Vasodilatory actions of xanthones isolated from a Tibetan herb,Halenia elliptica |
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Authors: | Yan Wang Jian-Gong Shi Mu-Zou Wang Chun-Tao Che John H.K. Yeung |
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Affiliation: | 1. School of Chinese Medicine, The Chinese University of Hong Kong, Hong Kong, China;2. Institute of Materia Medica, Chinese Academy of Medical Sciences, Beijing 100050, China;3. Department of Pharmacology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China |
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Abstract: | In this study, six major xanthones, isolated and identified from Halenia elliptica were investigated for their vasodilatory actions in isolated rat coronary artery. The xanthones, including 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1), 1-hydroxy-2,3,4,7-tetramethoxy-xanthone (HM-2), 1-hydroxy-2,3,4,5-tetramethoxy-xanthone (HM-3), 1,7-dihydroxy–2,3,4,5-tetramethoxy-xanthone (HM-4), 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5) and 1,7-dihydroxy-2,3-dimethoxy-xanthone (HM-7) caused vasodilation in the coronary artery pre-contracted with 1 μM 5-hydroxytryptamine (5-HT), with EC50 values ranging from 1.4±0.1 μM (HM-1) to 6.6±1.4 μM (HM-2). The EC50 values of the other xanthones were between those of HM-1 and HM-2. Removal of endothelium of the coronary artery led to decreases in the vasorelaxant effects of HM-1, HM-7 but not HM-2, HM-3, HM-4 and HM-5. Our results showed that xanthones isolated from Halenia elliptica are vasoactive substances which exhibit either endothelium-dependent or endothelium-independent mechanisms in rat coronary artery. The potency and mechanism(s) of the vasorelaxant effects of these xanthones may be relevant to the structure–activity differences in the level and the position of the substituent groups with the primary xanthone structure. |
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