Objective To provide experimental evidence for the antihypertensive activity of the flavonoids in flower buds of Coreopsis tinctoria(CT-F)and to investigate the underlying mechanism.Methods The spontaneously hypertensive rats(SHRs)were divided into model,captopril(positive control),and CT-F groups,and the Wistar-Kyoto rats were set as control group,eight in each group.The blood pressure of SHRs,the activity of angiotensin II(Ang-II)in plasma,nitric oxide(NO),malondialdehyde(MDA)and thoracic aorta media thickness in SHRs were measured by tail-cuff method,radioimmunity method,nitrate reductase method,thibabituric acid(TBA)method,and the hematoxylin-eosin staining method.Q-PCR analysis was performed to determine the relative quantity of angiotensin-converting enzyme(ACE),ACEII,angiotensin type 1receptor(AT1R),and TGF-β1 mRNA in left ventricle.Results CT-F could lower the systolic blood pressure of SHRs dramatically(P<0.01).The levels of MDA in serum and Ang II in plasma of SHRs treated with CT-F decreased markedly(P<0.05,0.01),the level of NO in serum increased significantly(P<0.01).In addition,thoracic aorta media thickness in SHRs treated with CT-F was thinner than that of the model group(P<0.05).The mRNA expression of ACE,AT1R,and TGF-β1 in left ventricle was markedly decreased(P<0.05),while that of ACE II was increased(P<0.05).Conclusion CT-F is effective to lower the blood pressure of SHRs,and its antihypertensive effect is probably associated with lowering the oxidative stress by reducing MDA,ameliorating aorta remodeling,dilating vessel by increasing NO and decreasing Ang-II,and regulating the expression of rennin-angiotensin System-related various genes. Objective To provide experimental evidence for the antihypertensive activity of the flavonoids in flower buds of Coreopsis tinctoria (CT-F) and to investigate the underlying mechanism. Methods The spontaneously hypertensive rats (SHRs) were divided into model, captopril (positive control), and CT-F groups, and the Wistar-Kyoto rats were set as control group, eight in each group. The blood pressure of SHRs, the activity of angiotensin II (Ang-II) in plasma, nitric oxide (NO), malondialdehyde ) and thoracic aorta media thickness in SHRs were measured by tail-cuff method, radioimmunity method, nitrate reductase method, thibabituric acid (TBA) method, and the hematoxylin-eosin staining method. Q-PCR analysis was performed to determine the relative quantity of The levels of MDA in angiotensin-converting enzyme (ACE), ACEII, angiotensin type 1 receptor (AT1R), and TGF-β1 mRNA in left ventricle. Results CT-F could lower the systolic blood pressure of SHRs dramatically serum and Ang II in plasma of SHRs treated w The level of NO in serum increased significantly (P <0.01). Addition, thoracic aorta media thickness in SHRs treated with CT-F was thinner than that of the model group (P <0.05) .The mRNA expression of ACE, AT1R, and TGF-β1 in left ventricle was markedly decreased (P <0.05), while that of ACE II was increased lower the blood pressure of SHRs, and its antihypertensive effect is probably associated with lowering the oxidative stress by reducing MDA, ameliorating aorta remodeling, dilating vessel by increasing NO and decreasing Ang-II, and regulating the expression of rennin-angiotensin System-related various genes.