RADIOACTIVE IODINE AS AN INDICATOR OF THE METABOLISM OF IODINE V. THE EFFECTS OF HYPOPHYSECTOMY ON THE DISTRIBUTION OF LABELED THYROXINE AND DIIODOTYROSINE IN THYROID GLAND AND PLASMA1

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Abstract
The conversion of iodide to diiodotyrosine and thyroxine-like fractions was compared in normal and hypophysectomized rats with radioiodine as indicator. At the early intervals, the % of the administered I found in the thyroid gland was much less in the hypophysectomized than in the normal rat. The conversion of iodide to diiodotyrosine is shown to occur readily in the hypophysectomized rat. Approx. 80% of the thyroid''s I was found in the diiodotyrosine-like fraction in the hypophysectomized rat. An appreciable portion of the plasma''s I was also present as diiodotyrosine. The % of the thyroid''s I present as thyroxine was much less in the hypophysectomized than in the normal rat. In the normal rat the plasma I was rapidly converted to thyroxine so that at 96 hrs. about 80% of the plasma''s I was found as thyroxine. In the hypophysectomized rat the % of plasma''s I found in the thyroxine-like fraction was negligible throughout the entire 96 hrs. of observation. It is suggested that in the hypophysectomized animal the conversion of iodide to diiodotyrosine is not severely interfered with, but that the over-all conversion of iodide.to thyroxine is limited.