Relaxation effect of Polygonum viviparum L. (PV) in isolated rat thoracic aorta. The aorta was removed from a rat, and fat and tissue were carefully dissected away in normal 37°C Krebs solution. Phenylephrine (PE) at 3 μM induced a transient phasic contraction followed by tonic contraction, which lasted at least 10 min in intact or endothelial-denuded aorta. Acetylcholine (ACh) at 10 μM induced relaxation in intact (A, upper trace) but not denuded (A, lower trace) aorta. PV at 100 μg/ml relaxed PE-precontracted intact (B, upper trace) but not denuded (B, lower trace) aorta. (C) Concentration-response curve of vasorelaxation caused by PV on PE-precontracted rat intact aorta. Data are expressed as the mean ± standard error of the mean (S.E.M.) (n ≥ 5 animals per time point).