The effects of the estrogen receptor blocker, Faslodex (ICI 182,780), on estrogen-accelerated bone maturation in mice.

Sex steroids accelerate bone maturation, but it is believed that estrogen action is needed for terminal epiphyseal fusion. In this study, we investigated the effects of a new estrogen-blocking agent, Faslodex (ICI 182,780), on estrogen-accelerated skeletal maturation in immature mice. On day-of-life 2 through 8, mice pups received either estradiol (5 microg/100 g body weight), Faslodex (100 microg/100 g body weight), a combination of Faslodex + estradiol, or vehicle alone. Skeletal maturation was assessed with a scoring system based on the size and appearance of epiphyseal plates in the forepaw and the lumbar spine. Estradiol caused acceleration of bone maturation in our mouse model (p < 0.05). Faslodex blocked the effect of estrogen, such that the mice receiving Faslodex + estradiol did not vary significantly from controls. Faslodex may prove useful in the treatment of patients with diseases causing rapid skeletal maturation, such as precocious puberty.