In this study, we have investigated the actions of cryptotanshinone, an active, lipophilic component of the medicinal herb danshen (Salvia miltiorrhiza), on rat isolated coronary artery rings precontracted with 1 microM 5-hydroxytryptamine (5-HT) and its action compared to the ethanol-extractable fraction of the herb. Extraction of the ethanol-soluble fraction from danshen provided a yield of 1%. The amount of cryptotanshinone determined in this ethanol extract was 3.682%, and it was 6 times more potent than the extract in relaxing 5-HT-precontracted coronary artery rings; IC(50) values were 2.65+/-0.15 microg/ml and 15.82+/-1.07 microg/ml, respectively. Involvement of endothelium-dependant mechanisms in their dilator effects were investigated by pretreatment of the artery rings with a cyclooxygenase inhibitor flurbiprofen (10 microM), a nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM), a muscarinic receptor antagonist atropine (100 nM), and by mechanical removal of the endothelium; none of these procedures produced a significant change on their dilator actions. Involvement of endothelium-independent mechanisms was investigated in endothelium-denuded artery rings pretreated with a beta-adrenoceptor antagonist propranolol (100 nM), an adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 microM), a guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), and a potassium channel inhibitor tetraethylammonium (TEA, 100 mM); these also produced no change on their dilator actions. The possible involvement of Ca(2+) channels was investigated in artery rings incubated with Ca(2+)-free buffer and primed with 1 microM 5-HT for 5 min prior to adding CaCl(2) to elicit contraction. The danshen ethanol extract (100 microg/ml) abolished the CaCl(2)-induced vasoconstriction, whereas, cryptotanshinone (30 microg/ml) produced 59% inhibition. These findings suggest their vasorelaxant effects are independent of pathways mediated by the endothelium, muscarinic receptors, beta-adrenoceptors, adenylyl cyclase, and guanylyl cyclase, whereas, inhibition of Ca(2+) influx in the vascular smooth muscle cells is important for their vasodilator actions. The high vasodilator potency and the quantity of salvianolic acid B contained in danshen ethanolic extract suggest it is an important constituent in this medicinal herb.