564 Gut 1999;45:564–569 The sigma ligand, igmesine, inhibits cholera toxin

and Escherichia coli enterotoxin induced jejunal Gut: first published as 10.1136/gut.45.4.564 on 1 October 1999. Downloaded from secretion in the rat

J L Turvill, P Kasapidis, MJGFarthing

Abstract stimulate the intracellular synthesis of cyclic Background—Cholera toxin, and Es- AMP, while E coli heat stable enterotoxin (STa) cherichia coli heat labile (LT) and heat increases cyclic GMP.2–4 All three enterotoxins stable (STa) enterotoxins induce small additionally promote secretion through activa- intestinal secretion in part by activating tion of the enteric nervous system.5 enteric nerves. Igmesine is a novel sigma Oral rehydration solutions have become the receptor ligand that inhibits neurally mainstay of therapy for such diseases, which mediated secretion. continue to be major causes of morbidity and Aims—To assess the antisecretory poten- mortality worldwide. Although antibiotics such tial of igmesine in cholera toxin, LT, and as tetracycline and the fluoroquinolones can STa induced water and electrolyte secre- reduce the duration and severity of these tion using an in vivo rat model of jejunal illnesses, there is not yet widely available a truly perfusion. antisecretory agent that can pharmacologically Methods—After pretreatment with igmes- inhibit enterotoxin induced secretion and so ine, 0.03–10 mg/kg intravenously, jejunal ameliorate the severity of the diarrhoeal 6–8 segments of anaesthetised, adult male illness. Wistar rats were incubated with cholera In 1976, Martin et al attributed one of the toxin (25 µg), LT (25 µg), or saline. Jejunal three major profiles of opioid associated eVects perfusion with a plasma electrolyte solu- in the dog (canine delirium) to a putative fourth 9 tion containing a non-absorbable marker opiate receptor designated sigma. Later, be- was undertaken. In some cases 200 µg/l cause of its insensitivity to blockade by STa was added to the perfusate. After and its enantioselectivity, it became clear that equilibration, net water and electrolyte the was not a type of opiate movement was determined. In additional receptor. It was declassified and is now consid- http://gut.bmj.com/ experiments rats received igmesine, in- ered as a separate receptor class. Sigma recep- travenously or intrajejunally, after expo- tors are found throughout the central nervous sure to cholera toxin. system, but their function remains unclear. It Results—Cholera toxin induced net water has been proposed that they attenuate the ability secretion was inhibited by 1 mg/kg igmes- of acetylcholine to activate the phosphoinositide second messenger system, possibly by inducing ine (median −120 versus −31 µl/min/g, 10 p<0.001). LT and STa induced secretion the internalisation of cholinergic receptors. In

were also inhibited by 1 mg/kg igmesine 1988, Roman et al presented evidence for the on September 24, 2021 by guest. Protected copyright. existence of sigma sites in guinea pig myenteric (−90 versus −56, p<0.03; and −76 versus 11 −29, p<0.01, respectively). Igmesine re- plexus. Further autoradiographic studies have duced established cholera toxin induced revealed the existence of a dense distribution of secretion. sigma binding sites in the mucosa and submu- cosa of guinea pig intestine.12 Then, in 1989 a Conclusion—The sigma ligand, igmesine, inhibits neurally mediated enterotoxi- functional role for these receptors in modulating genic secretion. Its ability to inhibit estab- intestinal motility was suggested. Campbell et al lished secretion makes it an agent with showed that longitudinal muscle contraction induced by electrical stimulation of myenteric therapeutic potential. (Gut 1999;45:564–569) plexus was blocked by the prototypical sigma ligand, (+)-SKF 10,047.13 This was accompa- Keywords: igmesine; cholera toxin; Escherichia coli nied by the inhibition of acetylcholine release. Digestive Diseases enterotoxin; jejunal secretion Since this initial observation, Pascaud et al and Research Centre, St Bartholomew’s and others have also proposed that sigma ligands The Royal London influence intestinal water and electrolyte School of Medicine The diarrhoeal diseases caused by infection transport.14–16 and Dentistry, Turner with Vibrio cholerae and enterotoxigenic Es- Recently the highly selective sigma ligand, Street, London cherichia coli are characterised by the produc- igmesine (JO 1784, (+)-cinnamyl-1-phenyl- E1 2AD, UK tion of highly potent enterotoxins.1 Binding of 1-N-methyl-N-cyclo-propylene) has been J L Turvill P Kasapidis these enterotoxins to the small intestinal MJGFarthing epithelium results in the activation of cyclic nucleotide second messenger systems which Abbreviations used in this paper: CT, cholera Correspondence to: initiate metabolic cascades characterised by the toxin; 5-HT, 5-hydroxytryptamine; LT, Escherichia coli Dr Turvill. heat labile enterotoxin; NPY, ; PEG, opening of apical chloride channels and the polyethylene glycol 4000; PES, plasma electrolyte Accepted for publication onset of small intestinal secretion. Cholera solution; STa, Escherichia coli heat stable enterotoxin; 14 April 1999 toxin and E coli heat labile enterotoxin (LT) VIP, vasoactive intestinal polypeptide. Igmesine and toxigenic secretion 565

described.17 It is capable of displacing tritiated 25 µg cholera toxin in 2 ml isotonic saline was (+)-SKF 10,047 from brain sites in mice and is instilled into the isolated segment and both

eVective when administered parenterally or cannulae were clamped. After two hours incu- Gut: first published as 10.1136/gut.45.4.564 on 1 October 1999. Downloaded from orally. Furthermore, it seems to have antisecre- bation, the clamps were removed and the jeju- tory properties. Igmesine reverses vasoactive nal perfusion commenced as described above. intestinal polypeptide (VIP) induced increases Intravenous administration of igmesine after in short circuit current in stripped ileal sheets cholera toxin exposure—Rats were incubated mounted in Ussing chambers, and in vivo with 25 µg cholera toxin as described above. studies in mouse and man have showed that After an initial 30 minute period of perfusion to igmesine inhibits prostaglandin induced confirm the onset of secretion, rats intrave- diarrhoea.18 19 nously received 0.3 or 1 mg/kg igmesine in 0.25 As both VIP and prostaglandins have been ml saline or saline alone. The perfusion was implicated as secretagogues in the pathophysi- then extended for a further 30 minutes. ology of enterotoxigenic small intestinal water Luminal administration of igmesine after cholera and electrolyte secretion, we determined toxin exposure—Rats were incubated with 25 µg whether igmesine would inhibit cholera toxin, cholera toxin as described above. Igmesine 40 LT, or STa induced secretion.20 21 An estab- µg/ml was added to the plasma electrolyte per- lished in vivo rat model of small intestinal per- fusion fluid and was present throughout the fusion was used.22 experiment.

Methods LT EXPERIMENTS BASIC EXPERIMENTAL DESIGN Isolated jejunal segments, prepared as de- Adult male Wistar rats (180–220 g body scribed above, were intravenously pretreated weight), fasted for 18 hours with free access to with 1 mg/kg igmesine or saline alone 15 min- water, were anaesthetised with intraperitoneal utes prior to incubation with 25 µg LT in 2 ml sodium pentobarbitone (60 mg/kg) and saline. After two hours in situ jejunal perfusion maintained by interval injections (15–30 mg/ was undertaken to determine net water and kg) as necessary throughout the experiment. electrolyte movement. Body temperature was maintained at 37°C using a heat pad. The abdomen was opened STa EXPERIMENTS through a midline incision and a 20 cm jejunal Isolated jejunal segments were prepared as segment was created by the insertion of a described above. Rats were intravenously proximal cannula into the small intestine 5 cm pretreated with 1 mg/kg igmesine or saline. beyond the duodenojejunal flexure and a Fifteen minutes later in situ small intestinal second cannula 20 cm more distally. Both can- perfusion was undertaken using PES into nulae were ligated as previously described.22 which 200 µg/l STa (equivalent to 50 000 The isolated segment was gently flushed with mouse units) had been added. Net STa http://gut.bmj.com/ isotonic saline (37°C) and air to clear it of induced water and electrolyte movement was residual contents, the intestine was returned to determined. the abdominal cavity, and the abdomen closed. The jejunal segment was then perfused at a MATERIALS rate of 0.5 ml/min with plasma electrolyte Cholera toxin was obtained from the Swiss solution (PES) containing Na 140 mmol/l, K 4 Serum and Vaccine Institute, Berne, and LT

mmol/l, Cl 104 mmol/l, and HCO3 40 mmol/l and STa from Sigma Chemical Company. on September 24, 2021 by guest. Protected copyright. to which 5 g/l polyethylene glycol 4000 (PEG) Radiolabelled polyethylene glycol (14C-PEG and 4 µCi/l of 14C-PEG had been added. Thirty 4000) was obtained from Amersham Inter- minutes were allowed to elapse to ensure national. Igmesine was kindly supplied by establishment of a steady state after which Institut de Recherche Jouveinal, Fresnes, three consecutive 10 minute collections of the France and all other chemicals were supplied eZuent were obtained from the distal cannula. by British Drug House. The samples were stored at −50°C for up to 48 14 hours prior to analysis of C-PEG and electro- ANALYTICAL METHODS lyte concentration. At the end of the experi- 14C-PEG concentrations in the eZuent were ment rats were killed by an overdose of pento- measured in triplicate by liquid scintillation barbitone; the perfused segment was removed, spectroscopy in an LKB Wallac Ultra-beta rinsed, blotted, and desiccated in an oven at 1210 scintillation counter. Mean net fluid 100°C for 18 hours to obtain the dry weight. movement was calculated from three consecu- tive eZuent samples and expressed as µl/min/g BASAL STATE EXPERIMENTS dry intestinal weight. Positive values denote net Fifteen minutes before jejunal perfusion was absorption and negative values net secretion. undertaken, rats were intravenously pretreated Chloride concentration was determined by a with 10 mg/kg igmesine, dissolved in 0.25 ml Corning 925 chloride analyser, and sodium saline, or saline alone. and potassium by flame photometry (Instru- mentation Laboratories 943). Net solute move- CHOLERA TOXIN EXPERIMENTS ment is expressed as µmol/min/g. Three groups of experiments were carried out: Steady state condition was confirmed by less Intravenous administration of igmesine before than 5% variation in net water movement cholera toxin exposure—Rats were intravenously between consecutive 10 minute collections. pretreated with 0.03, 0.1, 0.3, 1, 3 or 10 mg/kg Values were accepted only if 14C-PEG recovery igmesine or saline alone. Fifteen minutes later fell between 95 and 105%.22 23 566 Turvill, Kasapidis, Farthing

Table 1 EVect of intravenous pretreatment with igmesine on cholera toxin induced jejunal net secretion of electrolytes

Igmesine (mg/kg) Net Cl− flux (µmol/min/g) Net Na+ flux (µmol/min/g) Net K+ flux (µmol/min/g) Number Gut: first published as 10.1136/gut.45.4.564 on 1 October 1999. Downloaded from 0.00 −24 (−29 to −17) −27 (−33 to −18) −2.0 (−2.0 to −1.4) 29 0.03 −19 (−21 to −17) −24 (−31 to −17) −1.7 (−1.7 to −1.5) 5 0.10 −17* (−23 to −11) −17* (−27 to −13) −1.5* (−2.0 to −1.2) 19 0.30 −18* (−20 to −15) −14* (−16 to −13) −1.5 (−1.7 to −1.4) 9 1.00 −18* (−20 to 12) −12* (−19 to −10) −1.4* (−1.6 to −1.1) 10 3.00 −16* (−16 to −14) −13* (−17 to −8) −0.9* (−1.0 to −0.6) 8 10.00 −11* (−13 to −9) −16* (−17 to −16) −1.3* (−1.5 to −1.0) 8

Data expressed as median (interquartile range). *p<0.05 compared with cholera toxin (Kruskal-Wallis test).

STATISTICAL ANALYSIS vealed no significant diVerence in antisecretory Results are expressed as median and interquar- eVect above a dose of 0.1 mg (p>0.08). Net tile range in each group of animals studied. electrolyte movement was comparable with net DiVerences in net fluid and electrolyte move- water movement (table 1). ment were examined using the Mann-Whitney test or a non-parametric analysis of variance Intravenous administration of igmesine after (Kruskal-Wallis test with intergroup analysis) exposure to cholera toxin whenever appropriate. Cuzick’s test for trend In keeping with a steady state, jejunal net was applied to appropriate data sets. water secretion did not change during the 30 When assessing the e cacy of igmesine or Y minute collection periods pre- and post-saline placebo in established secretion, data are (median reduction in secretion 17.6% (inter- expressed as percentage change in net fluid quartile range −2.8% to 38.1%), n=32; movement between the first and second p>0.05, Mann-Whitney). An intravenous periods of collection. This corrects for any bolus of 0.3 mg/kg igmesine similarly failed to baseline di erences between groups. Positive V modify the steady state (20.9% reduction percentages reflect reversal of secretion. (−8.8% to 73.3%), n=10). By contrast however, 1.0 mg/kg igmesine significantly Results reduced established cholera toxin induced BASAL STATE EXPERIMENTS jejunal net water secretion (42.4% reduction Basal net jejunal water movement (192.5 in secretion (23.7% to 67.4%), n=12; p=0.04; µl/min/g (149.5–237.8), n=14) was unaVected fig 2). by igmesine (172.9 µl/min/g (132.2–239.9), n=6). Net jejunal electrolyte movement paral- leled net jejunal water movement (control: Cl−, Luminal administration of igmesine after exposure 1.1 µmol/min/g (−2.2 to 2.3); Na+, 16.5 (12.3 to cholera toxin to 18.5); K+, 0.1 (0.0 to 0.1); igmesine: Cl−, 0.8 A highly significant reduction in net water http://gut.bmj.com/ (−2.5 to 1.1); Na+, 17.7 (13.6 to 19.0); K+, 0.1 secretion (57.4% (41.6% to 66.7%), n=8; (−0.1 to 0.1)). p=0.002) occurred after the intrajejunal delivery of 6.0 mg/kg igmesine via the perfusate CHOLERA TOXIN EXPERIMENTS (fig 3). Intravenous administration of igmesine before cholera toxin exposure LT AND STa EXPERIMENTS Cholera toxin produced net water secretion in Both LT and STa induced jejunal net water and on September 24, 2021 by guest. Protected copyright. all rats. Igmesine had an antisecretory eVect at electrolyte secretion in all rats. Pretreatment doses of 0.1, 0.3, 1, 3 and 10 mg/kg (p=0.007; with 1 mg/kg igmesine significantly inhibited fig 1). Although Cuzick’s test for trend was both LT and STa induced jejunal net secretion positive (p<0.0001), intergroup analysis re- of water and electrolytes (fig 4, table 2).

200 Median and IQR 50

0 µ l/min/g)

µ l/min/g dw) 100 –50

–100 0

–150 * * * * –100 † –200 Median † † * Net water movement ( Net water movement ( –250 30 45 60 75 90 –200 Control Igmesine CT 0.03 0.1 0.3 1 3 10 Time (min) Igmesine (mg/kg) Figure 2 EVect of igmesine (1 mg/kg intravenously) on (n = 14) (n = 6) (n = 29) (n = 5) (n = 19) (n = 9) (n = 10) (n = 8) (n = 8) established cholera toxin induced jejunal net water secretion. Net water secretion in individual rats (n=12) is represented Figure 1 EVect of pretreatment with igmesine on cholera toxin (CT) induced jejunal net at 45 minutes (pre-igmesine) and at 75 minutes water secretion. Data expressed as median and interquartile range. *p<0.04 compared with (post-igmesine). p<0.04 compared with cholera toxin alone CT; †p<0.02 compared with CT + 0.03 mg/kg igmesine (Kruskal-Wallis). (Mann-Whitney test). Igmesine and toxigenic secretion 567

40 who found that igmesine inhibits both VIP induced secretion in vitro and prostaglandin

0 induced secretion in humans, respectively. Gut: first published as 10.1136/gut.45.4.564 on 1 October 1999. Downloaded from Riviere et al have also found that igmesine is –40 proabsorptive in unstimulated mouse jejunum, in vitro.16 –80 In a study of rat and mouse brain sigma sites, igmesine was compared with 1,3-di-o- –120 tolyguanidine and , the two com- pounds previously found to have a high affinity –160 Median for the sigma site. Igmesine was more potent than 1,3-di-o-tolyguanidine and similar in Net water movement ( µ l/min/g) –200 aYnity to haloperidol at inhibiting (+)- 30 45 60 75 90 SKF 10,047 binding to sigma sites. Igmesine Time (min) has no significant aYnity for a range of opioid, Figure 3 EVect of the addition of igmesine (40 µg/ml) to muscarinic, adrenergic, dopaminergic, seroton- the perfusate, on established cholera toxin induced jejunal net water secretion. Net water secretion in individual rats (n=8) inergic, histaminergic, and GABAergic binding is represented on equilibration at 45 minutes and after sites.17 It displaces tritiated (+)-SKF 10,047 receiving 6 mg/kg igmesine, intrajejunally, at 75 minutes. from sigma sites in rat and mouse brain with p<0.002 compared with cholera toxin perfused with standard plasma electrolyte solution (Mann-Whitney test). ID50 values in the mouse of 1.2 mg/kg after intraperitoneal administration and 3.5 mg/kg when given orally. The displacement by igmes- Discussion ine is long lasting, with at least 60% inhibition The high aYnity sigma ligand, igmesine, dose of (+)-SKF 10,047 binding at four hours. The dependently inhibits cholera toxin induced ID50 values are comparable with the intra- jejunal net water and electrolyte secretion and venous and intraluminal doses of igmesine reduces established cholera toxin induced required in our study to inhibit enterotoxin secretion when given either as an intravenous induced secretion. bolus or intraluminally, in the perfusate. The Cholera toxin, LT, and STa are thought to maximal antisecretory dose was 1 mg/kg, given induce small intestinal secretion by diVerent intravenously. Igmesine also inhibits LT and mechanisms of action. Cholera toxin and LT STa induced secretion at that dose, but does share a remarkable structural homology. Both not have any eVect on basal water and electro- are composed of a pentameric binding subunit lyte transport. These findings are in keeping 24 and an enzymic subunit. The former attaches with those of Carlisi et al, who showed the to an enterocyte ganglioside (GM ) receptor antisecretory eVect of sigma ligands, and of 1 18 19 which permits the latter to activate irreversibly Rao and colleagues and Roze and colleagues a stimulatory G protein on the basolateral http://gut.bmj.com/ membrane of the enterocyte.125This results in 0 the activation of adenylate cyclase and an Median and IQR increase in intracellular concentrations of cyclic AMP.23Cyclic AMP is thought to initi- ate an intracellular signalling cascade resulting in phosphorylation of apical anion channels –40 ** 26 27 µ l/min/g dw) and eZux of chloride ions. DiVerences on September 24, 2021 by guest. Protected copyright. between the two toxins have been recognised 28–30 however. As well as the GM1 receptor, LT † binds to a glycoprotein receptor which also activates adenylate cyclase.31 In addition, we –80 have recently identified diVerences between the two in the recruitment of the secretagogue and neurotransmitter, 5-hydroxytryptamine (5- HT). Cholera toxin is known to induce the Net water movement ( release of 5-HT from enterochromaYn cells, –120 stimulating secretion via adjacent mucosal LT LT + Igmesine STa STa + Igmesine (n = 16) (n = 9) (n = 8) (n = 16) 5-HT2 receptors and 5-HT3 receptors located on sensory dendrites.32 33 By contrast, LT does Figure 4 EVect of pretreatment with igmesine (1 mg/kg intravenously) on heat labile not induce 5-HT release and is not inhibitable 34 35 (LT) and heat stable (STa) enterotoxin induced jejunal net water secretion. Data expressed by 5-HT2 or 5-HT3 antagonists. STaisa as median and interquartile range. †p<0.03 compared with LT; **p<0.01 compared with smaller toxin, which binds to and activates two STa (Mann-Whitney test). membrane bound cyclic GMP dependent Table 2 EVect of igmesine (1 mg/kg intravenously) on Escherichia coli heat labile (LT) kinases on the cell surface. It initiates a and heat stable (STa) enterotoxin induced jejunal net secretion of electrolytes secretory signalling cascade which is much more rapid in onset than cholera toxin and LT Net Cl− flux Net Na+ flux Net K+ flux (µmol/min/g) (µmol/min/g) (µmol/min/g) Number and is characterised by a rise in intracellular concentrations of cyclic GMP.4 LT −19 (−28 to −17) −20 (−24 to −18) −1.1 (−1.4 to −0.8) 16 LT + igmesine −15* (−18 to −13) −10* (−13 to −5) −0.6* (−0.8 to −0.5) 9 Despite these diVerences, the antisecretory STa −11 (−14 to −10) −18 (−20 to −15) −1.3 (−1.5 to −1.1) 8 eYcacy of igmesine implies a common pathway STa + igmesine −5.3† (−6 to −5) −7.6† (−9 to −6) −0.6† (−0.6 to −0.6) 5 for these enterotoxins, on which the sigma lig- Data expressed as median (interquartile range). and acts. This pathway is likely to involve com- *p<0.02 compared with LT, †p<0.02 compared with STa (Mann-Whitney test). ponents of the enteric nervous system. The role 568 Turvill, Kasapidis, Farthing

of the enteric nervous system in mediating igmesine and NPY acted on diVerent recep- more than 50% of cholera toxin and STa tors. Thus, it now seems untenable that NPY

induced secretion was established by Lundgren and peptide YY act directly by binding to Gut: first published as 10.1136/gut.45.4.564 on 1 October 1999. Downloaded from et al who showed the inhibition of secretion by sigma sites. However, the situation in vivo is tetrodotoxin, lidocaine, and hexamethonium.5 such that sigma agonists and NPY/peptide YY LT has been studied in considerably less depth display very similar eVects. They seem to use but we have confirmed that LT induced secre- some common neural pathway in such a way tion is also inhibitable by neuronal blockade.35 that sigma sites, possibly through an endo- It has been proposed that enterotoxins activate genous ligand, are permissive to the NPY/ a neuronal secretory reflex composed of at least peptide YY eVect. A similar model already

three enteric neurones. The first, a sensory exists as á2 antagonists block the peptide YY neurone, has dendrites extending from the mediated inhibition of the eVect of VIP in rat mucosa and relays information to an interneu- jejunum.40 rone in the submucosal and myenteric plex- In conclusion, the high aYnity sigma ligand, uses. The interneurone then projects to a igmesine, is an eVective antisecretory agent secretomotor eVerent. The interneurone per- against both cholera toxin and the two entero- mits additional enteric and extrinsic neuronal toxins responsible for the majority of cases of inputs to modulate the reflex arc. Acetylcholine travellers’ diarrhoea. Igmesine probably acts and VIP have been implicated as the secretory via a secretory pathway common to all three neurotransmitters of the secretomotor eVerent enterotoxins, which is likely to be neuronal, for both cholera toxin and STa induced involving NPY related mechanisms. The dem- secretion.5 As sigma ligands inhibit VIP onstration by Roze et al that igmesine strongly

induced secretion and attenuate the actions of inhibits prostaglandin E2 induced secretion in acetylcholine, modulation of this limb of the human volunteers confirms the tolerability and neuronal arc may represent the common path- eYcacy of this agent in a clinical setting.19 The way by which igmesine acts. Evidence for this broad antisecretory eVect of igmesine and its comes, firstly, from the fact that sigma ability to reduce established secretion by over receptors are located in the myenteric plexus, 50% make it a drug with the promise of thera- the mucosa, and the submucosa of guinea pig peutic potential. small intestine.11 12 Secondly, the proabsorptive eVects of sigma ligands are neurally mediated. The authors gratefully acknowledge the receipt of an edu- Riviere et al have showed that sigma ligands, cational grant from Institut de Recherche Jouveinal, Fresnes, including igmesine, induce a sustained de- France. crease in short circuit current in mouse 1 Spangler BD. Structure and function of cholera toxin and jejunum, in vitro, without eVecting tissue the related Escherichia coli heat labile enterotoxin. conductance.16 This is prevented by the neural Microbiol Rev 1992;56:622–47.

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common secretomotor pathway for cholera on September 24, 2021 by guest. Protected copyright. Dis Sci 1989;34:264–83. toxin, LT, and STa. NPY exhibits similar 6 Walker-Smith JA. Gastroenteritis and its sequelae. In: antisecretory properties to sigma ligands.16 It is Walker-Smith JA, Murch S, eds. Diseases of the small intestine in childhood. 4th edn. London: Isis Medical Media a potent inhibitor of VIP induced secretion Ltd, 1999:119−94. and, like igmesine, inhibits both cholera toxin 7 Bennish ML. Cholera: pathphysiology, clinical features and 36 37 treatment. In: Wachsmuth IK, Blake PA, Olsvik O, eds. and STa induced secretion. An identical Vibrio cholerae and cholera: molecular to global perspectives. pharmacological profile for NPY and sigma Washington DC: American Society for Microbiology, 1994:229–55. ligand stimulated duodenal alkaline secretion 8 Gotuzzo E, Seas C, Echevarria J, et al. Ciprofloxacin for the in the rat has been described. As a result it has treatment of cholera: a randomized, double-blind, control- led clinical trial of a single daily dose in Peruvian adults. been proposed that the endogenous peptides, Clin Infect Dis 1995;20:1485–90. NPY and PYY act through neuronal sigma 9 Martin W, Eades C, Thompson J, et al. The eVects of 14 morhine- and nalorphine-like drugs in the nondependent binding sites. and morphine-dependent chronic spinal dog. J Pharmacol While the endogenous ligand for the sigma Exp Ther 1976;197:517–32. 10 Walker JM, Bowen WD, Walker FO, et al. Sigma receptors: receptor has yet to be identified, Roman et al biology and function. Pharmacol Rev 1990;42:355–402. have reported that NPY and the related 11 Roman F, Pascaud X, Vauche D, et al. Evidence for a non- opioid sigma binding site in the guinea-pig myenteric peptide YY have a high aYnity for rat brain plexus. Life Sci 1988;42:2217–22. sigma receptors and that the distribution of 12 Roman F, Pascaud X, Chomette G, et al. Autoradiographic localization of sigma opioid receptors in the gastrointestnal NPY corresponds well with the distribution of tract of the guinea pig. Gastroenterology 1989;97:76–82. sigma receptors.38 Ta m et al have been unable 13 Campbell BG, Scherz MW, Keana JFW, et al. Sigma recep- 39 tors inhibit contractions of the guinea pig ileum longitudi- to confirm this observation however. Further- nal muscle/myenteric plexus preparation elicited by both more, when Rao et al assessed the eYcacy of electrical stimulation and exogenous serotonin. J Neurosci 1989;9:3380–91. igmesine and NPY in reversing VIP induced 14 Pascaud X, Chovet M, Roze C, et al. Neuropeptide Y and mouse ileal ion transport it was found that the sigma receptor agonists act through a common pathway to stimulate duodenal alkaline secretion in rats. Eur J addition of VIP antagonists significantly re- Pharmacol 1993;231:389–94. duced the eVects of VIP and igmesine but not 15 Riviere PJ, Pascaud X, Junien JL, et al. Neuropeptide Y and 18 JO 1784, a selective sigma ligand, alter intestinal transport of NPY. It was concluded that although sigma through a common, haloperidol-sensitive site. Eur J receptors suppress the action of released VIP, Pharmacol 1990;187:557–9. Igmesine and toxigenic secretion 569

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