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AIM: The present study was aimed to examine the role of endothelial nitric oxide in the relaxant response to green tea (-)epicatechin and its modulation of endothelium-mediated relaxation in the isolated rat mesenteric artery rings.METHODS: Changes in the isometric tension were measured with Grass force-displacement transducers. RESULTS:The (-)epicatechin-induced relaxation was largely dependent on the presence of intact endothelium and was reversed by NG-nitro-L-arginine methyl ester 10 μmol/L or methylene blue 10 μmol/L, the inhibitors of nitric oxidemediated relaxation. L-Arginine at 1 mmol/L antagonized the effect of L-NAME or methylene blue. Pretreatment of endothelium-intact rings with (-)epicatechin 10 μmol/L enhanced the relaxation induced by endothelium-dependent vasodilator, acetylcholine, while this concentration did not influence the endothelium-independent relaxation induced by sodium nitroprusside in the endothelium-denuded artery rings. CONCLUSION: The results indicate that the endothelium-dependent vasodilation by (-)epicatechin is mainly mediated through nitric oxide and low concentration of (-)epicatechin augments endothelium-dependent vasorelaxation in the rat mesenteric arteries.