Relaxant effects of total flavonoids of buckwheat flowers and leaves on rat thoracic aorta and underlying mechanisms

Aim To explore the vasodilative effect on rat thoracic aortic ring of total flavonoids of Buckwheat flowers and leaves(TFBFL) and the underlying mechanisms.Methods Isometric tension measurements were used to study the effect of TFBFL on isolated rat thoracic aorta rings.Laser scanning confocal microscope was employed to measure the concentration of intracellular free calciums.Results In aorta rings precontracted with phenylephrine or potassium chloride,TFBFL caused a dose-dependent relaxation in both endothelium-intact and denuded rings and the relaxant effect of TFBFL was more potent on endothelium-intact aorta rings than that on endotheliumdenuded aorta rings(P0.01).The relaxant effect with endothelium was significantly attenuated when the preparation was pretreated with L-NAME(100 mmol·L~-1),a NOS inhibitor.Cumulative application of Ca~2+ induced a concentration-dependent contraction in rat aortic rings without endothelium in Ca~2+ free K-H solution pre-depolarized with KCl;Both Ca~2+-and PE-induced contraction were dramatically attenuated after pretreated with TFBFL(0.8 mg·L~-1)for 10 min in Krebs solution without Ca~2+.TFBFL also dose-dependently decreased the intracellular free calcium concentration measured by laser scanning confocal microscope.Conclusions TFBFL exerts a dose-dependent vasodilative effect on rat isolated aorta rings and the possible underlying mechanism may be involved in the reduction of intracellular Ca~2+ mobilization.TFBFL may also stimulate the release of nitric oxide from endothelium cells which can partly induce the vasodilative effect.