Effects of estradiol and prolactin on growth of rat mammary adenocarcinoma cells in monolayer cultures.

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 less than or equal to 1 mug/ml it did not influence growth, at 5-10 mug/ml it was inhibitory, and at 20 mug/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.