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J Natl Cancer Inst. 1974 Jan;52(1):283-4.

Direct action of estradiol on rat mammary tumors.



This study reports a direct action of 17-beta-estradiol on protein synthesis by 7, 12-dimethylbenz (alpha) anthracene (DMBA) induced rat mammary tumors. Sprague-Dawley female rats were given 20 mg of DMBA in sesame oil by gastric tube. Mammary tumors developed. When tumors reached 1.5 to 2 cm in diameter, animals were ovariectomized. At 4-7 days later animals were killed and tumors removed. Microscopic examination confirmed the tumors to be carcinoma of adenoid cystic variety with regressive changes. 14 tumors from 14 animals were found suitable for study. In vitro treatment with 17-beta-estradiol gave rise to a 7% increase in the rate of 3H-leucine incorporation, expressed as dpm/mg of TCA-insoluble protein. This increase was considered statistically significant (p.001). A large variation among different tumors was noted. Also results varied with differences in time after ovariectomy. Under the same incubation conditions the same percentage of increase in the rate of 3H-leucine incorporation had been observed in the study of the effect of estrogen on the uterus of ovariectomized rats. In other mammalian tissues studied those containing high levels of estrogen receptor were able to respond to direct stimulation of estrogen. It was concluded that estrogen directly stimulates protein synthesis in the mammary tumors. This supports the view that these tumors are estrogen responsive tissues.

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