Aqueous extract of Schizandra chinensis fruit causes endothelium-dependent and -independent relaxation of isolated rat thoracic aorta

An aqueous extract of Schizandra chinensis fruit (ScEx) has long been used to promote the vascular health of postmenopausal women in Korea. This study investigated the ability of ScEx to relax rat aorta constricted with norepinephrine (NE) and the mechanism(s) of such relaxation. ScEx induced partial, endothelium-dependent relaxation. In particular, the relaxation induced by lower concentrations of ScEx (0.1 and 0.3 mg/ml) was largely endothelium-dependent, and was essentially abolished by NG-nitro-l-arginine, methylene blue, 1H-[1,2,3] oxadiazole [4,4-a] quinoxalin-1-one, indomethacin, or ICI 182,780. The results indicate that the response to ScEx involves enhancement of the nitric oxide (NO)-cGMP system, and that it occurs via estrogen receptors. The magnitude of the inhibition with these treatments decreased with increasing ScEx concentration, however, indicating that other vasorelaxation mechanisms are involved, which depend on the ScEx concentration. Calcium concentration-dependent contraction curves in high potassium depolarization medium were shifted significantly to the right and downward after incubation with ScEx (0.3 and 1.0 mg/ml), implying that ScEx is also involved in inhibition of the extracellular calcium influx to vascular smooth muscle. These data demonstrate that ScEx caused both endothelium-dependent and -independent vasorelaxation, which may contribute to understanding the cardiovascular protective effect of ScEx.