ABSTRACT
This chapter introduces an in vitro histochemical technique for localizing the intracellular estrogen binding sites in cryostat frozen sections of the rat uterus, using a macromolecular, hydrophilic, fluorescent estradiol conjugate as a histochemical reagent. Based on quantitation of the specific estrogen binding activity in the cytosolic and the nuclear fraction of tissue homogenates, the widely accepted general scheme of steroid-receptor interaction was developed. A major difference between the histochemical and the biochemical approach to studying estrogen receptors is that the former is concerned with receptors in relatively intact cellular or tissue fragments, and the latter with free receptor protein molecules. In a cytosol assay system, the concentration of the ligands bound to receptor proteins can never exceed the concentration of the free ligand initially added to the incubation mixture. In addition to the potential difference in physical properties between the soluble receptors and the tissue-bound receptors, there may be chemical differences between the two as well.
