Vasorelaxant Activities of Aqueous Extracts from Twenty Medicinal Plants Used in Oriental Medicines in Isolated Rat Aorta

Water extracts from 20 medicinal plants, traditionally used for postmenopausal symptoms in Korea, were exam-ined for their vasorelaxant activity in isolated rat thoracic aorta rings precontracted with norepinephrine (NE). Among the 20 medicinal plants, Cornus officinalis (CoEx, 0.3 mg/mL), Schisandra chinensis (ScEx, 0.3 mg/mL), Erythrina variegate (EvEx, 0.3 mg/mL), and Epimedium koreanum (EkEx, 0.3 mg/mL) showed rapid relaxation of endothelium-intact aorta (69±4%, 40±3%, 25±2%, and 23±3 % of active tone induced by NE, respectively). In contrast, the extracts of Erythrina variegata (EvEx), Angelica gigas (AgEx), Pueraria thunbergiana (PtEx), and EkEx lead to gradual (i.e., long-term) relaxation to baseline in endothelium-intact vessels. The time to com-plete relaxation was 20～40 min. These 6 plant extracts were selected for the investigation of possible underlying mechanisms. The CoEx-, ScEx-, or EkEx-induced rapid relaxations were virtually abolished by endothelium denu-dation, and were significantly inhibited by pretreatment with nitric oxide (NO) synthase inhibitor NG-nitro-L-argi-nine (L-NNA, 10 μM), indicating that increased formation of NO might contribute to the endothelium-mediated relaxation. In long-term responses, the endothelium denudation did not affect PtEx-induced relaxation, whereas it delayed responses by EvEx and AgEx, and significantly inhibited the effect of EkEx. Among EvEx, AgEx, and PtEx, EvEx attenuated the CaCl2-induced vasoconstriction in high-potassium depolarized medium, implyin