Cytosol and nuclear progesterone receptor in cat uterus and oviduct

Abstract

Binding of progesterone (P) to a specific cytosol receptor and the in vivo translocation of the cytosol receptor complex to the nucleus was studied in the cat uterus and oviduct. Cytosol and nuclear fractions were prepared from the reproductive tracts of ovariectomized animals treated for 14 days with estradiol (E 2) and from those which were subsequently infused with a P solution for 15 min. In vitro cytosol incubation with [ 3H]-P included cortisol to eliminate binding to CBG. The specific binding of [ 3H]-P reached equilibrium within 90 min at 0°C and was stable for at least 4 h in both tissues. Competitive binding studies revealed the following binding affinities for the cytosol receptor; R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione) = P ⪢ corticosterone = E 2 = testosterone. Scatchard analysis of [ 3H] P binding in cytosols from E 2-treated animals yielded a K D of 3.2 × 10 −8 M in the uterus and 2.5 × 10 −8 M in the oviduct. The P binding protein had a sedimentation coefficient of 6.8 S. The content of nuclear receptor was assessed by an exchange assay using R5020. Equilibrium was reached within 4 h at 22°C and remained unchanged for another 2h. The relative binding affinities for the nuclear receptor were; R5020 > P > corticosterone > testosterone > E 2. The K D was 8.2 × 10 −9 M in uterine nuclei and 6.0 × 10 −9M in oviduct nuclei from E 2 + P treated animals. Following P-infusion the decrease in the quantity of specifically bound [ 3H]-P in the cytosol, and the increase in the quantity of specifically bound [ 3H]-R5020 in the nuclei, were significant in both tissues.