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Effects of a Hypothalamic Estrogen Implant on Growth of Carcinogen-induced Mammary Tumors in Rats¹

Department of Physiology, Michigan State University, East Lansing, Michigan 48823

Fifty-five-day-old Sprague-Dawley female rats were given an i.v. injection of 5 mg 7,12-dimethylbenz(a)anthracene, and 15 to 30 days after the appearance of palpable mammary tumors the rats were given (a) an estradiol benzoate (EB) implant in the median eminence (ME), (b) an EB implant outside the ME, (c) an EB implant in the cerebral cortex, or (d) a cholesterol implant in the ME. At 25 days after implantation, the average number of tumors per rat and percentage of increase in size and total weight of tumors in rats with an EB implant in the ME were significantly greater than in all other groups. This is attributed to the observed increase in serum prolactin levels as a result of the direct action of EB on the hypothalamus, pituitary, or both.

¹ This research was supported in part by NIH Grants CA 10771 and AM 04784.

² Postdoctoral Research Fellow of the International Agency for Research on Cancer, World Health Organization.

Received 8/20/69. Accepted 12/ 4/69.