Bamboo leaves, Phyllostachys nigra (LODD. ex. lind-1 MUNRO. L), have been used as a Chinese medicament for thousands of years. Theses leaves have anti-free radical activity and are comparable with the leaf of Ginkgo bilabo, which is one potential resource for natural antioxidant and free radical scavenger. 1) Our previous investigation revealed that bamboo leaves have significant effects on protecting myocardial ischemia in rat, restraining blood platelet aggregation of rabbit, increasing coronal flow and have a vasorelaxant effect on rabbit thoracic aortic rings, and also reduce arterial blood pressure. Here, we further investigated the vasorelaxant effect of four flavonoid C-glycosyl compounds ( Fig. 1): Orientin (Luteolin-8-C-glucoside), Isoorientin (Luteolin-6-Cglucoside), Isovitexin (Apigenin-6-C-glucoside), and Vitexin (Apigenin-8-C-glucoside), first isolated from bamboo leaves, all of which are also found in numerous plants. 2,3) It is reported that these flavonoids possess anxiolytic properties 4,5) and that Orientin possesses antioxidative activity, 6) however, there is no information about the vasorelaxant effect of these compounds. In the present investigation, we examined the vasodilatation effects of these flavonoid C-glycosyl compounds and found only Orientin produced a vasorelaxant effect on rabbit aortic rings. The data from the present study suggested that Orientin relaxed thoracic aortic rings by the nitric oxide-guanosine 3,5-cyclic monophosphate (cGMP) pathway, and in the vascular smooth muscle inhibited the contraction induced by the activation of receptor-operating and voltage-dependent Ca 2ϩ channels. Cyclooxygenase pathway, potassium channels, b-receptors and adenosine-3Ј,5Ј-cyclic phosphoric acid (cAMP) pathway, on the other hand, had no apparent roles. The inhibition of both intracellular Ca 2ϩ release and extracellular Ca 2ϩ influx may be one of the main vasorelaxant mechanisms of Orientin.
MATERIALS AND METHODS
Animal