OBJECTIVE Danshen and Gegen are traditional Chinese medicines commonly used for the treatment of cardiovascular diseases.In this study, we have identified the major constituents of a Danshen and Gegen formulation (DG; ratio 7∶3) and investigated their actions on rat-isolated cerebral basilar artery.METHODS Rat basilar artery rings were precontracted with 100 nmol·L-1 U46619.Involvement of endothelium-dependent mechanisms was investigated by mechanical removal of the endothelium.Adenylyl cyelase, guanylyl cyclase, and potassium channel involvement were examined by pretreatment of the artery rings with their respective inhibitors.Calcium channel involvement was tested in artery rings incubated with Ca2+-free buffer and primed with U46619 prior to adding CaCl2 to elicit contraction.The constituents of a DG water extract were identified by HPLC.RESULTS Salvianolic acid B, danshensu, puerarin, daidzein and daidzin were identified in the DG water extract.All these agents produced concentration-dependent relaxation of the artery rings that were unaffected by adenylyl cyclase inhibitor, guanylyl cyclase inhibitor, or by endothelium removal, except the latter reduced the maximum response to puerarin by 28%.Moreover, puerarin had no influence on CaCl2-induced vasoconstriction but all the other agents produced concentration-dependent inhibition.Pretreatment with a combination of K + channel inhibitors produced significant inhibition on the vasodilator actions to all these agents, but not on danshensu.CONCLUSION The vasorelaxant actions of salvianolic acid B, daidzein and daidzin involved opening of K + channels and inhibition of Ca2 + influx in the vascular smooth muscle cells.Danshensu produced vasorelaxation solely by inhibition of Ca2+ influx in the vascular smooth muscle cells.In contrast, puerarin produced vasodilatation via an endothelium-dependent mechanism and an endothelium-independent pathway mediated by the opening of K + channels.In spite of differences in their mechanisms of actions, the common cerebrovasodilator activities of these DG constituents suggest they could be beneficial in treatment of obstructive cerebrovascular diseases.