Endothelium-independent vasodilatory effect of sailuotong (SLT) on rat isolated tail artery

Abstract

Background. Sailuotong (SLT) is a standardized three-herb formulation consisting of extracts ofPanax ginseng,Ginkgo biloba, andCrocus sativusfor the treatment of vascular dementia (VaD). Although SLT has been shown to increase cerebral blood flow, the direct effects of SLT on vascular reactivity have not been explored. This study aims to examine the vasodilatory effects of SLT and the underlying mechanisms in rat isolated tail artery.Methods. Male (250-300 g) Wistar Kyoto (WKY) rat tail artery was isolated for isometric tension measurement. The effects of SLT on the influx of calcium through the cell membrane calcium channels were determined in Ca2+-free solution experiments.Results. SLT (0.1-5,000 mu g/ml) caused a concentration-dependent relaxation in rat isolated tail artery precontracted by phenylephrine. In the contraction experiments, SLT (500, 1,000, and 5,000 mu g/mL) significantly inhibited phenylephrine (0.001 to 10 mu M)- and KCl (10-80 mM)-induced contraction, in a concentration-dependent manner. In Ca2+-free solution, SLT (500, 1,000, and 5,000 mu g/mL) markedly suppressed Ca2+-induced (0.001-3 mM) vasoconstriction in a concentration-dependent manner in both phenylephrine (10 mu M) or KCl (80 mM) stimulated tail arteries. L-type calcium channel blocker nifedipine (10 mu M) inhibited PE-induced contraction. Furthermore, SLT significantly reduced phenylephrine-induced transient vasoconstriction in the rat isolated tail artery.Conclusion. SLT induces relaxation of rat isolated tail artery through endothelium-independent mechanisms. The SLT-induced vasodilatation appeared to be jointly meditated by blockages of extracellular Ca(2+)influxviareceptor-gated and voltage-gated Ca(2+)channels and inhibition of the release of Ca(2+)from the sarcoplasmic reticulum.