Direct vasorelaxation and vasoprotective properties of total flavonoids of Flos Chrysanthemi and its main bioactive components in rat resistance artery

The present study was designed (i) to test the hypothesis that the endothelium‐derived hyperpolarizing factor (EDHF) and nitric oxide (NO)‐induced vasorelaxation are impaired following exposure to superoxide anion, and (ii) to further investigate the vasoprotection of total flavonoids of Flos Chrysanthemi (TFFC), and its main bioactive components, luteolin and apigenin, on impaired vasodilation. The third branch of the rat superior mesenteric artery was isolated for in vitro isometric tension experiments. TFFC, luteolin and apigenin, evoked sustained relaxation. The EDHF and NO components of ACh‐induced endothelium‐dependent and ‐independent relaxation were assessed with and without 15 min exposure to superoxide anion from pyrogallol. Vasorelaxation, which was induced by EDHF or NO, but not sodium nitroprusside or pinacidil, was significantly impaired by exposure to superoxide anion. By concurrent exposure to TFFC, the effect of superoxide anion was attenuated. Specifically, luteolin and apigenin both induced vasoprotection against loss of the EDHF and NO‐induced relaxation. The results of this study suggest that superoxide anion impairs ACh‐induced relaxation through the impairment of both EDHF‐ and NO‐mediated relaxation. TFFC, luteolin and apigenin protect arteries from injury by superoxide anion, suggesting that they may have anti‐oxidant effects in cardiovascular diseases.