17-β-estradiol treatment maintains differentiative potential of virgin mouse mammary gland in culture and its responsiveness to insulin

Abstract

Abstract. Synthesis of the milk proteins, casein and α-lactalbumin was not induced in cultured mammary explants from C3H/HeN castrated virgin mice in the presence of lactogenic hormones such as insulin, cortisol and PRL. Replacement therapy with 17-β-estradiol to the castrated mice completely restored the differentiative potentials of mammary explants, inducing synthesis of the two milk proteins. [3H] thymidine incorporation into DNA synthesized in cultured mammary explants was also decreased by castration to less than 50% (P< 0.001) of that obtained in intact mice, and 17-β-estradiol treatment to castrated animals restored DNA synthesis to 90% of the intact level. The addition of insulin to culture medium significantly (P< 0.001) enhanced [3H] thymidine incorporation into DNA in cultured mammary explants from both intact and 17-β-estradiol-treated castrated mice but not from castrated animals. Insulin binding sites (1710 ± 260 sites/cell) to mammary epithelial cells from castrated mice were significantly (P<0.05) lower than those from both intact (2870 ± 300 sites/cell) and 17-β-estradiol-treated castrated animals (2860 ± 190 sites/cell). The present findings suggest that 17-β-estradiol maintains growth and differentiative responses of mammary epithelial cells to insulin, which may be through preserving the number of insulin binding sites in the cells.