Enhanced inhibition of estrogen receptor nuclear binding in the uterus of aged mice.
We have studied why uteri from aging mice show a decrease nuclear concentration of estrogen receptors (UER). While 50-60% of available cytosolic UER from ovariectomized (OVX) mice aged 4-8 months, upon physiochemical activation, are able to bind either to DNA-cellulose or nuclear suspensions from young animals, only 20-30% of comparable concentrations of cytosolic UER from mice aged 15-18 months did so under identical experimental conditions. Nuclear dilutions with uterine cytosolic fractions from estrogen treated OVX mice prior to determination of [3H] UER binding sites in nuclear suspensions decreased the number of nuclear ER sites in both age groups. However, we observed that cytosols from aged animals showed a greater ability to prevent [3H]E2 binding to nuclear sites when compared to young ones (inhibition index: 0.286 +/- 0.013 (SE) vs. 0.137 +/- 0.025, P less than 0.05). These changes occur independently of protein concentration and result from dilution of a specific endogenous inhibitor of [3H]E2 binding to nuclear sites. The significance of these observed differences is discussed.
D000375:Aging / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D010052:Ovariectomy; D011960:Receptors, Estrogen / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism*
D011960:Receptors, Estrogen; D004958:Estradiol; D004247:DNA