Gomisin a from Schisandra chinensis induces endothelium-dependent and direct relaxation in rat thoracic aorta

Schisandra chinensis (SC), a member of the Magnoliaceae family, has been used to improve the vascular health for postmenopausal women in Korea. In order to provide some scientific ratio-nales for such effectiveness, this study investigated the vascular effects of gomisin A (GA) from SC. In the endothelium (ED)-intact rings of rat thoracic aorta, GA (1 x 10(-6) to 3 x 10(-4)M) caused a concentration-dependent relaxation which was markedly attenuated not only by removal of ED but also by pretreatment with N-G-nitro-L-arginine (10(-4) M) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (3 x 10(-5) M). Direct measurement of nitrite, a metabolite of nitric oxide (NO), confirmed that NO production in isolated aorta was increased by GA. In the ED-denuded specimens, the relaxation by GA was not abolished but reduced significantly. The relaxation by GA in ED-denuded aortic rings were clearly inhibited by calyculin A (3 x 10(-8) M), an inhibitor of MLC phosphatase. Furthermore, the phenylephrine-enhanced phosphorylation ratio of MLC was significantly attenuated by GA. Based on these results, it is suggested that GA induced vascular relaxation by partially activating ED-dependent NO pathway, and partially dephosphorylation of MLC.