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.
IT HAS been demonstrated that hypothalamic-adenohypophyseal regulatory mechanisms maintain the production and release of thyroid hormone within euthyroid limits (1, 2). Previous observations from this laboratory have indicated that without exogenous thyroid or iodide intake the protein-bound iodine in healthy adults remains relatively constant (3). Granting adequate analytic precision, such constancy is compatible with, but does not necessarily support, the existence of a “feed-back” mechanism activated by changes in the plasma level of thyroid products. Introduction of exogenous thyroid products into such a system should provide evidence, however, concerning the presence and the efficiency of such adaptive responses. This report describes the effects of thyroid feeding on serum protein-bound iodine levels and other pertinent indices in euthyroid adult males. PROCEDURES Desiccated thyroid of the same lot number1 was administered in amounts ranging between 1 and 6 grains per day to 9 presumably healthy adu...
