Salvianolic acid B, an aqueous component of danshen ( Salvia miltiorrhiza), relaxes rat coronary artery by inhibition of calcium channels

Abstract

In this study, we have investigated the mechanism of action through which salvianolic acid, a constituent of the medicinal herb danshen ( Salvia miltiorrhiza), causes relaxation of isolated coronary artery rings precontracted with 1 μM 5-hydroxytryptamine (5-HT). The vasorelaxant effects of salvianolic acid B were also compared with the aqueous extract of danshen. Extraction of the water-soluble fraction from danshen provided a yield of 17.5%. The amount of salvianolic acid B determined in this aqueous extract was 3.9%, and the extract was 6.3 times less potent than salvianolic acid B in relaxing 5-HT-precontracted coronary artery rings; IC 50 values were 930.3 ± 133.5 μg/ml and 147.9 ± 17.4 μg/ml, respectively. Removal of the endothelium did not significantly affect their vasodilator potencies; IC 50 values were 842.1 ± 123.8 μg/ml and 160.3 ± 25.9 μg/ml. On the other hand, a potassium channel inhibitor tetraethylammonium (TEA, 10 mM) shifted their concentration-response curves by 1.7 and 2.9 folds. The possible involvement of Ca 2+ channels was investigated in artery rings incubated with Ca 2+-free buffer and primed with 1 μM 5-HT or 60 mM KCl for 5 min prior to adding CaCl 2 to elicit contraction. In 5-HT-primed preparations, 2 mg/ml danshen aqueous extract and 0.72 mg/ml salvianolic acid B abolished the CaCl 2-induced vasoconstriction, whereas, in KCl-primed preparations, 10 mg/ml danshen aqueous extract and 1.44 mg/ml salvianolic acid B produced 90% inhibition. These findings suggest the vasorelaxant effects of danshen aqueous extract and salvianolic acid B were produced by inhibition of Ca 2+ influx in the vascular smooth muscle cells. The opening of K + channels had a minor contribution to their effects, but endothelium-dependent mechanisms were not involved. The high vasodilator potency and the quantity of salvianolic acid B contained in danshen aqueous extract suggest it is an important vasodilator constituent in this medicinal herb.