L-Diiodotyrosineの代謝に関する研究:第1編 I<SUP>131</SUP>標識L-Diiodotyrosineの甲状腺および末梢に於ける正常の代謝
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I. In vitro deiodination of I<SUP>131</SUP>-labeled L-diiodotyrosine by slices of cow's thyroid.<BR>In this study the thyroidal deiodination of I<SUP>131</SUP>-labeled L-diiodotyrosine and the effect of various agents on the deiodination were observed.<BR>I<SUP>131</SUP>-labeled L-diiodotyrosine (L-DITI<SUP>131</SUP>) of high specific activity was incubated with slices prepared from cow's thyroids. Metabolic changes in the L-DITI<SUP>131</SUP> were recorded by paperchromatography.<BR>1. Labeled L-DIT was rapidly metabolized by thyroid tissues. The principal metabolic product was inorganic labeled iodide. There was no evidence of any deamination, and no other metabolic products were detected. The formation by tissue of labeled thyroxine or triiodothyronine seemed unlikely, but it may be that some of the labeled iodide released by the deiodination of L-DIT I<SUP>131</SUP> is incorporated in thyroglobulin.<BR>2. Deiodination was significant at 1/2 to 3 hours but further deiodination occurred between 4 and 6 hours.<BR>3. Inorganic labeled iodide formed from L-DITI<SUP>131</SUP> was roughly proportional to the wet weight of tissue.<BR>4. Carrier L-DIT at 12.8×10-3μg. per mg. of tissue inhibits deiodination of L-DI<SUP>131</SUP><BR>5. A nitrogen atmosphere did not inhibit deiodination. This indicates that neither tissue respiration nor glycolysis need be intact for deiodination.<BR>6. The addition of TSH to the medium had no effect on deiodination, indicating that TSH has no direct acute effect on tissue preparations.<BR>II. Metabolism of T<SUP>131</SUP>-labeled L-diiodotyrosine administered to normal human subjects.<BR>The metabolism of I<SUP>131</SUP>-labeled L-diiodotyrosine (L-DITI<SUP>131</SUP>) was studied in 7 normal subjects after intravenous injections of 50-120μc. of L-DITI<SUP>131</SUP> in 10-25μg. of L-DIT. Serial fractionation procedures were performed on samples of blood and urine.<BR>1. Labeled L-DIT disappeared rapidly from the blood and was replaced by labeled iodide.<BR>2. The percentage of the labeled iodine present as L-DIT<SUP>131</SUP> decreased with successive urine samples, and was negligibly small after 8 hours.<BR>3. Most of the administered dose was excreted as iodide. All of the subjects excreted 1.26 to 2.91 per cent of the L-DITI<SUP>131</SUP> in an unchanged form within 8 hours after injection.<BR>4. The high rate of disposal of L-DITI<SUP>131</SUP> estimated from the curves of serum concentration and urinary excretion was considered to be most consistent with a per peripheral deiodination process.<BR>5. The concentration of labeled iodine in serum diminished with great rapidity during the first 24 hours, but increased slowly after 48 hours. This indicates that the iodide released by the deiodination of L-DIT is utilized by the thyroid to synthesize thyroid hormone.<BR>6. The metabolism of L-DITI<SUP>131</SUP> was restudied in one of the subjects after a period of thyroid therapy, and it was proved that the treatment appeared to make no difference in the results.
- 一般社団法人 日本内分泌学会の論文