Relaxant effects of danshen aqueous extract and its constituent danshensu on rat coronary artery are mediated by inhibition of calcium channels
Introduction
Danshen is the dried root of Salvia miltiorrhiza that belongs to the family of Labiatae. It is a traditional Chinese medicine commonly used for the treatment of cardiovascular diseases such as angina pectoris, myocardial infarction and stroke (Ji et al., 2000). The cardio-protective efficacy of danshen has been studied in ischaemia–reperfusion experiments in animals (Fung et al., 1993, Ji et al., 2000, Kuang et al., 1996, Wu et al., 1993, Zhou and Ruigrok, 1990). The mechanism may involve the ability of danshen to enhance antioxidant defense enzyme activities to decrease or abolish the production of free radicals (Ji et al., 2003). Danshen has also been shown to attenuate the increase in intracellular calcium induced by anoxia–reoxygenation in isolated ventricular myocytes, which would decrease the transformation of xanthine oxidase from xanthine dehydrogenase to reduce the production of oxygen-free radicals (Cao et al., 2003). In addition, danshen lowered the viscosity of whole blood, accelerated electrophoresis of red blood cells, and improved peripheral circulation (Chen, 1981). The vasodilator and hypotensive actions of danshen probably contributed to these effects (Kamata et al., 1993, Lei and Chiou, 1986b, Li et al., 1990).
The content of danshen can be separated into lipid-soluble and water-soluble fractions. Its lipid-soluble fraction contains more than 30 diterpenoid tanshinones; the major active constituents include tanshinone I, IIA, B, cryptotanshinone, dihydrotanshinone I, methylenetanshinone, and isotanshinone IIA (Chang et al., 1990). The putative active components of its aqueous extract are danshensu, salvianolic acid B, lithospermic acids, protocatechuic acid, and rosemarinic acid (Kohda et al., 1989, Liu et al., 1992, Kamata et al., 1993, Chan et al., 2004). However, since the water decoction is the commonly used preparation/method in preparing Chinese folk medicine for human consumption, current interest in studying traditional Chinese medicine is on the aqueous fraction and ingredients.
In animal studies, danshensu has been shown to possess many of the actions of the danshen herb. Hence, it was reported to dilate coronary arteries (Dong and Jiang, 1982), inhibit platelet aggregation (Li et al., 1983), improve microcirculation (Cheng et al., 1987), and protect the myocardium from reperfusion injury of the ischaemic heart (Tang et al., 1989). The mechanism for some of its observe activity may be related to inhibition of Ca2+ aggregation in cardiac cells and prevention of Ca2+ overload (Cao et al., 2003). In addition, danshensu has been found to be able to scavenge oxygen-free radicals (Su et al., 1992, Zhao et al., 1996), inhibit myocardial cell apoptosis (Liu et al., 2001), and protect the endothelial cells against homocysteinemia (Chan et al., 2004). In the present study, we have extracted the aqueous fraction from a danshen herb and quantified contents of danshensu in this extract and in the crude danshen herb. We have also compared the actions of danshen aqueous extract and danshensu on coronary arteries isolated from rats.
Section snippets
Materials and methods
Experiments were performed on male Sprague–Dawley rats (250–300 g) bred and kept by the Laboratory Animal Services Centre of the Chinese University of Hong Kong. All experiments were performed under licence from the Government of the Hong Kong SAR and endorsed by the Animal Experimentation Ethics Committee of the Chinese University of Hong Kong.
Effects on 5-HT-precontracted tone
The precontracted tone produced by 1 μM 5-HT was 0.32 ± 0.05 g, which was sustained over the course of the experiment. Cumulative dosing of danshen aqueous extract and danshensu produced a concentration-dependent relaxation of the 5-HT-precontracted tone with IC50 values of 930.3 ± 133.5 μg/ml and 71.5 ± 11.0 μg/ml (P < 0.001, Fig. 1). Removal of the endothelium did not significantly affect their vasodilator potencies; IC50 values were 842.1 ± 123.8 μg/ml and 84.8 ± 8.8 μg/ml. On the other hand,
Discussion
The present study has demonstrated that the water-soluble fraction of danshen dried herb and one of its constituents, danshensu, have dilatory action on rat coronary arteries. Their vasorelaxant action was 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. The present findings do not support involvement of endothelium-dependent mechanisms in their action.
Previously, we have demonstrated a biphasic
Acknowledgements
The authors thank Ms. Ethel Ng for her technical assistance. Provision of financial support for the present study by The Chinese University of Hong Kong is acknowledged.
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