Endometrial estrogen and progesterone receptors within 2-14 days of missed menses in the human

Serial changes in the endometrial levels of estrogen and progesterone receptors (ER and PR) were measured in 50 women from days 2 to 14 of missed menses and correlated with the plasma concentrations of hCG, progesterone and 17 beta-estradiol. Both ER and PR of nuclei were higher than cytosolic proteins, with a shift in the ratio of nER/nPR to nPR from 4th day after missed menses. On Scatchard analysis of the cytosolic and nuclear binding proteins, two classes of proteins, corresponding to Type I and II, were found. While the increasing levels of hCG maintained luteal secretion of progesterone and 17 beta-estradiol at normal mid-luteal phase levels, a gradual increase in 17 beta estradiol from 9th day of missed menses was noted. This delicate balance between circulating levels of progesterone and 17 beta-estradiol and their nuclear receptors at early stages of pregnancy may be of significance.