| Summary: | Background and aim: The leaves of Garcinia cowa (G. cowa) are used in Thai traditional medicine to improve blood circulation. However, there is no scientific evidence to confirm this therapeutic claim. Here, we investigated the vasorelaxing effect and its underlying mechanisms of an aqueous extract of G. cowa leaves in rat thoracic aortic rings. Materials and methods: Dried leaves of G. cowa were extracted with water, followed by phytochemical analysis. Vascular reactivity experiments were performed in isolated rat thoracic aortic rings using an organ bath system. The results were recorded using the data acquisition system Power Lab. Results: Phytochemical analysis showed that the leaves of G. cowa are rich in polyphenols and flavonoids, especially kaempferol, vitexin, and isovitexin. The G. cowa leaf extract caused a concentration-dependent relaxation of aortic rings. This effect was attenuated by denudation of the endothelium, or by pre-treatment of the aortic rings with l-NAME, ODQ, indomethacin, or glibenclamide, but not with TEA. Conclusion: This study indicates that G. cowa leaf extract induces vasorelaxation through both endothelium-dependent and endothelium-independent manners. Its mechanism of action mainly involves the production of nitric oxide and prostanoids, as well as opening ATP-sensitive K+ channels. The vasorelaxing effect of G. cowa leaf extract is probable promoted by the action of flavonoids.
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