Abstract
The mechanisms of diarrhea in Asiatic cholera have been studied extensively. Cyclic AMP, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated in the pathogenesis of cholera. To elucidate the role of the different isoforms (COX-1 and COX-2) of cyclooxygenase in cholera toxin (CT)-induced fluid secretion and intraluminal prostaglandin E2 (PGE2) release in the rat jejunum in vivo, the effects of the COX-2 inhibitors NS-398 ([N-(2-cyclohexaloxy-4-nitrophenyl)methanesulfonamide]) and DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone], and of the COX-1 inhibitor SC-560, were studied. Net fluid transport was measured gravimetrically and PGE2 by radioimmunoassay. COX-1 and COX-2 mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and COX-2 protein by Western blot analysis in mucosal scrapings. CT caused profuse net fluid secretion in all control rats. The COX-2 inhibitors NS-398 and DFU, but not the COX-1 inhibitor SC-560 or dexamethasone, dose-dependently inhibited CT-induced fluid secretion and PGE2 release. RT-PCR showed expression of COX-1 and of COX-2 mRNA in control rats. CT did not induce an increase and dexamethasone did not reduce COX-2 mRNA, whereas lipopolysaccharide caused a marked induction of COX-2 mRNA, which was inhibited by dexamethasone. A weak band of COX-2 protein was observed in controls; however, CT enhanced COX-2 levels, which remained unaffected by dexamethasone. It can be assumed that post-transcriptional modulation is responsible for CT-induced increase in COX-2 protein. COX-1 does not seem to be involved. Therefore, PGE2 produced by COX-2 seems to be responsible for the profuse fluid secretion induced by CT, and COX-2 appears to be a specific target for the treatment of Asiatic cholera.
Footnotes
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Send reprint requests to: Prof. Dr. Eckhard Beubler, Department of Experimental and Clinical Pharmacology, Karl-Franzens-University of Graz, Universitätsplatz 4, A-8010 Graz, Austria. E-mail: eckhard.beubler{at}kfunigraz.ac.at
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This study was supported by the Austrian Scientific Research Funds (No. P 12158-MED and P 13512-MED), the Franz Lanyar Stiftung and a grant from the Crohn's and Colitis Foundation of America.
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Parts of this study were presented at the meeting of the American Gastroenterological Association in the spring of 1999 in Orlando, Florida and in the Proceedings of the Fifth Workshop of the Intestinal Mucosa Function Group of the German Society of Gastroenterology, in press.
- Abbreviations:
- CT
- cholera toxin
- PG
- prostaglandin, COX, cyclooxygenase
- 5-HT
- 5-hydroxytryptamine
- LPS
- lipopolysaccaride
- RT-PCR
- reverse transcription-polymerase chain reaction
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- DFU
- 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone
- TBS
- Tris-buffered saline
- AP
- alkaline phosphatase, bp, base pair
- The American Society for Pharmacology and Experimental Therapeutics
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