A new assessment of subcellular distribution of bound estrogen in the uterus

Abstract

The experiments to be described demonstrate that the levels of estradiol-receptor complex † † The term estradiol-receptor complex is used here to describe the specific estradiol binding protein(s) of the uterus. present in uterine cytosol after whole tissue incubations at 0° or 37° are much lower than previous estimates. This discrepancy appears to be due to free estrogen trapped extracellularly which binds to the receptor upon disruption of the cells during homogenization. The time course of estradiol binding to cytosol and nuclear fractions at 37° shows that the amount of bound estradiol in the cytosol is very small relative to the total bound estradiol, and suggests that the transfer of estradiol binding sites from cytosol to nucleus is a very rapid process. Incubations at 0° indicate that the entry of estradiol into the uterine cell is markedly temperature-dependent.