Estrogen Action in the Mouse Uterus: Adrenal Modulation of Receptor Levels

Abstract

Adrenal regulation of estradiol receptor levels was demonstrated in the ovariectomized mouse uterus. After ovariectomy, cytosol receptor levels initially followed a cyclic pattern, with a periodicity of approximately 5 days and a range of range of 2.25-4.80 x 10(-13) mol estrogen receptor/100 micrograms DNA. Nuclear receptor levels showed marked fluctuations initially, but stabilized after day 15 at approximately 0.5 x 10(-13) mol/100 micrograms DNA. Microsomal receptor levels also changed with time, but at a lower level than the cytosol and nuclear fluctuations. Concurrent cyclic changes in uterine or vaginal histology were not observed. After simultaneous ovariectomy and adrenalectomy, cytosol estradiol receptor levels remained low (less than or equal to 1.5 x 10(-13) mol/100 micrograms DNA) from 5-24 days, with no fluctuations. Nuclear and microsomal receptor levels changed, but to a smaller extent than those in ovariectomized mice. Concurrent histological changes were not observed. The residual cytosolic estrogen receptor remaining in the ovariectomized-adrenalectomized mouse uterus was characterized. Scatchard analysis of saturation binding data showed one class of binding sites with a Ka of 6.56 nm-1 (n = 350 fmol/mg protein). This cytosol receptor sedimented at 8S on low salt sucrose density gradients. Receptor specificity was assessed by competitive equilibrium binding. The rank order of ligands was 17 beta-estradiol = diethylstilbestrol greater than nafoxidine. Progesterone and 5 alpha-dihydrotestosterone showed no appreciable binding activity. After the injection of estradiol (10 micrograms/kg), 80-90% of the total available estrogen receptor translocated to the nuclear compartment. This translocated receptor could stimulate uterine hypertrophy and hyperplasia, as assessed in 1- and 3-day bioassays, and was able to initiate progesterone receptor synthesis. From these results, we conclude that the adrenal can modulate uterine estrogen receptor levels.