['To investigate the effect of Astragalus membranaceus (AM) on endothelial-dependent (EDV) and non- dependent (EIV) vascular relaxation in ex vivo thoracic aortic rings of obese rats.', 'Fifteen SD rats were randomized into 3 equal groups, namely the control group fed with normal chow, obese group with high-fat chow, and AM intervention group fed with high-fat chow and daily AM gavage. The rats were sacrificed after 6 weeks of feeding, and the aortic rings were dissected and cut into 3-mm rings. The response to acethylcholine (Ach) and sodium nitroprusside (SNP) were examined in organ bath. In ex vivo study, the aortic rings obtained from the control group and obese group were incubated with AM or vehicle for 3 h in organ bath before testing the EDV and EIV. The body weight and weight of the visceral fat in each group were recorded.', 'The weight of visceral fat was greater in the obese group than in the control group, and a 6-week AM treatment significantly reduced the fat tissue due to high-fat diet. The maximum EDV value was (87.0 - or + 3.5)% in the control group, (54.8 - or + 7.8)% in the obese group, and (69.8 - or + 5.7)% in AM intervention group; the EIV values were comparable between the 3 groups. After incubation with AM, the maximum EDV values of aortic rings obtained from the obese group were significantly increased from (55.6 - or + 8.3)% to (85.1 - or + 4.5)%.'] Does [ Astragalus membranaceus improve endothelial-dependent vasodilator function in obese rats ]?