Tamoxifen prevents bone loss in castrated male mice

The selective estrogen receptor modulator tamoxifen was administered to int act and castrated mate mice, and its effects on tibial bones and circulator y calcium, phosphate and testosterone mire compared with controls and castr ated animals. Tamoxifen in a dose used in humans for treatment of breast ca ncer decreased the weight of seminal vesicles, an organ which is highly sen sitive to the androgenic effect, decreased the concentration of testosteron e, but did not have any negative effect on bone density or mineral content in intact mice. When castrated mice with extraordinarily low concentrations of testosterone and weights of seminal vesicles were treated with tamoxife n, the changes in bone density and bone mineral resulting from castration w ere not only entirely prevented, but increased above the values of intact m ice. At the same time, cortical bone was lost in orchidectomized mice, and this decrease in cortical thickness of femur was completely prevented by ta moxifen treatment. Pharmacological therapy with estrogen agonist on bone, t amoxifen in androgen deficient adult male mice prevents bone loss.