The Rhododendron dauricum L. Flavonoids Exert Vasodilation and Myocardial Preservation.

Rhododendron dauricum L. is an ancient Chinese traditional herb. The pharmacological effects of R. dauricum extract have been shown in chronic tracheitis. The aim of this study was to investigate the cardiovascular effects of Rhododendron dauricum L. flavonoids (RF) on rats and its mechanisms. This study was performed in isolated vascular rings and a rat model of myocardial infarction and isolated myocytes. RF (0.5 - 4 mg/mL) induced a concentration-dependent relaxant effect on the phenylephrine (10(-5) M) and KCl (60 mM) contracted aortic rings, with or without intact endothelium. This effect was attenuated by pretreated with L-NAME (10(-5) M) and K(+) channel inhibitor 4 - AP (1 mM) and TEA (1 mM). The Ca(2+)-induced contraction and PE-induced contraction were obviously attenuated after pretreated with RF (2 mg/mL) for 30 min in Krebs solution, without Ca(2+), containing 10(-4) mol EGTA. KCl (60 mM) significantly increased the intracellular free Ca(2+) concentration ([Ca(2+)]i) and RF inhibited the changes induced by KCl in single cardiac myocytes. RF obviously prolonged the survival time of hypoxia mice pretreated with isoprenaline and reduced the myocardial infarction size in rat coronary artery ligation. These findings suggest that RF induces concentration-dependent vasodilation and myocardial preservation.