Induction of endothelium-dependent relaxation in rat aorta via nitric oxide production caused by the aqueous extract of Astragalus membranaceus Bunge leaves

Abstract

This study was designed to investigate the effects and associated mechanisms of the aqueous extract of Astragalus membranaceus Bunge (A. membranaceus) leaves on vascular contractions in rat thoracic aorta. In intact endothelium rings that had been pre-contracted with noradrenaline, the aqueous extract induced relaxation of the rings in a dose-dependent manner. Although this induction process was also effective following pre-incubation of the rings with indomethacin, pre-incubation with N ω-nitro-L-arginine methyl ester inhibited the induction. In an in vivo study, the intravenous injection of the aqueous extract led to an increase in serum nitric oxide levels in rat. To elucidate the effective component with the aqueous extract, the mixture was partitioned between water and n-butanol. The water-soluble fraction induced endothelium-dependent vasodilation, whereas the n-butanol-soluble fraction relaxed rat aortas pre-contracted with noradrenaline, both in the presence and absence of endothelium. These results suggest that endothelium-dependent nitric oxide could play a major role in vasodilation induced by the aqueous extract of the A. membranaceus leaves. Moreover, the active ingredients of the water extract could be included in the water-soluble fraction.