Extracts from Schizandra chinensis fruit activate estrogen receptors: a possible clue to its effects on nitric oxide-mediated vasorelaxation.

Schizandra chinensis fruit has long been used for the treatment of cardiovascular symptoms associated especially with menopausal symptoms in Korea. To provide a scientific rationale for such uses, we have investigated the vasorelaxant effects of Schizandra chinensis fruit on the vasomotor tone of the rat thoracic aorta in an organ bath. The crude extracts of Schizandra chinensis fruit (SC-Ex) elicited a transient relaxing response in the endothelium-intact rat aorta contracted with norepinephrine. This relaxant effect was abolished by removal of the endothelium, and also by pretreatment with nitric oxide synthase inhibitor. We then examined whether this vasodilatory effect occurs through estrogen receptor by reporter assays. SC-Ex activated the estrogen-responsive luciferase gene in COS cells transiently transfected with estrogen receptor and reporter plasmids. The activation was maintained in the butanol-soluble fraction and further increased in the successively fractionated C(18) cartridge-adsorbed fraction (SC-ADF). Reporter gene activation by SC-ADF was inhibited by the specific estrogen receptor antagonist ICI 182,780, indicating that the effect is estrogen receptor dependent. However, SC-ADF failed to activate the androgen receptor in COS cells transfected with the corresponding receptor and reporter plasmids. These data show that extracts of Schizandra chinensis fruit act as a weak phytoestrogen.