THE NATURE OF THE CIRCULATING THYROID HORMONE IN GRAVES' DISEASE 1

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Abstract
Studies of the plasma of 6 hyperthyroid patients 2-10 days following the admn. of therapeutic doses of radioactive iodine (I131) indicate that 97-99% of the labelled iodine is protein-bound. Methods are descr. involving trichloroacetic acid precipitation and butanol extraction for the quantitative separation from plasma of the labelled protein-bound iodine, and for its characterization by partition chromatographic technics using filter paper and cellulose columns with butanol-acetic acid-water and pentanol-pyridine-water solvent systems. Practically all of the labelled organic iodine in the plasma was found to exist as a single substance indistinguishable from thyroxine. No monoiodotyrosine, diiodotyrosine, or acetylthyroxine were detectable as constituents of the plasma protein-bound iodine. Evidently the circulating thyroid hormone in Graves'' disease is thyroxine.