Effect of estrogen replacement therapy on arthritis and bone mineral density in estrogen-replete rats with collagen-induced arthritis.

The influence of estrogen therapy on changes in arthritis and bone mineral density (BMD) was evaluated using an estrogen-replete collagen-induced arthritis (CIA) rat model. Seven-month-old female Sprague-Dawley rats (n = 30) were divided into the three groups; control (CONT), collagen sensitization (CIA), and CIA + 17beta-estradiol administration for 7 weeks (CIA + E). BMD was measured by peripheral quantitative computed tomography in the proximal tibia every 2 weeks. Eight weeks after the initial sensitization the rats were killed and histomorphometry of tibia was performed. The hind paw thickness increased with time in CIA rats and there was a significant difference between CONT and CIA at 8 weeks after the initial sensitization. Estrogen tended to make the development of arthritis milder. In CIA, BMD at metaphyseal cancellous bone began to decrease with the onset of arthritis and became significantly lower than in CONT after 8 weeks. Compared with the CIA, the deterioration in BMD was inhibited in CIA + E. Histomorphometrical parameters of bone resorption were increased in CIA compared with CONT, and those elevations were reduced by estrogen treatment, but estrogen had no effect on bone formation parameters. In conclusion, estrogen could partially suppress arthritis and bone loss in estrogen-replete rats as well as estrogen-deplete ones.