Mechanisms of the dilator action of Danshen (Salvia miltiorrhiza) on rat isolated femoral artery

This study investigates the actions of Danshen crude extract (Salvia miltiorrhiza) on rat isolated femoral artery rings precontracted with phenylephrine. Low concentrations of Danshen (10 to 30 mu g/mL) enhanced the phenylephrine-precontracted tone by a maximum of 31.20 +/- 2.71%. At concentrations 100 mu g/mL or above, Danshen relaxed the precontracted tone, with full relaxation obtained at I mg/mL. Involvement of endothelium-dependant mechanisms in the dilator effect of Danshen was investigated by pretreatment of the artery rings with a cyclooxygenase inhibitor flurbiprofen (10 mu M), a nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME, 100 mu M), a muscarinic receptor antagonist atropine (100 nM), and by mechanical removal of the endothelium; none of these procedures produced a significant change on the Danshen-induced effect. Involvement of endothelium-independent mechanisms was investigated in endothelium-denuded artery rings pretreated with a histamine H-2 receptor antagonist cimetidine (10 mu M), a beta-adrenoceptor antagonist propranolol (100 nM), all adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 mu M), a guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, 10 mu M), and a potassium channel inhibitor tetraethylammonium (TEA, 10 and 100 mM); only TEA was effective in partially inhibiting the Danshen-induced effect. These findings suggest the dilator action of Danshen on rat femoral artery was mediated in part by the opening of TEA-sensitive K+ channels in the smooth muscle cells. Muscarinic receptors, histamine receptors, beta-adrenoceptors, endothelium-derived relaxant factors, adenylyl cyclase, and guanylyl cyclase-dependent pathways did not play a role in its vasodilatory effect.