Protein-Bound Iodine in Serum of Rats Receiving Iodide or Iodine With or Without Goitrogen*†

DVOSKIN&S studies with elemental iodine (1, 2, 3) clearly established that injections of this form of the halogen were as effective as thyroxine or desiccated thyroid in cancelling the inhibition of growth which followed thyroidectomy or goitrogen therapy in immature rats. Subsequently Barker showed that administration of elemental iodine by the subcutaneous route produced marked elevations of the protein-bound or precipitable iodine in the plasma of rats and in the tissues at the sites of injection (4, 5). In the experiments reported by Dvoskin, parenteral or oral inorganic iodide proved to be essentially inert in restoring or maintaining normal growth rates in hypothyroid or athyroid rats. These findings are of particular interest, since Chaikoff had observed (6) that in rats fed inorganic iodide the protein-bound iodine of serum also rose, though these rises were of lesser magnitudes than those described in Barker's work. Our own studies in this field (7–10), conducted in humans, indicated that oral feeding of potassium iodide in massive or even in ordinary therapeutic amounts raises the nonthyroxine fraction of the protein-bound iodine without producing hypermetabolism.