Estriol-induced dose-dependent DNA synthesis in normal human mammary epithelium in vitro.

Normal human adult resting mammary gland explants were cultured during 7 days. The influence of hormones on DNA synthesis was assessed by autoradiography after incubation with tritiated-thymidine. Estriol was added to the medium at 3 different concentrations. With 0.01 ng/ml the labeling index remained at the level observed in the controls in the basic unenriched medium. A 10- and 100-fold increase of estriol elicited a transient, significant and dose-related increase of DNA synthesis on the 2nd day of organ culture. Estriol gave a qualitatively different profile of DNA synthesis than estradiol at 1.0 ng/ml. The results are compared with the effect of progesterone.