Measurement of the corticosteroid-binding globulin, progesterone, and progesterone "receptor" content in human endometrium.

The corticosteroid-binding globulin (CBG) content has been determined in cytosols prepared from human endometrium taken at different phases of the menstrual cycle, at 8-10 weeks gestation, and during treatment with an oral contraceptive. The data were compared to the progesterone "receptor" and the progesterone concentration in the same tissue extracts. The plasma contamination was estimated by the serum albumin content. It was observed that CBG is a constant contaminant of the endometrial cytosols. All of the CBG content can be considered to be of plasma origin. The cytoplasmic progesterone "receptor" content is between 21-33% of the CBG concentration during the menstrual cycle and is only 1% during pregnancy. The cytosol progesterone concentration is much higher in endometrium than would be expected from the plasma contamination and the level of the progesterone "receptor".