DIFFERENTIAL BINDING OF ANTI-ESTROGENS BY RAT UTERINE AND CHICK OVIDUCT CYTOSOL

Analysis of the interactions of two synthetic estrogen antagonists, tamoxifen and CI 628, with rat uterine and chick oviduct cytosol revealed significant differences in the antiestrogen binding properties of these tissues. In the rat uterus CI 628, tamoxifen and estradiol were bound to a similar number of saturable binding sites and estradiol could completely inhibit the binding of tritiated antiestrogens to these sites. In contrast, high affinity, saturable antiestrogen binding sites in chick oviduct were present at three times the concentration of estradiol binding sites and estradiol could only partially inhibit the binding of tritiated antiestrogens to these sites. It is concluded that antiestrogens bind to the estrogen receptor in both tissues and that chick oviduct has an additional saturable antiestrogen binding site distinct from the classical estrogen receptor site. © 1979.