Danazol binding and translocation of steroid receptors.

Danazol, an isoxazol derivative of ethinyl testosterone which suppresses gonadotropin levels and acts as a weak androgen, is shown by competition studies to bind rat androgen receptor (Ki 10(-8M) and progestin receptor (Ki 10(-7)M) but not estrogen receptor. Effective antigonadotropin doses to the rat in vivo translocate only androgen receptor to target cell nuclei; nuclear receptor levels remain elevated more than 6 hours. The same translocation occurs when rat uteri are incubated with danazol in vitro, showing that the action of danazol is direct and probably does not require metabolic conversion of the drug.