Nature of plasma iodine following destruction of the rat thyroid with I131.

The method of filter paper chromatography has proved exceedingly useful in studying the nature of plasma iodine in animals injected with carrier-free doses of I131. The sensitivity of this method is such that an analysis can be carried out with less than 0.001 y of plasma iodine. Through application of this method, it has now been established that circulating iodine in the normal rat (l-3) and in the hyperthyroid human (4) consists primarily of thyroxine and inorganic iodine. It became of interest to determine whether, under certain conditions, other iodine compounds known to be present in the thyroid gland might appear in plasma. Destruction of the thyroid gland of the rat by internal radiation with In1 was known to produce an elevation in the protein-bound iodine level of the plasma (5), and it appeared likely that, under these conditions, iodine compounds other than thyroxine and inorganic iodine might be found in plasma. The present report deals with this possibility.