Introduction: Diabetes mellitus and obesity are associated with cardiovascular morbidity and mortality in part due to vascular abnormalities such as endothelial dysfunction. Previous studies have demonstrated that partitions in ethyl acetate (MMAc) and dichloromethane (MMDic) of the hydroalcoholic extract of Mandevilla moricandiana leaves had vasodilator and antioxidant activities. The aim of this work was to investigate the mechanism of action of MMAc and MMDic and it’s effects on the vascular aortic reactivity from obese and diabetic rats, besides evaluating the chemical profile of the partitions. Materials and methods: In the obesity model, male Wistar rats received subcutaneous injections of monosodium glutamate (MSG, 4g/kg body weight) during the first 5 days of life and protocols were performed at 150 days of age. In the diabetes model, male Wistar rats (140-180g) received a single injection of streptozotocin (DM-1, 60 mg/kg body weight) and the protocols were carried out after 12 weeks. The mechanism of vasodilator action was performed by pre-treatment of the aortic rings with the L-NAME, ODQ, fulvestrant and diphenhydramine blockers, eNOS, soluble guanylate cyclase, histamine H1 receptors and estrogen ERα receptors inhibitors, respectively. Vascular reactivity was evaluated in aortic rings prepared for isometric tension recording. Concentration-response curves to phenylephrine and acetylcholine (10-9 - 10-5 M) were obtained in the absence and presence of 3 μg/mL of MMAc or MMDic partitions. Partitions were purified by chromatographic techniques and identified by HPLC-MS-MS, GC-MS, and 1H-NMR and 13C-NMR. The local Animal Care and Use Committee approved all protocols (License MAC019). Results: Pretreatment of aortic rings with endothelium using L-NAME and ODQ produced a complete inhibition of the vascular relaxation induced by MMAc and MMDic, indicating the involvement of the NO/cGMP pathway to the effect. In an attempt to determine the receptor involved in the activation of the NO/cGMP system, aortic rings were incubated with fulventrant and diphenydramine. In the presence of 10 μM diphenhydramine, MMAc and MMDic-induced relaxation at 30 μg/mL ware reduced from 85.05% ± 3.64% to 41.47% ± 7.22% and from 93.81% ± 1.68% to 24.25% ± 5.77%, respectively (p <0.05; n=6). In addition, fulvestrant induced a rightward displacement of the concentration-response curve of MMAc, but without a reduction of the maximal relaxation. However, the MMDic -induced relaxation at 30 μg/mL was reduced to 58.40% ± 11.34% (p<0.05; n=6). In aorta of MSG animals, the maximum relaxation of acetylcholine increased from 31.60% ± 1.85% to 63.34% ± 5.36% (p<0.05) in the presence of MMAc and 40.04% ± 4.50% to 64.97% ± 3.44% (p<0.05) in the presence of MMDic. However, both partitions had no effect on vascular reactivity in the aorta of diabetic rats. About the chemicals profiles, chromatographic fractionation of MMAc generated 8 fractions, of which 6 presented vasodilator activity. The substances identified in the active fractions were: procyanidin trimer type A {(m/z: 863 [M-H]- and MS2: 711, 573 and 289); kaempferol {(m/z: 285 [M-H]-}; quercetin {(m/z: 301 [M-H]-} and a mixture of ursolic acid and oleanolic acid {(m/z: 455 [M-H]-}. These propositions were confirmed by NMR of 1H and 13C 1D and 2D and compared with literature data. Chromatographic fractionation of MMDic generated 10 fractions, of which only 1 presented vasodilator activity, and a presence of ursolic acid, oleanolic acid and betulin was suggested by GC-MS. Conclusion: Our results demonstrated that MMAc and MMDic-induced vascular relaxation in the rat aorta is mediated by the NO/cGMP signaling pathway, at least partially, through the activation of histamine H1 receptors and estrogen Erα receptors. Both partitions improved vascular dysfunction only in the obesity model. The vasodilatory activity presented for MMAc can be attributed to the presence of quercetin, kaempferol, procyanidin trimer type A, ursolic acid and oleanolic acid. While the presence of ursolic acid, oleanolic acid and betulin, can be responsible for the effect of MMDic, indicating that it could be considered a source of natural bioactive products with vasodilatory activity.