SIMULTANEOUS MEASUREMENT OF THE IODIDECONCENTRATING AND PROTEIN-BINDING CAPACITIES OF THE NORMAL AND HYPERFUNCTIONING HUMAN THYROID GLAND*

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Abstract
IT IS generally agreed that the remarkable ability of the thyroid gland to accumulate iodine depends upon two successive, though perhaps related actions of the gland. First, inorganic iodide from the plasma is highly concentrated within the gland and second, thyroidal iodide is oxidized and bound to an organic moiety (1–5). When either of these functions is abolished, the thyroid gland fails to accumulate or to retain iodine (6–8). Since both appear to be rate-limiting factors in the production of thyroid hormone, methods which measure over-all iodine accumulation must reflect their combined activity. It would, therefore, appear useful to measure each of these functions individually, and to assess their importance in the initiation of abnormal, or the maintenance of normal thyroidal function. Methods have been devised for the measurement in vivo of the ability of the gland to concentrate inorganic iodide. Such methods depend on the complete inhibition of protein-binding of iodine, using pharmacologic agents or large doses of inorganic iodine (9, 10). Measurement of the rate of protein-binding of concentrated iodide has not been possible, however. This measurement must rest upon a knowledge of the quantity of concentrated iodide, a quantity which heretofore could not be determined unless protein-binding were completely inhibited.