Progesterone Binding in the Mouse and Rat Uterus1

Progesterone—binding components in the uterine cytosol from the mouse and rat have been detected using sucrose—glycerol gradient analysis. The binding components in mouse uterine cytosol had sedimentation values of 4S and 6.5S and for the rat, values of 4S and 7S were determined. The binding components in both species were found to be specific for the uterus and to be protein in nature. The amount of binding was dependent upon the endocrine status of the animal. Castration destroyed the binding components, but they could be restored to intact levels following estrogen stimulation. Competition studies showed a high specificity for progesterone and that little of the progesterone binding was due to contamination by corticosteroid binding globulin (CBG). Equilibrium measurements have indicated a high affinity of the receptor—hormone interaction (Kd 10-8 – 10-9M) while kinetic measurements have revealed a very rapid dissociation of the receptor—hormone complex which could be stabilized somewhat by glycerol. T...