Immunological quantitation of rat and mouse thyroxine-binding globulins. Ontogenesis and sex-dependence of the circulating levels of the thyroxine-binding globulins.

We describe the preparation of monospecific antisera against a thyroxine-binding globulin partially purified from immature rat sera by affinity chromatography on thyroxine-Sepharose. The antisera are used for the rocket immunoelectrophoresis assay of rat thyroxine-binding globulin and also, owing to their partial cross-reactivity with mouse thyroxine-binding globulin, for the quantitation of this serum binding protein in the mouse. The thyroxine-binding globulin is measured in developing rats and in sexually mature male and female rats and mice. The results of the ontogenetic study confirm the postnatal surge of serum thyroxine-binding globulin levels, formerly demonstrated with binding techniques. They allow further to define the correlations, dependent on age, of the immunoquantitated thyroxine-binding globulin and transthyretin levels with the abilities of the sera to bind thyroxine. In sexually mature rats and mice we demonstrate an opposite sex-dependence of thyroxine-binding globulin levels, characterized by increased levels of the protein in the female rats versus increased levels of the protein in the male mice. This is the first report of immunological quantitation of rat and mouse thyroxine-binding globulins.