Role of Plasma Proteins in the Binding, Distribution and Metabolism of the Thyroid Hormones

ALTHOUGH it has been recognized for many years that thyroxine is tightly associated with plasma proteins little attention was paid to this phenomenon until the discovery, in 1952, of thyroxine-binding globulin (TBG) by three groups of investigators working independently of each other.1 2 3 Subsequently, Ingbar4 described thyroxine-binding prealbumin (TBPA). These proteins together with serum albumin participate in the peripheral transport of the thyroid hormones. The concept of a multiple equilibrium between thyroxine bound to the plasma proteins and thyroxine in the unbound or "free" state was extensively developed by Robbins and Rall.5 These investigators suggested that the concentration of free thyroxine, . . .