Cyclooxygenase-2 Inhibition Improves Vascular Endothelial Dysfunction in a Rat Model of Endotoxic Shock:Role of Inducible Nitric-Oxide Synthase and Oxidative Stress

摘要

We investigated whether cyclooxygenase(COX)isoforms(COX-1 and COX-2)and decreased NO availability contribute to endothe-lial dysfunction in endotoxemic rats.The involvement of reactive oxygen species(ROS)was also evaluated.Rats were injected with Salmone//a-derived lipopolysaccharide or saline.After 6 h,endo-thelial function of mesenteric resistance arteries was evaluated.In controls,acetylcholine(ACh)-induced relaxation was inhibited by the nitric-oxide synthase inhibitor N~G-monomethyl-L-arginine(L-NMMA)and unaffected by 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)-phenyl-2(5H)-furanone(DFU)(COX-2 inhibitor).In lipopolysaccharide(LPS)-treated rats,the response to ACh was blunted compared with controls,less sensitive to L-NMMA,and enhanced by DFU.COX-2 blockade also improved the inhibitory effect of L-NMMA on cholinergic relaxation.SC-560 [5-(4-clorophenyl)-1-(4-metoxyphenyl)-3-trifluoromethylpirazole](COX-1 inhibitor)did not modify the response to ACh in both groups.LPS-induced endothelial dysfunction was unaffected by the thromboxane A_2(TxA_2)receptor antagonist SQ-29548(7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-[1S(1alpha,2alpha(Z),3alpha,4alpha)]-5-heptenoic acid).In vivo inducible nitric-oxide synthase(iNOS)inhibition by S-methylisothiourea partly attenuated LPS-induced endothelial dysfunction.The antioxidants ascorbic acid and superoxide dis-mutase normalized endothelium-dependent relaxation and restored the inhibitory action of L-NMMA on ACh.Responses to sodium nitroprusside were similar in both groups.In LPS-treated rats,reverse transcription-polymerase chain reaction showed a marked increase in mesenteric iNOS and COX-2 expressions,whereas endothelial nitric-oxide synthase and COX-1 were unchanged.LPS-induced COX-2 overexpression was reduced but not abrogated by S-methylisothiourea.LPS-induced COX-2 up-regulation was also documented by immunohistochemistry.In conclusion,mesenteric resistance vessels from endotoxemic rats show impaired endothelial function due to reduced NO availability,a condition that is partly ascribable to an iNOS-dependent enhanced COX-2 expression,whereas TxA_2 does not seem to be involved.Oxidative stress is the main mechanism responsible for reduced NO availability,and COX-2 might act as a source of ROS.