Differential Effects of Estrogen and Prolactin on DNA Synthesis in Organ Cultures of DMBA-Induced Rat Mammary Carcinoma 1

Summary

Explants from mammary carcinoma of DMBA-treated Sprague-Dawley rats were cultured for 5 days in medium 199 containing insulin (5 μg/ml) and corticosterone (1 μg/ml). Estradiol-17β (0.0001–10.0 μg/ml) and/or ovine prolactin (5μg/ml) in various combinations were added to the media. Media were replaced at 2 and 4 days. ³H-thymidine (0.5 μCi/ml) was added to each group of cultures 4 hr prior to termination and its rate of incorporation into DNA was used in the assessment of DNA synthesis. A highly significant increase in incorporation of ³H-thymidine into DNA was obtained in the prolactin-treated cultures. Estrogen, at the lower levels (0.0001–1.0 μg/ml) or at the higher levels (5.0–10.0 μg/ml), was without significant effect or inhibitory, respectively, to DNA synthesis. These data demonstrate an important role for prolactin in stimulating DNA synthesis in vitro, in contrast to estrogen, which was consistently found to be without stimulatory effect.