Abstract
Summary
Administration of 1 μg estradiol benzoate plus 3 mg progesterone into ovariectomized rats for 20 days produced mammary gland DNA levels comparable to those observed in rats on 19th day of pregnancy, while continued injection for periods of 30, 40 and 50 days did not significantly increase observed growth. However, no involutionary changes were noted with long-term injection, indicating a maintainence of the lobule-alveolar system. Administration of 10 mg 3-methylcholanthrene twice weekly for 7 weeks reduced mammary gland growth by approximately 25% in ovariectomized rats given 1 μg estradiol benzoate plus 3 mg progesterone or twice this amount. These hormones prevented development of observable mammary tumors.
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