The binding of 2, 4, 6, 7-estradiol-17 β-3H to its specific cytosol receptor from lactating mammary tissue was studied by the dextran-coated charcoal technique. Nonradioactive estradiol-17β strongly inhibited 2,4,6,7-estradiol-17β-3H binding. Neither 7,12-dimethylbenz(a)anthracene in vivo or in vitro nor dihydrotestosterone in vitro showed significant competition for the estrogen binding sites. Thus the mechanism of action of 7.12-dimethylbenz(a)anthracene in tumorigenesis, or that of dihydrotestosterone in the inhibition of tumor development, does not involve binding of these compounds to the estrogen receptor. These compounds do not inhibit the binding of estradiol-17β to its receptor.
This work was supported by Grant A4670 from the National Research Council of Canada.