OBJECTIVE: To investigate the vasorelaxant activities of 50 common traditional herbal prescriptions (THPs) on isolated rat aortic rings.METHODS: An electric extractor was used to extract THPs.Rat aortic rings were precontracted using phenylephrine in organ chambers containing Krebs-Henseleit solution.Decoctions of THPs were added in increasing concentrations (10-1000 μg/mL) to investigate vasorelaxant activities.The vasorelaxant effects of THPs were calculated as percentage of contraction in response to phenylephrine.RESULTS: Several THPs such as Tianwangbuxin Dan,Banxiaxiexin Tang,and Mahuang Tang,significantly relaxed precontracted aortic rings.In contrast,Xiaochaihu Tang,Shensuyin,and Guizhifuling Wan significantly contracted aortic rings.Furthermore,these THPs increasingly relaxed or contracted aortic rings relaxed by amlodipine.CONCLUSION: Our findings suggest that hypertension can be treated using THPs.However some THPs can counteract treatment of hypertension.Further studies should be developed on use of THPs for treatment of hypertension are critical,and guidelines for use of traditional herbal medicines to treat hypertension.