Estradiol and progesterone receptors in human endometrium: normal and abnormal menstrual cycles and early pregnancy.

Estradiol and progesterone receptor sites (empty or filled with endogenous hormone)have been measured in the cytoplasm and nuclei of human endometrium. Receptor changes have been observed throughout the normal menstrual cycle. During the preovulatory phase the cytoplasmic estradiol receptor sites do not change while the nuclear receptor sites more than double. Cytoplasmic estradiol receptor sites decrease very early in the secretory phase, whereas the decrease in nuclear sites occurs later. Cytoplasmic progesterone receptor sites more than double during the preovulatory phase and show a large decrease immediately after ovulation, when the concentration of nuclear receptor is at its highest. Thus the total cellular concentrations of both estradiol and progesterone receptors are lowest in the late secretory phase. It was found that they are positively correlated with the concentration of plasma estradiol only during the proliferative phase. The concentration of cytoplasmic progesterone receptor is negatively correlated with 17 beta-hydroxysteroid oxidoreductase activity during the secretory phase. In anovulatory cycles the concentrations of estradiol and progesterone receptors are high, similar to those of the late proliferative phase. "luteal insufficiency" is characterized by a very low concentration of estradiol receptor. Early pregnancy endometrium (8 to 10 weeks' gestation) is characterized by a large concentration of progesterone receptor, exceeding those of any period of the menstrual cycle.