The proliferative action of oestriol.

Daily injections of oestriol, spanning a wide dose range, produced mitotic responses in the uterine luminal epithelium of mice. At the higher doses the response was comparable to that obtained with oestradiol. The maximum response occurred on day 1, after which mitosis was significantly reduced on days 2 and 3. This reduction in mitosis following an initial peak was seen at all doses and was not therefore consequent on a critical cell number being reached. Proliferation was also induced in the basal epithelium of the vagina, though to a lesser extent. Oestriol and progesterone together stimulated DNA synthesis and mitosis in the epithelium of the mammary gland.