Induction of Vasorelaxation in Isolated Rabbit Aorta by Epimedium Brevicornum Maxim Leaf Extracts

The vasorelaxant effect of Epimedium brevicornum Maxim (Berberidaceae) (EB) was studied in isolated rabbit thoracic aorta. Results showed that water extract of EB (EB-W) concentration-dependently antagonized phenylephrine (PE)-induced vasoconstriction at the concentrations ranging from 0.001 to 1 mg/mL with an EC50 of 12.4 ± 1.5 μg/mL. EB-W evoked vasorelaxation was significantly, however, not completely inhibited by endothelium removal, NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) and 1-H-[1,2,4] oxadiazolo [4, 3-α] quinoxalin-1-one (a guanylate cyclase inhibitor) pretreatment, indicated that this vasorelaxant effect to be mediated partially through endothelium-dependent mechanism. The residue relaxation caused by EB-W in PE-precontracted endothelium-denuded preparations was abolished in the presence of high extracellular K+ concentration (60 mM) and by an ATPsensitive K+ channel blocker glibenclamide pretreatment. Taken together, these results suggested that E. brevicornum may relax vascular beds via both direct NO releasing effect from endothelium and activation of an ATPsensitive K+ channel on smooth muscle.