ヨードによる甲状腺のヨード有機化阻害に関する研究
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TSH has an accelerating function in iodine-metabolism of thyroid, but it is known that, on the contrary, such an action of TSH does not appear, when the plasma iodine concentration increases remarkably.<BR>In these experiments, the inhibitory effects on organic binding of iodine in thyroid of rats were observed under various conditions of TSH secretion, and iodinated organic compouds in thyroid and plasma of rats, of which the inhibitory effect was found, were analysed to investigate the components.<BR>Rats (weighing 90 to 250 g) were fed on a low iodine diet and administrated with 0.02% Mercaptoimidazole solution as drinking water for 14 to 21 days. Three days after stopping the administration of the goitrogen solution, rats were injected with various amounts of iodine in the form of KT labeled I<SUB>131</SUB>, then 6-12 hours later, the rats were sacrificed, and the radioactivity of the thyroid was counted by a well-type scintillation counter. The thyroid was ground in an all glass homogenizer with saline. The homogenate was divided in two parts, one part was centrifuged once with 10% TCA and washed twice with 5% TCA. The radioactivity of the precipitate (organically bound iodine) was measured, and the amouts of organically bound iodine<SUP>17</SUP> were caluculated from the ratio of organically bound iodine<SUP>131</SUP> to the total radioactivity. The other part was centrifuged with saline in Spinco L-type ultracentrifugator for 80.000 g × 30 minutes, and the supernatant fraction obtained was filtered through Dowex I × 2,200-400 mesh in order to remove inorganic iodine, and then the organic iodine "was measured.<BR>Blood, whose organic binding of iodine was blocked, was subjected to the following procedures : a) Inorganic iodine was removed from plasma by the use of Dowex 1. After passage through the resin, the radioactivity of organically bound iodine (PBI<SUP>131</SUP>) and that of butanol inextractable iodine (BII<SUP>131</SUP>) in PBI<SUP>131</SUP> was measured. b) The plasma was passed through Dowex 1 with acetate buffer at pH 5.6 and and BII<SUP>131</SUP> fraction was gained. The BII<SUP>131</SUP> fraction was digested with trypsin-and pancreatin, and the iodinated components of the fraction were investigated.<BR>The results were as follows : <BR>1) Under the endogenously-increased TSH secretion condition : <BR>Organic binding of iodine in the thyroid gland was blocked remarkably when the level of plasma inorganic iodine rose above 6-12r% with the administration of large amounts of iodide in rats which had been treated with goitrogen, which treatment had had ended 3 days previously.<BR>2) Under the condition of increased TSH level with large doses of exogenous TSH.<BR>Two USP of TSH and excess iodide were injected into untreated rats intraperitoneally ; eight and twelve hours later the thyroid and blood were obtained, and then subjected to the procedure described above. Also in these cases, organic binding of iodine in thyroid was blocked over 6γ% of plasma inorganic indine level.<BR>3) Under the condition of normal TSH secretion.<BR>In untreated rats (TSH is thought to be secreted normally by the pituitary.), organic binding of iodine was not blocked until the plasma inorganic indine level increased to 33y% with large doses of iodide.<BR>4) PBI<SUP>131</SUP> fraction when organic binding of iodine was blocked.<BR>In all cases, blocked organic binding of iodine in the thyroid glands with large doses of iodide, the ratio of BII<SUP>131</SUP> to PBI<SUP>131</SUP> in plasma increased to 50-80%, whereas the BII<SUP>131</SUP> ratio to PBI<SUP>131</SUP> in the plasma of rats, whose glands were not blocked but organic binding of iodine in thyroid, was always below 25%<BR>5) The administration of large amounts of iodine to thyroidectomized rats.<BR>Thyroidectomized rats received large amounts of iodine, and after 8 hours the blood was obtained for analysis. In this experiment,
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