Effects of San'o-shashin-to and the constituent herbal medicines on theophylline-induced increase in arterial blood pressure of rats

San'o-shashin-to, composed of Scutellariae Radix, Coptidis Rhizoma and Rhei Rhizoma (volume ratio= 1 : 1 : 1), reduced an increase in arterial blood p ressure of anesthetized rats induced by theophylline (5 mg/kg, i.v.). The h ypotensive effect of San'o-shashin-to was produced in a dose dependent mann er and was maximum at its 0.5 g/kg. Then the constituent herbal medicines w ere examined for their possible hypotensive effect. Scutellariae Radix of 0 .2 g/kg slightly decreased in the blood presure. Rhei Rhizoma of 0.2 g/kg d ecreased in the blood pressure and the hypotensive effect was significantly produced even at the dose of 0.05 g/kg, while Coptidis Rhizoma had little effect. Among fractions of San'o-shashin-to separated by Diaion HP-20 colum n chromatography, the 50% methanol-eluted fraction had a large hypotensive effect. The 50% methanol-eluted fraction of Scutellariae Radix and Rhei Rhi zoma were also effective and, especially, that of Rhei Rhizoma had a large hypotensive effect. In isometric tension study, Scutellariae Radix and Rhei Rhizoma (10-30 mug/ml) slightly exerted contractile and relaxant effects, respectively, on the phenylephrine-contracted endothelium-intact rat thorac ic aorta. Coptidis Rhizoma (1-10 mug/ml) caused both endothelium-dependent and -independent relaxantion. These results suggest that the hypotensive ef fect of San'o-shashin-to is not mediated by the direct action on blood vess el but by other actions. Some components in Scutellariae Radix and Rhei Rhi zoma, especially in the latter may play a main role in the hypotensive effe ct.