Aim Aim To investigate the effect of estrogen on the level of angiotensin Ⅱ(AngⅡ)and the expression of angiotensinⅡ type 1 receptor(AT1R)mRNA in Sprague-Dawley(SD)Rat.Methods Twelve-week-old SD female rats were randomly allocated into three groups:1)ovariectomy(OVX)group,2)ovariectomy+estrogen(OVX+E2)group,and 3)sham operation(Con)group.Blood pressure and body weight were measured.The levels of AngⅡ and estrogen were determined by radioimmunoassay.Expressions of AT1R mRNA in heart,kidney cortex,aorta vascular smooth muscle cell(VSMC)were detected by RT-PCR.Vascular smooth muscle cells from 8-week-old SD rats were cultured.The effect of on the expression of AT1R mRNA was detected by RT-PCR.Result Weight and blood pressure in three groups were not significantly different before ovariectomy.Three months after ovariectomy,weight and blood in ovariectomized rats were significantly higher than that in sham operation animals.Plasma AngⅡ was highly increased and serum estrogen significantly lower in ovariectomized rats.No differences could be observed between the OVX+E2 and the Con group with regard to the serum estrogen.So were plasma AngⅡ levels.The expression of AT1R mRNA in OVX group rats' heart,kidney,aorta was significantly lower.The expressions of AT1R mRNA were inhibited by estradiol in depended-concentration manner in VSMC.Estradiol(10-6 mol/L)remarkably inhibited the expression of AT1R mRNA in VSMC.Conclusion 1.Estrogen could inhibit the expression of AT1R mRNA and reduced plasma AngⅡ level.2.The effect of Estrogen on cardiovascular system may be rely on reducing AngⅡ and AT1R level.