Effects of high hoses of estrogen on prolactin-binding activity and growth of carcinogen-induced mammary cancers in rats.

Specific binding sites for prolactin (PRL) were present in membrane preparations from 7,12-dimethylbenz(a)-anthracene-induced rat mammary tumors. The specific binding of PRL was time and temperature dependent. A significant negative correlation was noted between administered doses of estrogen and the subsequent binding of PRL to tumor cell membranes. Injections of 10 or 25 mug estradiol benzoate daily for 10 days effectively inhibited mammary tumor growth and significantly reduced specific PRL binding to mammary tumor cell membranes.