A specific progesterone receptor in the hamster uterus: physiologic properties and regulation during the estrous cycle.

Abstract

Our previous studies indicated the presence of an estrogen-dependent, progesteronebinding system in the hamster uterus. A progesterone- binding component has now been characterized in the uterine cytosol fraction by density gradient centrifugation (6–7S sedimentation coefficient in sucrose-glycerol gradients), binding equilibrium measurements (KA = 1.7 ± 0.08 × 109) M−1) and competition assays. The hormone specificity of the progesterone-binding component was indicated by the relative binding activity of progesterone (100), deoxycorticosterone (64) and 5α-pregnanedione (20). Other hormonal steroids tested or progesterone metabolites did not compete effectively for :3H-progesterone-binding sites. The concentration of progesterone-binding sites in uterine cytosol was calculated from Scatchard plot analysis of data obtained by a dextran-charcoal adsorption method. During the estrous cycle, fluctuations in the concentration of progesteronebinding sites on a wet weight, cytosol protein or DNA basis were correl...