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Effect of Ondansetron on Salmonella typhimurium-Induced Net Fluid Accumulation in the Pig Jejunum in vivo
Comp. Biochem. Physiol. Vol. 118A, No. 2, pp. 297–299, 1997 Copyright 1997 Elsevier Science Inc.
ISSN 0300-9629/97/$17.00 PII S0300-9629(96)00308-8
Effect of Ondansetron on Salmonella typhimuriumInduced Net Fluid Accumulation in the Pig Jejunum in vivo Gerda Majgaard Jensen,1 Marie Louise Grøndahl,1 Carsten Grøndahl Nielsen,2 Erik Skadhauge,1 John Elmerdahl Olsen,3 and Mark Berner Hansen1 1
Department of Physiology and Anatomy, 2 Department of Surgery, and 3 Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, Bu¨lowsvej 13, DK-1870 Frederiksberg C, Denmark
ABSTRACT. Two major pathophysiological mechanisms explaining the diarrhoea induced by Salmonella typhimurium have been suggested to be: (a) invasion of the intestine by the bacteria, and (b) an enterotoxin resembling Vibrio cholerae toxin. Cholera toxin is a potent secretagogue in pig small intestine and induces secretion partly by activating 5-hydroxytryptamine receptors, following release of 5-hydroxytryptamine. Ondansetron is a selective 5-hydroxytryptamine-3 receptor antagonist, which reduces the cholera toxin-evoked fluid accumulation in pig jejunum. The aim of this study was to investigate the effect of ondansetron on Salmonella typhimurium– induced fluid accumulation in ligated loops of pig jejunum in vivo. 1010 colony-forming units of the bacteria was injected into loops and incubated for 8 hr. 200 mg 3 kg21 ondansetron given subcutaneously reduced the Salmonella typhimurium-induced fluid accumulation by about 40%. This result suggests the involvement of 5-hydroxytryptamine and 5-hydroxytryptamine-3 receptors in Salmonella typhimurium-induced diarrhoea. comp biochem physiol 118A;2:297–299, 1997. 1997 Elsevier Science Inc. KEY WORDS. Diarrhoea, 5-hydroxytryptamine, intestinal secretion, jejunum, ondansetron, pig, Salmonella typhimurium
INTRODUCTION Diarrhoea induced by Salmonella typhimurium (ST) is a problem for human health. The pathophysiological mechanisms behind the diarrhoea seems to be multiple, but two main theories exists: (a) diarrhoea is induced by host-derived inflammatory products liberated by invasion of the intestine by the bacteria (16,22,24) and (b) diarrhoea is induced by a cell-free supernatant or enterotoxin without invasion (7,19). The enterotoxin has been characterised and shows immunological and physiological similarities with cholera toxin (CT), suggesting similar mechanisms of action (5,7). CT induces the release of 5-hydroxytryptamine (5-HT) (20), which activates the 5-HT3 receptor in its secretory response (2,12,14). The 5-HT3 receptor is present on the terminal knobs of the enteric neurones (9,10). Ondansetron is a selective antagonist of the 5-HT 3 receptor (4) and has been shown to reduce CT-induced hypersecretion in rats (3) and pigs (11). Address reprint requests to: Mark Berner Hansen, Department of Anatomy and Physiology, The Royal Veterinary and Agricultural University, Bu¨lowsvej 13, DK-1870 Frederiksberg C, Denmark. Tel. 45-3-528-2523; Fax 453-528-2525. Received 29 May 1996; accepted 31 May 1996.
This study evaluates the ability of ondansetron to reduce net fluid accumulation induced by ST in pig jejunum in vivo.
MATERIALS AND METHODS Operative Procedure Nine-week-old female Danish Landrace/Yorkshire pigs (18–20 kg) were used. The pigs were without any present or previous detectable Salmonella infection, as ensured by no specific serum antibodies and no stool-contents of the bacteria. The procedure was the same in all experiments. The pigs were sedated by inhalation of isoflurane (Forene, Abbott) and general anaesthesia was induced by intravenous injection of propofol (Diprivan 10 mg 3 ml21, Zeneca) and maintained throughout the experiment by intubation and inhalation of isoflurane via a semi-closed circle system. At the incision line a long-acting local analgesic (Bupivacaine, Marcain 0.5%) was infiltrated in the skin and underlying tissues to ensure total analgesia. Throughout the experiment the condition of the animal was monitored by measuring temperature, venous pCO2 , rate of heartbeat, and arterial systolic blood pressure. Supporting treatments included a continuous intravenous infusion of Ringer-acetate liquid
G. M. Jensen et al.
298
(160 ml 3 hr21, mmol 3 l21: mmol 3 l21 : Na 1 130; K 1 4; Ca21 2; Mg21 1; Cl2 112 and Ac2 30) and artificial controlled respiration (rate 12 3 min21, vol. 10 ml 3 kg21 and 200 ml O2 3 min21 ).
TABLE 1. Effect of ondansetron (200 mg 3 kg 21 ) on Salmo-
nella typhimurium –induced net fluid accumulation in ligated jejunal loops of the pig.
Loop Content
Experimental Procedure Ten ml of saline was injected subcutaneously before surgery and again after 6 hr. Isolated and ligated jejunal loops were prepared (15). In random order each loop was injected with 10 ml of Argenzio-4 test solution (1) (mmol 3 l21 : Na1 115; K1 10; Cl2 80; HCO3 45; D-glucose 80; pH 7.4) containing ST phag. T12 33 89-1, 1010 colony forming units (cfu) pr. loop (S1010 ), test solution alone (T) or left unfilled (U). After filling, the loops were returned to the peritoneal cavity, and the abdomen was closed. After 8 hr loops were removed. CONTROLS.
The animals were injected subcutaneously with 10 ml of saline containing ondansetron (200 µg 3 kg21 ) (MW 5 366, Glaxo, Middlesex, UK) before surgery and again after 6 hr. Loops were prepared and in random order injected with 10ml of Argenzio-4 test solution containing S1010; test solution alone (T) or left unfilled (U). The loops were returned to the peritoneal cavity and removed after 8 hr. After removal, the loops were weighed immediately, with and without the fluid contents. The difference expressed the net fluid content. Loops were emptied of fluid by gently squeezing following a transverse incision, and then dried to constant weight. A higher content of fluid in loops compared to control loops is termed net fluid accumulation without implying increased fluid secretion and/or reduced fluid absorption. The net fluid accumulation is given as mg fluid content 3 mg dry loop21. ONDANSETRON-TREATED.
STATISTICS Results (net fluid accumulation) are expressed as the means 6 S.E.M. Data were analysed based on all loops tested, n 5 number of loops and N 5 number of animals, and comparisons made by unpaired Student’s t-test assuming that all data, both control and experimental, came from normal distribution. Probability values (P) of 0.05 and less were considered significant. RESULTS (Table 1) Comparing loops containing test-solution alone (T) with unfilled loops (U) in controls and ondansetron-treated, we did not find any significant differences, indicating that the test-solution alone was totally absorbed and did not change net fluid movement in loops. Nor was there any difference in the accumulated amounts in U and T control loops compared to U and T loops from the ondansetron-treated, re-
S10 10 U T
Controls x¯ 6 SEM 5.16 6 0.56* (12) 0.12 6 0.04 (8) 0.10 6 0.03 (8)
OndansetronTreated x¯ 6 SEM 3.08 6 0.35** 0.12 6 0.03 0.13 6 0.02
(30) (10) (10)
Data are expressed as mg fluid accumulated 3 mg dry loop 21 pr. 8 hr. Total number of observations (loops) are indicated in parentheses. Numbers of animals in both the control and ondansetron-treated group was 5. *P # 0.001 as compared to T loops, **P # 0.0001 as compared to T loops. P # 0.005 as compared to controls. U; unfilled. T; test solution alone. S1010; test solution containing 10 10 colony forming units of Salmonella typhimurium.
spectively, indicating that ondansetron did not alter basal net fluid transport. In both controls and ondansetron-treated animals, ST induced a significant fluid accumulation, as S1010 loops were compared to T loops. Furthermore, ondansetron reduced the fluid accumulating effect of S1010 significantly by about a 40%, as S1010 loops from control experiments were compared to the same type of loops in ondansetron-treated animals. DISCUSSION The strain of ST used in the present study was able to induce net fluid accumulation under the chosen experimental conditions, either by reducing absorption or by increasing secretion or both. With this experimental setup, it is not possible to define the exact mechanism. For the induction of diarrhoea by ST, mucosal damage or invasion is not essential (23,24). The mechanism behind ST diarrhoea has been suggested to be the effect of the CTlike Salmonella toxin, since cell-free sterile culture filtrates (CFSC) of ST contains a component, which show similarities with CT immunologically (7) and induces fluid accumulation in rabbit intestinal loops (6). Furthermore, CT-gene-like structures are present in ST (5). Though Salmonella antiserum can neutralise the secretory effect of Salmonella enterotoxin, it fails to neutralise the secretory effect of CT. Furthermore, antiserum to CT does not neutralise the effect of the Salmonella enterotoxin (17,18). This may be explained by the fact that the mode of action of Salmonella CFSC is dependent on the subtype and growth conditions of the bacteria (21). In the present study, ondansetron was able to reduce the ST-induced net fluid accumulation by about 40%. CT acts partly via release of 5-HT from the enterochromaffin cells, the neurones of the enteric nervous system and from mast cells in the submucosa (8). A number of different intestinal 5-HT receptors has been identified, and among them the
Salmonella and 5-Hydroxytryptamine
5-HT 3 receptor. The 5-HT3 receptor is involved in CT-induced net fluid accumulation in pig jejunum (13) and a specific 5-HT3-antagonist, ondansetron, has been shown to reduce both 5-HT and CT-induced hypersecretion (3). These results indicate that ST acts via an ondansetron-sensitive mechanism. Bearing in mind the specific inhibition of the 5-HT 3 receptor by ondansetron, 5-HT and the 5-HT3 receptor seems involved in the pathogenesis of ST-induced diarrhoea. This does not go against the theory about ST inducing intestinal secretion through a CT-like toxin. This work was supported by the Danish Agricultural and Veterinary Research Council, the Leo Research Foundation, and the Velux (1981) Foundation. The authors thank Iben Thomsen, Birgitte Holle, and Bent Nielsen for excellent assistance with experiments and Tina Otto and Dennis Jensen for their skilled handling of animals.
References 1. Argenzio, R.A. Glucose-stimulated fluid absorption in the small intestine during the early stage of swine dysentery. Am. J. Vet. Res. 41:2000 –2006;1980. 2. Beubler, E.; Horina, G.; 5-HT2 and 5-HT3 receptor subtypes mediate cholera toxin-induced intestinal fluid secretion in the rat. Gastroenterology 99:83–89;1990. 3. Buebler, E.; Schirgi-Degen, A.; Gamse R. Inhibition of 5-hydroxytryptamine- and enterotoxin-induced fluid secretion by 5-HT receptor antagonists in the rat jejunum. Eur. J. Pharm.—Env. Tox. Pharm. Sect. 248:157–162;1993. 4. Butler, A.; Hill, J.M.; Ireland, S.J.; Jordan, C.C.; Tyers, M.B. Pharmacological properties of GR38032F, a novel antagonist at 5-HT3 receptors. Br. J. Pharmacol. 94:397–412;1988. 5. Chopra, A.K.; Peterson, J.W.; Houston, C.W.; Pericas, R.; Prasad, R. Enterotoxin-associated DNA sequence homology between Salmonella species and Escherichia coli. FEMS Microbiol. Lett. 77:133–138;1991. 6. Duebbert, I.E.; Peterson, J.W. Enterotoxin-induced fluid accumulation during experimental salmonellosis and cholera: Involvement of prostaglandin synthesis by intestinal cells. Toxicon 23:157–172;1985. 7. Finkelstein, R.A.; Marchlewicz, B.A.; McDonald, R.J.; Boesman-Finkelstein, M.B. Isolation and characterization of cholera-related enterotoxin from Salmonella typhimurium. FEMS Microbiol. Lett. 17:239–241;1983. 8. Forsberg, E.J.; Miller, R.J. Regulation of serotonin release from rabbit intestinal enterochromaffin cells. J. Pharmacol. Exp. Ther. 227:755–765;1983. 9. Frieling, T.; Cooke, H.J.; Wood, J.D. Serotonin receptors on submucous neurons in guinea pig colon. Am. J. Physiol. 261: G1017–G1023;1991. 10. Gershon, M.S.; Wade, P.R.; Kirchgessner, A.L.; Tamir, H. 5HT receptor subtypes outside the central nervous system. Roles in the physiology of the gut. Neur. Psychopharm. 3: 385–395;1990.
299
11. Grøndahl, M.L.; Jensen, G.M.; Skadhauge, E.; Hansen, M.B. Effect of 5-hydroxytryptamine on cholera toxin-induced fluid hypersecretion in porcine jejunum. Eur. J. Physiol. Suppl. 430(4):R88;1995. (Abstract) 12. Hansen, M.B.; Jaffe, B.M. Involvement of eicosanoids and inositol 1,4,5-triphosphate in serotonin-induced secretion in rat intestine in vivo. Comp. Biochem. Physiol. 105C:77–82; 1993. 13. Hansen, M.B.; Skadhauge, E. Ketanserin and granisetron reduce cholera toxin-induced hypersecretion in pig jejunum. Scand. J. Gastroenterol. 29:908–915;1994. 14. Kirchgessner, A.L.; Tamir, H.; Gershon, M.D. Identification and stimulation by serotonin of intrinsic sensory neurons of the submucosal plexus of the guinea pig gut: Activity-induced expression of Fos immunoreactivity. J. Neurosci. 12:235–248; 1992. 15. Lange, S.; Lo¨nnroth, I.; Skadhauge, E. Effects of the antisecretory factors in pigs. Pflu¨gers Arch. 409:328–332;1987. 16. Lodge J.; Douce, G.R.; Amin, I.I.; Bolton, A.J.; Martin, G.D.; Chatfield, S.; Dougan, G.; Brown, N.L.; Stephen, J. Biological and genetic characterization of TnphoA mutants of Salmonella typhimurium TML in the context of gastroenteritis. Infect. Immun. 63:762–769;1995. 17. Rahman, H.; Singh, V.B.; Sharma, V.D.; Harne, S.D. Salmonella cytotonic and cytolytic factors: their detection in Chinese hamster ovary cells and antigenic relatedness. Vet. Microbiol. 31:379–387;1992. 18. Rahman, H.; Singh, V.B.; Sharma, V.D. Purification and characterization of enterotoxic moiety present in cell-free culture supernatant of Salmonella typhimurium. Vet. Microbiol. 39:245–254;1994. 19. Sandefur, P.D.; Peterson, J.W. Notes: Neutralization of Salmonella toxin-induced elongation of chinese hamster ovary cells by cholera antitoxin. Infect. Immun. 15:988–992;1977. 20. Schwo¨rer, H.; Katsoulis, S.; Racke, K. Histamine inhibits 5hydroxytryptamine release from the porcine small intestine: Involvement of 5-HT3 receptors. Gastroenterology 102:1906– 1912;1992. 21. Sobeh, F.Y.; Vadehra, D.N. Enterotoxin production by Salmonella enteritidis at various environmental conditions. Indian J. Med. Res. 78:170–176;1983. 22. Wallis, T.S.; Starkey, W.G.; Stephen, J.; Haddon, S.J.; Osborne, M.P.; Candy, D.C.A. Enterotoxin production by Salmonella typhimurium strains of different virulence. J. Med. Microbiol. 21:19–23;1986. 23. Wallis, T.S.; Hawker, R.J.H.; Candy, D.C.A.; Qi, G.-M.; Clarke, G.J.; Worton, K.J.; Osborne, M.P.; Stephen, J. Quantification of the leucocyte influx into rabbit ileal loops induced by strains of Salmonella typhimurium of different virulence. J. Med. Micribiol. 30:149–156;1989. 24. Worton, K.J.; Candy, D.C.A.; Wallis, T.S.; Clarke, G.J.; Osborne, M.P.; Haddon, S.J.; Stephen, J. Studies on early association of Salmonella typhimurium with intestinal mucosa in vivo and in vitro: Relationship to virulence. J. Med. Microbiol. 29: 283–294;1989.
ISSN 0300-9629/97/$17.00 PII S0300-9629(96)00308-8
Effect of Ondansetron on Salmonella typhimuriumInduced Net Fluid Accumulation in the Pig Jejunum in vivo Gerda Majgaard Jensen,1 Marie Louise Grøndahl,1 Carsten Grøndahl Nielsen,2 Erik Skadhauge,1 John Elmerdahl Olsen,3 and Mark Berner Hansen1 1
Department of Physiology and Anatomy, 2 Department of Surgery, and 3 Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, Bu¨lowsvej 13, DK-1870 Frederiksberg C, Denmark
ABSTRACT. Two major pathophysiological mechanisms explaining the diarrhoea induced by Salmonella typhimurium have been suggested to be: (a) invasion of the intestine by the bacteria, and (b) an enterotoxin resembling Vibrio cholerae toxin. Cholera toxin is a potent secretagogue in pig small intestine and induces secretion partly by activating 5-hydroxytryptamine receptors, following release of 5-hydroxytryptamine. Ondansetron is a selective 5-hydroxytryptamine-3 receptor antagonist, which reduces the cholera toxin-evoked fluid accumulation in pig jejunum. The aim of this study was to investigate the effect of ondansetron on Salmonella typhimurium– induced fluid accumulation in ligated loops of pig jejunum in vivo. 1010 colony-forming units of the bacteria was injected into loops and incubated for 8 hr. 200 mg 3 kg21 ondansetron given subcutaneously reduced the Salmonella typhimurium-induced fluid accumulation by about 40%. This result suggests the involvement of 5-hydroxytryptamine and 5-hydroxytryptamine-3 receptors in Salmonella typhimurium-induced diarrhoea. comp biochem physiol 118A;2:297–299, 1997. 1997 Elsevier Science Inc. KEY WORDS. Diarrhoea, 5-hydroxytryptamine, intestinal secretion, jejunum, ondansetron, pig, Salmonella typhimurium
INTRODUCTION Diarrhoea induced by Salmonella typhimurium (ST) is a problem for human health. The pathophysiological mechanisms behind the diarrhoea seems to be multiple, but two main theories exists: (a) diarrhoea is induced by host-derived inflammatory products liberated by invasion of the intestine by the bacteria (16,22,24) and (b) diarrhoea is induced by a cell-free supernatant or enterotoxin without invasion (7,19). The enterotoxin has been characterised and shows immunological and physiological similarities with cholera toxin (CT), suggesting similar mechanisms of action (5,7). CT induces the release of 5-hydroxytryptamine (5-HT) (20), which activates the 5-HT3 receptor in its secretory response (2,12,14). The 5-HT3 receptor is present on the terminal knobs of the enteric neurones (9,10). Ondansetron is a selective antagonist of the 5-HT 3 receptor (4) and has been shown to reduce CT-induced hypersecretion in rats (3) and pigs (11). Address reprint requests to: Mark Berner Hansen, Department of Anatomy and Physiology, The Royal Veterinary and Agricultural University, Bu¨lowsvej 13, DK-1870 Frederiksberg C, Denmark. Tel. 45-3-528-2523; Fax 453-528-2525. Received 29 May 1996; accepted 31 May 1996.
This study evaluates the ability of ondansetron to reduce net fluid accumulation induced by ST in pig jejunum in vivo.
MATERIALS AND METHODS Operative Procedure Nine-week-old female Danish Landrace/Yorkshire pigs (18–20 kg) were used. The pigs were without any present or previous detectable Salmonella infection, as ensured by no specific serum antibodies and no stool-contents of the bacteria. The procedure was the same in all experiments. The pigs were sedated by inhalation of isoflurane (Forene, Abbott) and general anaesthesia was induced by intravenous injection of propofol (Diprivan 10 mg 3 ml21, Zeneca) and maintained throughout the experiment by intubation and inhalation of isoflurane via a semi-closed circle system. At the incision line a long-acting local analgesic (Bupivacaine, Marcain 0.5%) was infiltrated in the skin and underlying tissues to ensure total analgesia. Throughout the experiment the condition of the animal was monitored by measuring temperature, venous pCO2 , rate of heartbeat, and arterial systolic blood pressure. Supporting treatments included a continuous intravenous infusion of Ringer-acetate liquid
G. M. Jensen et al.
298
(160 ml 3 hr21, mmol 3 l21: mmol 3 l21 : Na 1 130; K 1 4; Ca21 2; Mg21 1; Cl2 112 and Ac2 30) and artificial controlled respiration (rate 12 3 min21, vol. 10 ml 3 kg21 and 200 ml O2 3 min21 ).
TABLE 1. Effect of ondansetron (200 mg 3 kg 21 ) on Salmo-
nella typhimurium –induced net fluid accumulation in ligated jejunal loops of the pig.
Loop Content
Experimental Procedure Ten ml of saline was injected subcutaneously before surgery and again after 6 hr. Isolated and ligated jejunal loops were prepared (15). In random order each loop was injected with 10 ml of Argenzio-4 test solution (1) (mmol 3 l21 : Na1 115; K1 10; Cl2 80; HCO3 45; D-glucose 80; pH 7.4) containing ST phag. T12 33 89-1, 1010 colony forming units (cfu) pr. loop (S1010 ), test solution alone (T) or left unfilled (U). After filling, the loops were returned to the peritoneal cavity, and the abdomen was closed. After 8 hr loops were removed. CONTROLS.
The animals were injected subcutaneously with 10 ml of saline containing ondansetron (200 µg 3 kg21 ) (MW 5 366, Glaxo, Middlesex, UK) before surgery and again after 6 hr. Loops were prepared and in random order injected with 10ml of Argenzio-4 test solution containing S1010; test solution alone (T) or left unfilled (U). The loops were returned to the peritoneal cavity and removed after 8 hr. After removal, the loops were weighed immediately, with and without the fluid contents. The difference expressed the net fluid content. Loops were emptied of fluid by gently squeezing following a transverse incision, and then dried to constant weight. A higher content of fluid in loops compared to control loops is termed net fluid accumulation without implying increased fluid secretion and/or reduced fluid absorption. The net fluid accumulation is given as mg fluid content 3 mg dry loop21. ONDANSETRON-TREATED.
STATISTICS Results (net fluid accumulation) are expressed as the means 6 S.E.M. Data were analysed based on all loops tested, n 5 number of loops and N 5 number of animals, and comparisons made by unpaired Student’s t-test assuming that all data, both control and experimental, came from normal distribution. Probability values (P) of 0.05 and less were considered significant. RESULTS (Table 1) Comparing loops containing test-solution alone (T) with unfilled loops (U) in controls and ondansetron-treated, we did not find any significant differences, indicating that the test-solution alone was totally absorbed and did not change net fluid movement in loops. Nor was there any difference in the accumulated amounts in U and T control loops compared to U and T loops from the ondansetron-treated, re-
S10 10 U T
Controls x¯ 6 SEM 5.16 6 0.56* (12) 0.12 6 0.04 (8) 0.10 6 0.03 (8)
OndansetronTreated x¯ 6 SEM 3.08 6 0.35** 0.12 6 0.03 0.13 6 0.02
(30) (10) (10)
Data are expressed as mg fluid accumulated 3 mg dry loop 21 pr. 8 hr. Total number of observations (loops) are indicated in parentheses. Numbers of animals in both the control and ondansetron-treated group was 5. *P # 0.001 as compared to T loops, **P # 0.0001 as compared to T loops. P # 0.005 as compared to controls. U; unfilled. T; test solution alone. S1010; test solution containing 10 10 colony forming units of Salmonella typhimurium.
spectively, indicating that ondansetron did not alter basal net fluid transport. In both controls and ondansetron-treated animals, ST induced a significant fluid accumulation, as S1010 loops were compared to T loops. Furthermore, ondansetron reduced the fluid accumulating effect of S1010 significantly by about a 40%, as S1010 loops from control experiments were compared to the same type of loops in ondansetron-treated animals. DISCUSSION The strain of ST used in the present study was able to induce net fluid accumulation under the chosen experimental conditions, either by reducing absorption or by increasing secretion or both. With this experimental setup, it is not possible to define the exact mechanism. For the induction of diarrhoea by ST, mucosal damage or invasion is not essential (23,24). The mechanism behind ST diarrhoea has been suggested to be the effect of the CTlike Salmonella toxin, since cell-free sterile culture filtrates (CFSC) of ST contains a component, which show similarities with CT immunologically (7) and induces fluid accumulation in rabbit intestinal loops (6). Furthermore, CT-gene-like structures are present in ST (5). Though Salmonella antiserum can neutralise the secretory effect of Salmonella enterotoxin, it fails to neutralise the secretory effect of CT. Furthermore, antiserum to CT does not neutralise the effect of the Salmonella enterotoxin (17,18). This may be explained by the fact that the mode of action of Salmonella CFSC is dependent on the subtype and growth conditions of the bacteria (21). In the present study, ondansetron was able to reduce the ST-induced net fluid accumulation by about 40%. CT acts partly via release of 5-HT from the enterochromaffin cells, the neurones of the enteric nervous system and from mast cells in the submucosa (8). A number of different intestinal 5-HT receptors has been identified, and among them the
Salmonella and 5-Hydroxytryptamine
5-HT 3 receptor. The 5-HT3 receptor is involved in CT-induced net fluid accumulation in pig jejunum (13) and a specific 5-HT3-antagonist, ondansetron, has been shown to reduce both 5-HT and CT-induced hypersecretion (3). These results indicate that ST acts via an ondansetron-sensitive mechanism. Bearing in mind the specific inhibition of the 5-HT 3 receptor by ondansetron, 5-HT and the 5-HT3 receptor seems involved in the pathogenesis of ST-induced diarrhoea. This does not go against the theory about ST inducing intestinal secretion through a CT-like toxin. This work was supported by the Danish Agricultural and Veterinary Research Council, the Leo Research Foundation, and the Velux (1981) Foundation. The authors thank Iben Thomsen, Birgitte Holle, and Bent Nielsen for excellent assistance with experiments and Tina Otto and Dennis Jensen for their skilled handling of animals.
References 1. Argenzio, R.A. Glucose-stimulated fluid absorption in the small intestine during the early stage of swine dysentery. Am. J. Vet. Res. 41:2000 –2006;1980. 2. Beubler, E.; Horina, G.; 5-HT2 and 5-HT3 receptor subtypes mediate cholera toxin-induced intestinal fluid secretion in the rat. Gastroenterology 99:83–89;1990. 3. Buebler, E.; Schirgi-Degen, A.; Gamse R. Inhibition of 5-hydroxytryptamine- and enterotoxin-induced fluid secretion by 5-HT receptor antagonists in the rat jejunum. Eur. J. Pharm.—Env. Tox. Pharm. Sect. 248:157–162;1993. 4. Butler, A.; Hill, J.M.; Ireland, S.J.; Jordan, C.C.; Tyers, M.B. Pharmacological properties of GR38032F, a novel antagonist at 5-HT3 receptors. Br. J. Pharmacol. 94:397–412;1988. 5. Chopra, A.K.; Peterson, J.W.; Houston, C.W.; Pericas, R.; Prasad, R. Enterotoxin-associated DNA sequence homology between Salmonella species and Escherichia coli. FEMS Microbiol. Lett. 77:133–138;1991. 6. Duebbert, I.E.; Peterson, J.W. Enterotoxin-induced fluid accumulation during experimental salmonellosis and cholera: Involvement of prostaglandin synthesis by intestinal cells. Toxicon 23:157–172;1985. 7. Finkelstein, R.A.; Marchlewicz, B.A.; McDonald, R.J.; Boesman-Finkelstein, M.B. Isolation and characterization of cholera-related enterotoxin from Salmonella typhimurium. FEMS Microbiol. Lett. 17:239–241;1983. 8. Forsberg, E.J.; Miller, R.J. Regulation of serotonin release from rabbit intestinal enterochromaffin cells. J. Pharmacol. Exp. Ther. 227:755–765;1983. 9. Frieling, T.; Cooke, H.J.; Wood, J.D. Serotonin receptors on submucous neurons in guinea pig colon. Am. J. Physiol. 261: G1017–G1023;1991. 10. Gershon, M.S.; Wade, P.R.; Kirchgessner, A.L.; Tamir, H. 5HT receptor subtypes outside the central nervous system. Roles in the physiology of the gut. Neur. Psychopharm. 3: 385–395;1990.
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