Role of endothelium/nitric oxide in vascular response to flavonoids and epicatechin

AIM: To examine the role of endothelium in the vascular responses to flavon oids, baicalein, baicalin, cardamonin, alpinetin, and to purified jasmine g reen tea (-) epicatechin in the isolated rat mesenteric artery rings. METHO DS: The isometric contraction was measured by Grass force-displacement tran sducers. RESULTS: Both baicalein and baicalin enhanced the phenylephrine-in duced contractile response in the endothelium-intact rings. This enhancemen t was abolished by pretreatment with the nitric oxide inhibitor NG-nitro-L- arginine or in the absence of the endothelium. Both flavonoids also inhibit ed the acetylcholine-induced endothelial nitric oxide-dependent relaxation. In contrast, cardamonin, alpinetin or (-)epicatechin induced both endothel ium-dependent and -independent relaxation. N-G-nitro-L-arginine meyhyl este r or endothelium denudation attenuated the endothelium-dependent relaxation to the same extent. CONCLUSION: Baicalein and baicalin enhanced the phenyl ephrine-induced contraction most likely through inhibiting production or/an d release of endothelial nitric oxide. Whilst, cardamonin-, alpinetin- or ( -)epicatechin-induced endothelium-dependent relaxation is primarily mediate d through endothelial nitric oxide.