Thyroxine Displacement From Serum Proteins and Depression of Serum Protein-Bound Iodine by Certain Drugs

A number of compounds such as 2,4-dinitro-phenol, ' salicylate, tetrachlorothyronine, and di-phenylhydantoin have been shown to lower the protein-bound iodine level of the blood (1-5). In the case of DNP and salicylate, it was concluded that they acted in part via an inhibition of the pitu-tary TSH mechanism and partly by an accelerated loss of T4 from the circulation (2, 6). A likely site of action was, therefore, expected to involve binding of T4 to serum proteins. The ability of various analogs of thyroxine to bind to proteins of serum has been extensively studied with electrophoretic techniques. At least three serum proteins and perhaps four have been described which bind thyroxine (7). Less direct