The Influence of Extracellular Thyroxine-Binding Protein upon the Accumulation of Thyroxine by Tissue Slices 12

Abstract

The thyroxine-binding proteins for diverse human extracellular fluids were localized by zone-electrophoretic techniques. In vitro experiments to assessed the significance of extracellular proteins in the partition of thyroxine between cellular and extracellular phases. Model systems were devised with surviving slices of liver, heart, and kidney cortex and with suspending media containing human plasma fractions of varied thyroxine-binding potencies. "Uptake" of thyroxine by tissues in vitro was not dependent upon cellular metabolic activity, and thyroxine distribution, in such systems, could be formulated in terms of a reversible binding equilibrium between cellular and extracellular thyroxine-binding components. Possible implications of the data for the net transcellular flux of thyroxine in vivo were discussed.