Uteroglobin as a progesterone-binding protein in the preimplantation uterine epithelium of the rabbit: biochemical studies.

Progesterone binding was studied in the uterus of rabbits at two different hormonal stages; either after oestrogen priming or a short time before implantation of the blastocyst (162 h post coitum). Uterine cytosols were incubated with [3H]progesterone, or the labelled hormone was injected into the uterine lumen 1 h before killing the animals. Gel filtration, ion exchange chromatography, sucrose gradient centrifugation, isoelectric focusing and saturation analysis indicate that during the period prior to implantation, the uterine progesterone receptor disappears and progesterone binding is performed by uteroglobin. These findings support the hypothesis that the physiological role of uteroglobin in the reproductive process is connected with its hormone-binding ability.