[The effects of early intermittent high-dose estrogen treatment on bone structure of ovariectomized rats].

OBJECTIVES: The effects of various estrogen replacement protocols to prevent bone loss following ovariectomy have been the subject of many studies in rats. This study was designed to determine the effects of early intermittent high-dose estrogen replacement therapy, which has hitherto not been studied, on bone structure of ovariectomized rats. METHODS: Bilateral ovariectomies were performed in 20 female mature non-pregnant Wistar rats. All the animals were randomly assigned to two groups to receive either subcutaneous 17 beta-estradiol (25 mg/kg) or only sesame oil on days 15 and 22 after ovariectomy. Fourteen days after the last injection, the rats were sacrificed and proximal femurs were removed for both light and electron microscopic analyses. RESULTS: In the light microscopic analysis, control femurs exhibited a marked destruction in the structure of the cancellous bone, whereas estradiol-treated rats had almost normal cancellous bone. Ultrastructural analysis showed degeneration and increased turnover in bone cells of the control femurs, whereas the bone cells and the bone matrix appeared almost normal in the treatment group. A statistically significant increase in serum estrogen levels was found in estradiol-treated rats (580+/-124 pg/ml versus 62+/-16 pg/ml, p<0.001). CONCLUSION: Intermittent high-dose estrogen treatment prevents cancellous bone loss in the proximal femurs of ovariectomized rats through inhibition of bone turnover and results in significantly increased serum estrogen levels.