Abstract
Summary
The effects of estrogen, or pro-lactin and STH, on mammary tumor induction by a single feeding of 20 mg of 7, 12-dimethyl-1,2-benzanthracene (DMBA) in ovariectomized Sprague-Dawley rat was investigated. After DMBA administration, mammary tumor incidence in sham-operated controls was 100%. In ovariectomized rats, DMBA failed to induce any mammary tumors by the end of 40 weeks. However, daily treatment with 1 or 10 μg estradiol, for 7 days before and after (total 14 days) DMBA administration, induced mammary tumors in 33 and 23% of rats, respectively. Similar treatment with 1 mg STH and 1 mg prolactin, twice daily for 14 days, elicited mammary tumors in 44% of the rats, while continuous daily treatment with increasing amounts of prolactin and STH for 75 days, resulted in a 66% incidence of mammary tumors. The average number of tumors per tumor-bearing rat was lower and mean tumor latency was longer in the ovariectomized rats given estrogen or STH and prolactin than in sham-operated controls. All tumors were mammary carcinomas. These results indicate that the 2 pituitary hormones, STH and prolactin, can induce mammary carcinogenesis in DMBA-treated rats in the absence of the ovaries. They also suggest that these 2 hormones, as well as estrogen, participate in the initiating and promoting phases of mammary carcinogenesis; and that the effects of estrogen may be partially mediated through stimulation of STH and prolactin secretion by the pituitary.
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