Aim:To investigate the vasoactivity of calycosin,a major active component ofAstragali Radix.Methods:Experiments were performed on isolated rat thoracicaortic rings pre-contracted with phenylephrine(PHE)or KCl.Results:Calycosinproduced a concentration-dependent relaxation on the tissue pre-contractedusing PHE with 4.46±0.13 of pD_2 and 95.85%±2.67% of E_(max);or using KCl with4.27±0.05 of pD_2 and 99.06%±2.15% of E_(max),and displaced downwards the con-centration-response curves of aortic rings to PHE or KCl.The relaxant effect ofcalycosin on denuded endothelium aortic rings was the same as on intact endot-helium aortic rings,and its vasorelaxant effect was not influenced by L-NAME orindomethacin.In Ca~(2+)-free solution,calycosin(30 μmol/L)did not have an effecton PHE (1×10~(-6) mol/L)-induced aortic ring contraction.The effects of calycosinand nifedipine where somewhat different;calycosin decreased aortic ring con-tractions induced by the two agonists,but nifedipine displayed a more potentinhibitory effect on KCl-induced contractions than on PHE-induced contractions,and the vascular relaxing effects of calycosin and nifidipine were additive on PHE-induced contraction but not KCl-induced.Conclusion:Calycosin is a vasorelaxant.Its action is endothelium-independent and is unrelated to intracellular Ca~(2+) release.it is a noncompetitive Ca~(2+) channel blocker.The effect of calycosin on Ca~(2+) chan-nel blockade may be different from that of dihydropyridines.This study demon-strated a novel pharmacological activity of calycosin,and supplied a theoreticfoundation for Astragali Radix application. Aim: To investigate the vasoactivity of calycosin, a major active component of Astragali Radix. Methods: Experiments were performed on isolated rat thoracicaortic rings pre-contracted with phenylephrine (PHE) or KCl.Results: Calycosinproduced a concentration-dependent relaxation on the tissue pre- Contractedusing PHE with 4.46±0.13 of pD_2 and 95.85%±2.67% of E_(max);or using KCl with4.27±0.05 of pD_2 and 99.06%±2.15% of E_(max),and directional downwards the con-centration- Response curves of aortic rings to PHE or KCl.The relaxant effect of calycosin on denuded endothelium aortic rings was the same as on intact endot-helium aortic rings,and its vasorelaxant effect was not influenced by L-NAME orindomethacin.In Ca~(2+ )-free solution,calycosin(30 μmol/L)did not have an effecton PHE (1×10~6-6 mol/L)-induced aortic ring contraction.The effects of calycosinand nifedipine where somewhat different;calycosin decreased aortic ring Con-tractions induced by the two agonists,but nifedipine displayed a More potentinhibitory effect on KCl-induced contractions than on PHE-induced contractions, and the vascular relaxing effects of calycosin and nifidipine were additive on PHE-induced contraction but not KCl-induced.Conclusion:Calycosin is a vasorelaxant.Its action is endothelium-independent And is unrelated to intracellular Ca~(2+) release.it is a noncompetitive Ca~(2+) channel blocker.The effect of calycosin on Ca~(2+) chan-nel blockade may be different from that of dihydropyridines.This Study demon-strated a novel pharmacological activity of calycosin, and supplied a theoreticfoundation for Astragali Radix application.