ORGANIC AND INORGANIC IODINE: THEIR RECIPROCAL METABOLIC FATES*†

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Abstract
The mutual inter-conversion of iodide and organic iodine in the organism has been studied in man and in rats. Both stable and radioactive compounds were employed. The organic compounds used were derivatives of diiodotyrosine, including phenyl diiodohydroxy phenyl propionic acid ("Priodax"). With these organic compounds a prompt and progressive liberation of iodide complicates their metabolic history. Such sources of exogenous iodine lead to "spurious" increases in the protein-bound iodine of the serum, so that clinical diagnostic confusion may result because the reported value is not truly "hormonal", i.e., of thyroid origin. Through suitable precautions such complications usually can be circumvented. The dosage employed (intraperit.) corresponded to 0.5 mg. I2 per 100 g. rat. At this dosage, whereas diiodotyrosine was largely deiodinated within 1 hr., the phenyl diiodohydroxy phenyl propionic acid ("Priodax") retained its I for several hrs. Moreover it was concd, by the liver preferentially.