Measurement of the Corticosteroid-Binding Globulin, Progesterone, and Progesterone “Receptor” Content in Human Endometrium*

Abstract

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".

Peer Review #1 of "Screening and identification of endometrial proteins as novel potential biomarkers for repeated implantation failure (v0.2)"

“…However, we found a lower level of serum progesterone in RIF patients, but the difference was not significant (Table 1) and a larger sample of research may be needed. The endometrial CBG content is thought to originate in the plasma (Kreitmann et al, 1978), thus, RIF patients may have a positive outcome with supplemental progesterone administration.…”