The ontogeny and cellular distribution of estrogen receptors in normal mouse mammary gland

The appearance, epithelial and stromal cell distribution of estrogen receptors (ER) in normal mouse mammary gland were determined between 1 and 10 weeks of age using immunohistochemistry. The effect of ovariectomy and estrogen (E)-treatment on the distribution and concentration of ER-positive cells at various ages was also analyzed. These studies demonstrate that ER are present in both mammary epithelial and stromal cells before the mammary gland exhibits a proliferative response or increase in progesterone receptor concentration as a result of E-treatment. Furthermore, an analysis of E-treatment suggests that although ER are present at an early age, there may be additional factors that determine the nature and extent of E-responsiveness.