Effect of estrogen replacement therapy in an early phase on atherosclerosis in ovariectomized rabbits.

Objective To study the effect of estrogen replacement therapy(ERT) in an early phase on atherosclerosis in ovariectomized rabbits.Methods Thirty-six female New Zealand White rabbits were randomly divided into 3 groups: the sham-operation group(group A),the control group(group B),and the estrogen group(group C).Twelve rabbits were ovariectomized and treated with Estradiol Valerate 2?mg/week in the estrogen group,and twelve rabbits were ovariectomized and treated with a placebo in the control group.All rabbits were given a hypercholesterolemic diet(1.5% cholesterol) after the operations for12 weeks.Blood was collected from the femoral artery for plasma lipid analysis,and the aorta were prepared for morphologic and immunohistochemcial analysis.The aortic root(5?mm) was cut and prepared for paraffin sections.The intima/media(I/M) ratio was observed by HE,and contents of collage fiber were observed using picric acid-sirius red staining techniques,positive percentage of macrophage cells was measured using immunohistochemistry in cross sections.The ratio of atherosclerotic plaque area/aortic wall surface in the rest of the aorta was measured using oil red staining in longitudinal sections.Results Either the Intima/media ratioor the ratio of atherosclerotic plaque area/aortic wall surface in groups A and C was significantly less than in group B(P0.01),and the positive percentage of macrophage cells in groups A and C was also significantly less than in group B(P0.01),but there were more collage fibers in the atherosclerotic plaque in group C than in groups A and B(P0.05).Conclusion Early estrogen replacement therapy can improve blood lipid metabolism and reduce the number of macrophages in the plaque,and increases plaque collagen fiber contents,plaque stability,and inhibits atherosclerosis progression in ovariectomized rabbits.