THYROXINE DISPLACEMENT FROM SERUM PROTEINS AND DEPRESSION OF SERUM PROTEIN-BOUND IODINE BY CERTAIN DRUGS

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Abstract
The binding of thyroxine to human serum proteins has been studied by paper electro-phoresis in (NH4)2CO3 buffer at pH 8.4. Salicylate and 2,4-dinitrophen-ol inhibit thyroxine binding to prealbumin, the displaced thyroxine appearing in the thyroxine binding [alpha] -globulin area. Diphenylhydantoin inhibits thyroxine binding to the thyroxine-binding [alpha]-globulin, displacing it onto prealbumin. DL-tetrachlorothyronine displaces thyroxine from the thyroxine-binding [alpha]-globulin, and at high drug concentrations also from prealbumin. Tetrochlorothyronine given in vivo lowers the level of serum protein-bound iodine in intact and in thyroidectomized thyroxine-treated guinea pigs. It is concluded that loss of binding sites on either of the 2 major thyroxine-binding proteins can explain the lowering of the serum protein-bound iodine produced by the 4 drugs studied when they are given in vivo.