Sex hormone binding globulin: binding capacity and studies on the binding of cyproterone acetate and other steroids.

Sex hormone binding globulin in blood is quantitated by ammonium sulphate precipitation technique with two radioactive ligands, [3H]testosterone and [3H5dihydrotestosterone. Plasma levels in normal men, normal women, women taking oral contraceptives containing oestrogens, and pregnant women are presented, measured with both ligands. Binding experiments with these ligands and several competing steroids show marked differences in displacement ability. For cyproterone acetate 100-500 ng per tube is required to obtain even a slight displacement of the radioactive ligands.