Effect of Estrogen on Immobilization Osteoporosis in Rat

The inhibitory effect of estrogens on the development of immobilization osteoporosis in the rat was studied through the analysis of calcium and hydroxyproline content of the femur and tibiae, and the measurement of cortical thickness of the femurs. A marked decrease in the calcium content of the right femur and hydroxyproline content of the right tibiae of rats in which the right hand limb was immobilized through the application of a plaster cast was significantly inhibited by the simultaneous oral administration of 100 μg of conjugated estrogens. Furthermore, administration of conjugated estrogens significantly protected against the decrease in the bone density and the cortical thickness of the femurs of the immobilized limbs of rats. It is concluded that conjugated estrogens diminish the effect ot immobilization in the development of osteoporosis, possibly through the inhibition of bone resorption. (Endocrinology 88: 102, 1971)