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Vol. 297, Issue 3, 940-945, June 2001
Department of Experimental and Clinical Pharmacology,
Karl-Franzens-University of Graz, Graz, Austria (E.B., R.S., B.A.P.);
and Department of Microbiology and Immunology, the University of Texas
Medical Branch, Galveston, Texas (A.K.C., D.A.R.)
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.
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