Oestradiol receptors and histogenesis in normal female breast of Holtzman rat.

This paper embodies observations on the specific oestrogen receptor concentrations and histogenesis in the breast tissues of female Holtzman rat from day 10 of birth to day 260. It is noted that up to day 60, even though the normal differentiation and morphological growth of mammary tissue is in progress, oestradiol receptors are not detected. On the contrary, during this period maximum receptor concentrations have been observed in another target tissue viz. uterus. After day 60, it is the uterus which shows minimal amounts of receptors, while the breast tissue has appreciable amounts of receptor proteins. During this period, the morphological growth of the breast is maximum and this ceases apparently by day 90. Repeated estimations fail to reveal any receptors between days 73 to 87 and this phenomenon cannot be explained at present. Similarly from day 140 onwards no oestradiol receptors are evident. This probably is the cut off point for the receptors in the normal rat breast tissue.