that of the gastric activity fronts and I-motilin (73) did not measure gall bladder emptying, and the study of motility and the duodenal alkalinization did not measure I-motilin (77). If one takes into account the previous findings that a very potent stimulus for I-motilin release is fat ingestion (49,50,51) which would stimulate gall bladder contractions and Na Taurocholate can release I-motilin in vitro (55), one can hypothesize that the events which initiate the gastric activity phase (in all likelihood efferent activity in the vagus) also initiate gall bladder contraction. Thus, the duodenum would be filled with bile salts and as the wave of the contraction moves this material along, the upper gut is sequentially exposed to the bile and motilin would be released from the endocrine cells found in high density in the upper gut (78). To test such a hypothesis, a careful evaluation is necessary of the exact sequence of events; that is, vagal activity, gastric and duodenal motor activity, I-motil in rise, and the appearance of bile in the small intestine. Also, interventions to break links (e.g., diversion of bile) in the chain of events, need to be studied. Is motilin necessary for the presence of these activity fronts? Although motilin intravenously will initiate premature activity fronts in both man and dog (see Wingate, 11 for review), in the pig neither motilin infusions (38) nor immunoneutralization of motilin (79) alter the rate of activity front initiation and, therefore, motilin would appear not to be necessary for the passage of the front in the pig. In man, there is a clear association of motilin peaks only with gastric activity fronts, and possibly gall bladder emptying. The necessity of the presence of motilin for these fronts has been questioned previously (60). Only in the dog is there evidence for any necessity for increased motilin-release during the passage of the activity front through the upper gut. The lower gut activity fronts have been shown to be totally motilin-independent whether the gut is intact (67) or has been surgically isolated and denervated (80,81). Chey and colleagues have shown
Vol. 35, No. 7, 1984
Motilin -- an Update
701
that the activity fronts of the antrum and duodenum could be greatly delayed by the administration of motilin-specifie antiserum (82), while the fronts continued to occur in the ileum. The jejunual fronts returned before either duodenal and antral fronts. Furthermore, in other studies, when the gall bladder emptying of bile was diverted, there was a delay in the onset of the following upper gut activity front in the dog (76). This was also true for the opossum (83) and the baboon (84). The motilin released by this bile passage could be necessary for consolidation of the next front although many other factors may be involved. Thus, there is evidence for plasma motilin playing a physiological role in the generation activity fronts in the duodenum in dogs. Less clear evidence is available in man, but in pigs, motilin in plasma plays no essential role. How could motilin act in the activity front ~eneration? In the dog, motilin acts to increase motor activity by stimulating release of acetylcholine in the stomach and acetylcholine, endogenous opiates, and other neurotransmitters in the small intestine (31,32). Increases in vagal activity, emptying of bile into the duodenum, and an increase of motor activity have all been shown to both be initial events of the upper gastrointestinal activity front, as well as being factors which will release I-motilin. Taken together, these events could release sufficient motilin to further increase motility such that the activity becomes consolidated into an activity front. Thus, each of these events by itself may not be able to initiate the activity front, but all may be required to consolidate the irregular but heightened activity of Phase II into a proper activity front. The elements of a positive feedback loop (motilin-release enhanced by the motor activity induced by vagal activity may further enhance motilin-release) exist in the system. The ability of motilin to induce premature activity fronts when given at 40% of the small intestinal cycle (85) (i.e., during the relative refractory period) may reflect its ability to precipitate activity within this positive feedback loop. In the case of the stomach which lacks motilin, motilin could not be released locally, but could reach the stomach via the circulation, i.e. it would probably act as an endocrine agent (20). For motilin to induce a gastric complex, vagal activity must be present (63) as even with peaks of I-motilin associated with duodenal complexes, chilling of the vagus leads to complete cessation of gastric activity. In the duodenum, the motilin may reach the intrinsic and extrinsic excitatory nerves via both an endocrine route or via a paracrine route, as motilin released from local structures may reach and stimulate nerves by diffusing from endocrine or neural sources (23). For motilin both to be released and to stimulate motility to consolidate the motor activity front, the cholinergic innervation must be intact since atropine and hexamethonium each both reduce the response to motilin (30,31), block release of motilin (64) and inhibit the initiation of duodenal activity fronts (39); all of which actions may contribute their ability to inhibit the complex (39). Further evidence that the local intrinsic nerves must be intact is obtained from the local denervation with tetrodotoxin, which inhibits the local propagation of the complex (40). Thus motilin, at least in the dog, man, and the opossum, probably does not initiate the upper gastrointestinal tract activity fronts, but its release by the events, both intrinsic and extrinsic, which do initiate the event, may facilitate consolidation of the hightened activity into the propogating wave of contractions.
702
Motilin -- an Update
Vol. 35, No. 7, 1984
Motilin and pathological conditions Although peripheral plasma has been assayed for I-motilin in association with a variety of pathological conditions, rarely has the concomitant motility and especially the motor patterns in the fasting state been monitored. Furthermore, post-prandial I-motilin secretion patterns vary with the composition of the meal and could vary with alterations in gastric emptying or enzyme secretions associated with the pathological states as with anticipation of a meal (86). Thus, it is difficult to interpret such studies in light of true alterations in I-motilin levels and whether motilin if elevated is a result of the pathology or produces pathological changes. Elevations in pre- and post-prandial I-motilin concentrations have been reported by Bloom and his colleagues for acute infective diarrhea (87), inflammatory bowel disease (88), tropical malabsorption (89), and bowel resection (90). In addition, consistently elevated plasma I-motilin levels were found for a week following abdominal surgery with or without surgical manipulation of the small bowel by Fujimoto et al. (91). Once normal bowel habits were restored, I-motilin levels fell to pre-surgical levels in these patients. In patients with renal failure I-motilin levels were found to be greatly elevated (92). These elevations were not reduced by dialysis, but returned to control values following renal transplant in 5 patients. From these ~ndings an important role for the kidney in motilin degredation in man was suggested. In patients with systemic sclerosis who have measurable MMCs, there was cycling of plasma I-motilin, but no information was given concerning I-motilin concentrations over time in patients which did not have MMCs (93). Patients with gall stone disease with MMCs also showed cyclic patterns of I-motilin (94). Thus, at present, there is no clear cut association of altered motilin concentrations with pathological conditions except renal disease and the elev~ i o n can be explained by loss of the degredation mechanism. In the case of diarrheal disease studies, the motilin elevations could well have been a result of the altered motility (not measured) or the elevations of motilin could possibly have aided in producing the altered motility in diarrhea. For any understanding of the role of motilin in pathological conditions, detailed studies of the migrating motor complex, its secretory and motor components in the pathological condition must be made in association with I-motilin measurements. Furthermore, only with the development of a selective motilin antagonist will it be possible to determine the contribution made by increased motilin concentrations to any pathological state. Areas for further study The knowledge of the sequences of motilin in various species and the availability of these species-specific motilin molecules will allow more careful evaluation of its sites of origin, and sites and mechanisms of action in both neural and non-neural target cell. Studies of motilin molecular heterogeneity should also permit analysis of the various motilln molecules present within any given species to determine the role motilin heterogeneity plays in physiological and pathological control functions of motilin. Studies on the mechanism of the release of motilin must take into account the associated motor activity of the gastrointestinal tract and the lumen contents of the gut. Studies on the relationship of motilin to the migrating motor complex require attention to the above details, as well as the relationship of motilin levels to other circulating peptides. With the development of a selective motilin antagonist, the role of motilin in the MMC and a variety of physiological and pathological conditions can be determined.
Vol. 35, No. 7, 1984
Motilin -- an Update
703
Ac kn0wled~ement s Dr. J.E.T. Fox is a Scholar of the Canadian Medical Research Council. Much thanks to Dr. E.E. Daniel, Dr. N. Diamant, and K.H. Hull for their helpful suggestions, and Helen Wagner for secretarial assistance. References I. 2. 3.
4. 5. 6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
23. 24. 25.
J.C. BROWN, V. MUTT and J.R. DRYBURGH, Can. J. Physiol. Pharmacol. 49 399-405 (1971). J.C. BROWN, M.A. COOK and J.R. DRYBURGH, Can. J. Biochem. 51 533-537 (1973). E. WUNSCH, J.C. BROWN, K.H. DIEMER, F. DREES, E. JAEGER, J. MUSIOL, R. SCHARF, H. STOCKER, P. THAMM and G. WENDLBERGER, Naturtauschung 28 235-240 (1973). H. SCHUBERT and J.C. BROWN, Can. J. Biochem. 52 7-8 (1974). P. POITRAS, J.R. REEVE, Jr., M.W. HUNKAPILLER, L.E. HOOD and J.H. WALSH, Regulatory Peptides 5 197-208 (I 983). W. DOMSCHKE, Am. J. Dig. Dis. 22 (1977). J.C. BROWN and J.R. DRYBUR(~, in Gut Hormones (Ist edition), edited by S.R. Bloom, pp. 327-331 Churchill Livingstone, Edinburgh (1978). H.S. McINTOSH and J.C. BROWN, in Gastrointestinal Hormones, edited by G.B. Jerzy Glass, pp. 233-244, Raven Press, New York (1980). N.D. CHRISTOFIDES and S.R. BLOOM, in Gut Hormones (2nd edition), edited by S.R. Bloom and J.M. Polak, pp. 271-279, Churchill Livingstone, Edinburgh (1981). Z. ITOH, in Gut Hormones, edited by S.R. Bloom and J.M. Polak, pp. 280-289, Churchill Livingstone, Edinburgh (1981). P.L. WINGATE, Dig. Dis. Sci. 26 641-666 (1981). L. DEMLING and W. DOMSCHKE, Scand. J. Gastroent. 11 1-118 (1976). A.G.E. PEARSE, Stand. J. Gastroent. 11 35-38 (1976). P.U. HEITZ, M. KASPER, G. KREY, J.M. POLAK and A.G.E. PEARSE, Gastroenterology 74 71 3-717 (I 978). W.G. FORSSMANN, N. YANAIHARA, V. HELMSTAEDTER and D. GRUBE, Scand. J. Gastroent. 11 43-45 (I 976). V. ~LMSTAEDTER, W. KREPPEIN, W. DOMSCHKE, P. MITZNEGG, N. YANAIHARA, E. WUNSCH and W.G. FORSSMANN, Gastroenterology 76 897-902 (1979). J.M. POLAK and A.M. BUCHAN, Gastroenterology 76 1065-1066 (1979). J. DAWSON, M.G. BRYANT, A.G. COX, N.D. CHRISTOFIDES, S.R. BLOOM and T.J. PETERS, Clin. Sci. 59 505-508 (1980). S. SHIN, K. IMAGAWA, F. SHIMIZU, E. HASHIMURA, K. NAGAI, C. YANAIHARA and N. YANAIHARA, Endocrinol. Japon. S.R. 141-149 (1980). N.D. CHRISTOFIDES, M.G. BRYANT, M.A. GHATEI, S. KISHIMOTO, A.M. BUCHAN, J.M. POLAK and S.R. BLOOM, Gastroenterology 80 292-300 (1981). N. YANAIHARA, C. YANAIHARA, K. NAGAI, H. SATO, F. SHIMIZU, K. YAMAGUCHI and K. ABE, Biomed. Res. 1 76-83 (1980). C. YANAIHARA, H. S~TO, N. YANAIHARA, S. NARUSE, W.G. FORSSMANN, V. HELMSTAEDTER, T. FUJITA, K. YAMAGUCHI and K. ABE, Adv. Exp. Med. Biol. 106 269-283 (1978). J.E.T. FOX, N.S. TRACK, E.E. DANIEL and N. YANAIHARA, Biomed. Res. 2 (1981). V. CHAN-PALAY, G. NILAVER, S.L. PALAY, M.C. BEINFELD, E.A. ZIMMERMAN, J.Y. WU and T.L. O'DONOHU, Proc. Natl. Aead. Sci. 78 7787-7791 (1981). D.M. JACOBOWITZ, T.L. O'DONOHUE, W.Y. CHEY and T.M. CHANG, Peptides 2 479-487 (1981).
704
26. 27.
28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49.
50. 51. 52. 53. 54. 55.
Motilin -- an Update
Vol. 35, No. 7, 1984
G. NILAVER, R. DEFENDINI, E.A. ZIMMERMAN, M.C. BEINFELD and T.L. OVDONOHUE, Nature 295 597-598 (I 982). T.L. O'DONOHUE, M.C. BEINFELD, W.Y. CHEY, T.M. CHANG, G. NILAVER, E.A. ZIMMERMAN, H. YAJIMA, H. ADACHI, M. POTH, R.P. McDEVITT and D.M. JACOBOWITZ, Peptides 2 467-477 (1981). J.W. PHILLIS and J.R. KIRKPATRICK, European J. Pharmacol. 58 469-472 (1979). J.W. PHILLIS and J.R. KIRKPATRICK, Can. J. Physiol. Pharmacol. 58 612-623 (1980). V. CHAN-PALAY, M. ITO, P. TONGROACH, M. SAKURAI and S. PALAY, Pro. Natl. Aead. Sci. 79 3355-3359 (1982). J.E.T. FOX, E.E. DANIEL, J. JURY, A.E. FOX and S.M. COLLINS, Life Sci. 33 817-825 (1983). J.E.T. FOX, E.E. DANIEL, J. JURY and H. ROBOTHAM, Life Sci. (1984) (in print). M.A. COOK, K. KOWALEWSKI and E.E. DANIEL, Mater Med. Pol. (Engl. Ed.) 9 113-117 (1977). T. SEGAWA, N. NAKANO, Y. KAI, H. KAWATANI and H. YAJIMA, J. Pharmacol. 28 650 (1976). T. SEGAWA, M. NAKAMO, Y, KAI, H. KAWATANI and H. YAJIMA, J. Pharmacol. 28 650-651 (1976). H. ADACHI, N. TODA, S. HAYASHI, M. NOGUCHI, T. SUZUKI, K. TORIZUKA, H. YAJIMA and K. KOYAMA, Gastroenterology 80 783-788 (1981). J. RIEMER, K. KOLLING and C.J. MAYER, Pflugers Arch. 372 243-250 (1977). L. BUENO, J. FIORAMONTI, V. RAYNER and Y. RUCKEBUSCH, Gastroenterology 82 1395-1402 (1982). H.S. ORMSBEE III, G.L. TELFORD and G.R. MASON, Am. J. Physiol. 237 E451-E456 (I 979). S. SARNA, C. STODDARD, L. BELBECK and D. McWA~E, Am. J. Physiol. 241 616-(]23 (1981). S. SARNA, R.E. CONDON and V. COWLES, Am. J. Physiol. 245 G217-G220 (1983). E.E. DANIEL, T. GONDA, T. DOMOTO, M. OKI and N. YANAIHARA, Can. J. Physiol. Pharmaeol. 60 830-840 (1982). G.L. TELFORD and J.H. SZURSZEWSKI, Gastroenterologie Clin, Biol. 7 717-718 (1983). I. TAKAHASHI, T. SUZUKI, I. AIZAWA and Z. ITOH, Gastroenterology 82 419-424 (1982). I.S. POMERANZ, J.S. DAVISON and E.A. SHAFFER, Dig. Dis. Sci. 28 539-544 (1983). J.C. BROWN, L.P. JOHNSON and D.F. MAGEE, Gastroenterology 50 333-339 (I 965). J.R. DRYBURGH and J.C. BROWN, Gastroenterology 68 1169-1176 (1975). K.Y. LEE, W.Y. CHEY, H.H. TAI and H. YAJIMA, Dig. Dis. 23 789-795 (1978). P. MITZNEGG, S.R. BLOOM, N. CHRISTOFIDES, H. BESTERMAN, W. DOMSCHKE, S. DOMSCHKE, E. WUNSCH and L. DEMLING, Scand. J. Gastroenterol. 11 (Suppl. 39) 53-56 (1976). P. MITZNEGG, S.R. BLOOM, W. DOMSCHKE, S. DOMSCHKE, E. WUNSCH and L. DEMLING, Lancet I 888-889 (1976). S.M. COLLINS, ~.D. LEWIS, J.E.T. FOX, N.S. TRACK, M.M. MEGHJI and E.E. DANIEL, Can. J. Physiol. Pharmacol. 59 188-194 (1981). J.E.T. FOX, N.S. TRACK and E.E. DANIEL, Can. J. Physiol. Pharmacol. 59 180-181 (1981). T.D. LEWIS, S.M. COLLINS, J.E.T. FOX and E.E. DANIEL, Gastroenterology 77 1217-1224 (1979). I.M. MODLIN, P. M I T Z ~ G G and S.R. BLOOM, Gut 19 399-402 (1978). S. SAITO, T. OGAWA, H. SAITO, K. ISHIMARU, I. OSHIMA and Y. SONAKA, Endocrinol. Japou. S.R. 157-162 (1980).
Vol. 35, No. 7, 1984
56. 57. 58. 59. 60. 61.
62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86.
Motilln -- an Update
705
W. DOMSCHKE, G. LUX, P. MITZEGG, S. NEEB, U. STROWZ and S. DOMSCHKE, Gastroenterology 76 1123 (1979). F. AREOLA-ORTIZ, S.R. T. SVENBERG, N.D. CHRISTOFIDES, M.L. FITZPATRICK, BLOOM and R.B. WELBOURN, Gut 23 1024-1028 (1982). Z. ITOH, S. TAKEUCHI, I. AIZAWA, K. MORI, T. TAMINATO, Y. SEINO, H. IMURA and N. YANAIHARA, Dig. Dis. 23 929-935 (1978). G. VANTRA?PEN, J. JANSSENS, T.L. PEETERS, S.R. BLOOM, N.D. CHRISTOFIDES and J. HELLEMANS, Dig. Dis. Soi. 24 497-500 (1979). E.E. DANIEL, J,E.T. FOX, S . M . COLLINS, T.D. LEWIS, M. MEGHJI and N.S. TRACK, Can. J. Physiol. Pharmacol. 59 173-179 (1981). I. TAKAHASHI, R. HONDA, W.J. DODDS, S. SARNA, J. TOOULI, Z. ITOH, W.Y. C~Y, W.J. HOGAN, D. GREIFF and K. BAKER, Am. J. Physiol. _8 G476-G491 (I 983). J.P. MIOLAN and C. ROMAN, Am. J. Physiol. 235 E366-E373 (1978). K.E. HALL, T.Y. EL-SHARKAWY and N.E. DIAMANT, Am. J. Physiol. G276-G284 ( 1982 ). J.E.T. FOX, E.E. DANIEL, J. JURY, N.S. TRACK and S. CHIU, Can. J. Physiol. Pharmacol. 61 1042-1049 (1983). K.Y. LEE, T. CHANG and W.Y. CHEY, Life Sei. 29 1093-1097 (1981). K.E. HALL, G.R. GREENBERG, T.Y. EL-SHAR KAWY and N.E. DIAMANT, Gastroenterology (in press). P. POITRAS, J.H. STEINBACH, G. VanDEVENTER, C.F. CODE and J.H. WALSH, Am. J. Physiol. 239 G215-G220 (1980). S. SARNA, W. CHEY, R. CONDON, W. IX)DIE, T. MEYERS and T. CHANG, Gastroenterologie Clin. Biol. 7 717 (I 983). S. SARNA and R.E. CONDON, Gastroenterologie Clin. Biol. _7 721 (1983). K.E. HALL, G.R. GREENBERG, T.Y. EL-SHARKAWY and W.E. DIAMANT, Can. J. Physiol. Pharcol. 61 1289-1298. P. THOR, K. KROL, S.J. KONTUROK, D.H. COY and A. V. SCHORLY, Am. J. Physiol. 235 E249-E254 (1978). T.L. PEETERS, G. VANTRAPPEN and J. JANBSENS, Gastroenterology 79 716-719 (1980). J. JANSSENS, G. VANTRAPPEN and T.L. PEETERS, Regulatory Peptides 6 363-369 (1983). F . B . KEANE, E.P. DiMAGNO, R.R. DOZOIS and V.L. GO, Gastroenterology 78 310-316 (1980). R . B . SCOTT, S.M. STRASBERG, T.Y. EL-SHARKAWY and N.E. DIAMANT, J. Clin. Invest. 71 644-654 (1983). R.B. SC'-OTT, S.M. STRASB ERG, T.Y. EL-SHARKAWY and N . E . DIAMANT, Gastroenterology (in press). G. LUX, J. FEMPPEL, P. LEDERER, W. ROSCH and W. DOMSCHKE, Acta Hepato-Gastroenterol. 26 166-169 (I 979). K. SJOLUND, G. SANDI'-N, R. HAKANBON and F. SUNDLER, Gastroenterology 85 1120-1130 (1983). T. BORODY, D. BYRNES, J. SLOWIACZEK and D. TITCHEN, Horm. Metab. Res. 35 417-420 (1981). J. PINNINGTON and D.L. WINGATE, J. Physiol. (London) 337 471-478 (1983). M.G. SAIR, K.A. KELLY and V.L. GO, Dig. Dis. Soi. 28 249-256. K.Y. LEE, T.M. CHANG and W.L. CHEY, Am. J. Physiol. 245 G547-G553 (1983). I. TAKAHASHI, W.J. DODDS, H. AMMON, W.J. HOGAN and K. MATHENY, Gastroenterology 84 1329 (1984). R . W . REDINGER, A.M. MORELLO and W.W. LA MORTE, Gastroenterology 80 1259 (1981). S. SARNA, W.Y. CHEY, R.E. CONDON, W.J. DODIE, T. MYERS and T.A. CHANG, Am. J. Physiol. 245 G277-G284 (1983). J.H. STEINBACK and C.F. CODE, in Gastrointestinal Motility, edited by J. Christensen, pp. 247-252, Raven Press, New York (1980).
706
87. 88. 89. 90.
91. 92. 93. 94.
Motilin -- an Update
Vol. 35, No. 7, 1984
H.S. BESTERMAN, N.D. CHRISTOFIDES, P.D. WELSBY, T.E. ADRIAN, D.L. SARSON and S.R. BLOOM, Gut 24 665-671 (1983). H.S. BESTERMAN, S.R. BLOOM, N.D. CHRISTOFIDES, C.N. MALLINSON, A. PERA and R. MODIGLIANI, Gut 19 988-989 (1978). H.S. BESTERMAN, G.C. COOK and D.L. SARSON, Br. Med. J. 2 1252-1255 (1979). H.S. BESTERMA N, T.E. ADRIAN, C.N. MALLINSO N, N.D. CHR ISTOFIDES, D.L. SARSON, A. PERA, L. LOMBARDO, R. MODIGLIANI and S.R. BLOOM, Gut 23 854-861 (1982). S. FUJIMOTO, M. MIYAZAKI, H. ISHIGAMI, Y. TSORUTA and K. OKUI, Acta Chit. Stand. 148 33-37 (1982). K. SHIMA~ A. TANAKA, N. SAWAZAKI, J. HAMABE, R. TANAKA, Y. KOMAHARA and N. YANAIHARA, Horm. Metab. Res. 11 320-321 (1979). W.D. REES, R.J. [SIGH, W.D. CHRISTOFIDES, S.R. BLOOM and L.A. TURNBERG, Gastroenterology 83 575-580 (I 982). R. KLAPDON and E. HAMMER, Klin. Woehenschr. 61 251-253 (1983).