Relaxant Effects of Matrine on Aortic Smooth Muscles of Guinea Pigs

ObjectiveTo determine whether matrine, a kind of traditional Chinese medicinal alkaloid, can relax the aortic smooth muscles isolated from guinea pigs and to investigate the mechanism of its relaxant effects.MethodsPhenylephrine or potassium chloride concentration-dependent relaxation response of aortic smooth muscles to matrine was studied in the precontracted guinea pigs.ResultsMatrine (1×10−4 mol/L −3.3×10−3 mol/L) relaxed the endothelium-denuded aortic rings pre-contracted sub-maximally with phenylephrine, in a concentration-dependent manner, and its pre-incubation (3.3×10−3 mol/L) produced a significant rightward shift in the phenylephrine dose-response curve, but had no effects on the potassium chloride-induced contraction. The anti-contractile effect of matrine was not reduced by the highly selective ATP-dependent K+ channel blocker glibenclamide (10−5 mol/L), either by the non-selective K+ channel blocker tetraethylammonium (10−3 mol/L), or by the β-antagonist propranolol (10−5 mol/L). In either “normal” or “Ca2+-free” bathing medium, the phenylephrine-induced contraction was attenuated by matrine (3.3×10−3 mol/L), indicating that the vasorelaxation was due to inhibition of intracellular and extracellular Ca2+ mobilization.ConclusionMatrine inhibits phenylephrine-induced contractions by inhibiting activation of α-adrenoceptor and interfering with the release of intracellular Ca2+ and the influx of extracellular Ca2+.