Objective : To investigate the vascular effects of extracts from leaves of Apocynum venetum (ELA) and its mechanisms. Method : Phenylephrine(PE) was used to contract isolated rat thoracic aorta. Concentration relaxation curve of ELA (1× 10-6-3×10-3 g·mL-1) was constructed in cumulative doses manner. Moreover

vasodilator effects of ELA were re-determined after pre-incubated with several antagonists. Result : ELA showed significant vasodilator properties. At low concentration

vascular effects of ELA were inhibited by hemoglobin

methylene blue(MB)

NG-nitro-L-arginine methyl ester (L-NAME) and S-methylisothiourea sulfata (SMT). At high concentration

Ca2+-induced contraction was suppressed by ELA. In addition

the K+ channel blocking agents tetraethylammonium (TEA)

4-aminopyridine (4-AP) and glibenclamide (GLB) inhibited the vasodilator responses of ELA. Conclusion : ELA showed vasodilator effects with property of endothelium-dependency at low concentration and endothelium-independency at high concentration. At low concentration

the vasodilator response of ELA was related to the release of NO

but at high concentration

this action may be associated with Ca2+ and K+.