Abstract
This study investigated the relaxant actions of danshen (Salvia miltiorrhiza) and its lipid-soluble- and water-soluble-fractions on endothelium-denuded rat isolated femoral artery rings. Danshen, its water-soluble fraction and its lipid-soluble fraction produced relaxation of the phenylephrine-precontracted artery rings with IC50 values of 149 +/- 20 microg/mL, 160 +/- 25 microg/mL, and 23 +/- 6 microg/mL, respectively. Pretreatment of the artery rings with a non-selective potassium channel inhibitor tetraethylammonium (TEA, 10 mM) produced a significant two-fold rightward shift of the concentration-response curve to danshen and a four-fold shift to its water-soluble fraction, but had no effect on the lipid-soluble fraction. A 3.3-fold shift was produced on the concentration-response curve of danshen when the artery rings were pretreated with a mixture of 10 mM TEA, 1 mM 4-aminopyridine (K(V) blocker), 1 microM glibenclamide (K(ATP) blocker), 100 nM iberiotoxin (BK(Ca) blocker), and 100 microM barium chloride (K(IR) blocker). Involvement of Ca2+ channels was investigated in endothelium-denuded artery rings incubated with Ca2+-free buffer and primed with 1 microM phenylephrine or 60 mM KCl for 5 minutes prior to adding CaCl2 to elicit contraction. In artery rings primed with phenylephrine, pretreatment with 1 mg/mL danshen, 1 mg/mL water-soluble fraction of danshen, 0.1 mg/mL lipid-soluble fraction of danshen, and 100 nM nifedipine abrogated the CaCl2-induced contraction. On the other hand, in artery rings primed with KCl, these agents produced 40%, 25%, 53%, and 92% inhibition on the maximum contraction induced by CaCl2, respectively. Increasing the concentrations of danshen and its water-soluble fraction to 3 mg/mL, and the lipid-soluble fraction to 0.3 mg/mL further reduced the maximum contraction to 92%, 93%, and 83%, respectively. Taken together, these findings suggested the vasorelaxant actions of danshen and its fractions were produced primarily by inhibition of Ca2+ influx in the vascular smooth muscle cells and a small component was mediated by the opening of K+ channels.
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