INTRATHYROIDAL IODINE METABOLISM IN THE RAT. THE INFLUENCE OF DIET AND THE ADMINISTRATION OF THYROID-STIMULATING HORMONE

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Abstract
Ratios of mono [I131] iodotyrosine and di [I131] iodotyrosine (R values) and the incorporation of I131 into iodothyronines have been estimated in rat thyroid glands from 30 min. to 38 hr. after the administration of [I131] iodide. In rats receiving a powdered low-iodine diet the R values were close to unity and did not change with time after the administration of [I131] iodide. In rats receiving a commercial pellet diet the R values fell from a mean of 0[center dot]8 at 30 min. after [I131] iodide administration to 0[center dot]49 at 38 hr. Administration of 0.5-2.0 i. u. of thyroid-stimulating hormone before giving the injection of [I131] iodide caused a small diminution in the R value when the time between injecting [I131] iodide and killing the animal was 16 hr. or more. Iodothyronines represented a greater percentage of the total thyroid-gland radioactivity in the iodine-deficient animals than in animals fed on the pellet diet. Thyroid-stimulating hormone had little effect, if any, on the iodothy-ronine contents.