Abstract
Summary
The effects of estradiol and ovine prolactin on the growth of a rat mammary adenocarcinoma cell line were investigated. The action of estradiol was dose-dependent. At ±1 μg/ml it did not influence growth, at 5-10 μg/ml it was inhibitory, and at 20 μg/ml it was toxic. Prolactin alone had little effect on growth. However, the inhibitory effect of estradiol could be counteracted by a high concentration of prolactin. It appears, therefore, that the growth of cultured rat mammary adenocarcinoma cells can be regulated by the ratio of prolactin to estradiol: When the ratio is high growth is favored; when it is low, growth is inhibited.
We thank Dr. J. H. Weisburger for his critical review of the manuscript; the Hormone Distribution Program, National Institute of Arthritis, Metabolic and Digestive Diseases for the generous supply of ovine prolactin; and Ms. Michele Soyer and Dr. P. Hill for estrogen assays. Supported in part by Public Health Service Research Grant No. CA 012376 from the National Cancer Institute.
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