Direct influence of the three natural estrogens on human mammary gland in vitro

The direct influence of the three basic natural estrogens, estrone, 17 beta-estradiol and estriol, on DNA synthesis in human normal mammary epithelial cells was investigated in organ culture during 7 days, and was assessed by autoradiography. A threshold concentration of I.O. ng per ml was needed to elicit a significant stimulation by estradiol and estriol. No significant increase in the incorporation of tritiated-thymidine could be obtained with estrone in the same conditions. These observations are in keeping with the hypothesis put forward by Gurpide, Tseng and Gusberg (1977) that estrone per se might be devoid of any direct estrogenic effect.