Loss of differentiative potential of the mammary gland in ovariectomized mice: Altered estrogen responsiveness in parous mice

Abstract

Previously, estrogen had been shown to be essential for the maintenance of differentiative potential in the mammary gland of virgin mice; the purpose of this study was to evaluate the role of these steroids in nonpregnant, nonlactating parous mice. To this end, parous mice were either ovariectomized or adrenalectomized and ovariectomized for 4–6 weeks before hormonally induced differentiation was attempted in culture. Although mammary glands from virgin mice lose their differentiative potential in vitro following ovariectomy, tissue from castrated parous mice exhibit only a partial loss of activity. Since combined adrenalectomy and ovariectomy in parous animals virtually abolished differentiation and since exogenous estradiol preserved it, it would appear that mammary gland differentiation in parous mice, as in virgins, requires estrogens, but that tissue from the former is more sensitive. This difference between virgins and parous mice is not related to differences in either the capacity or affinity of the cytosol estrogen receptor, as these parameters are identical in all experimental groups.