Covalent binding of ethinylestradiol and estrone to rat liver DNA in vivo.

The covalent binding of [6,7-3H] ethinylestradiol (EE) and [6,7-3H] estrone (E) to liver DNA of 200 g female rats was measured 8 h after the administration of 80 microgram (9.2 mCi) estrogen by gavage. The binding is 1.5 for EE and 1.1 for E, expressed as binding to DNA/dose, in units of mumol hormone/mol DNA phosphate/mmole hormone/kg body wt. It is the same order of magnitude as for benzene and about 10 000 times below the binding of typical liver carcinogens, such as aflatoxin B1 or N,N-dimethylnitrosamine.