大量ヨードによる実験的甲状腺腫に関する研究:甲状腺内サイロニン合成率の低下
スポンサーリンク
概要
- 論文の詳細を見る
The effects of large doses of iodine on thyroid weight and the hormone synthesis was studied in chick and rat with the aid of <SUP>131</SUP>I and chromatographic analysis.<BR>Male and female Whiet-Rock chicks weighing 900 to 1500 g. were fed on a standord diet throughout the experiments. In order to determine the effect of a single dose of excessive iodide, chicks were given an intraperitoneal injection of 100-200 μc <SUP>131</SUP>I with carrier 1.0 mg. iodide. Thyroids were removed and analysed at an appropriate time after the injection. Control chicks were injected 10-20 μc <SUP>131</SUP>I alone and sacrificed at the corresponding time. Long-term treatment with iodide was carried out as follows : Chicks were given about 1.0 mg. iodide every day for the last 4 weeks. and each one was injected 1.0 mg. iodide together with 200 μc <SUP>131</SUP>I. The thyoids were removed at 4 and 24 hours 1 after <SUP>131</SUP>I.<BR>For the comparison among different species, male Wistar rats weighing 100-150 g. were also fed on a low iodine diet throughout the experiments. The method was the same as used in chicks, but the quantity of iodide was 500 sg. and the duration of iodide treatment was 3 weeks.<BR>Other experiments were studied with chicks at 1, 3 and 9 weeks after withdrawal of a long-term treatment of iodide for the study of residual effect of the treatment. In these experiments, chicks were sacrificed at 4 hours after the injection of carrier free <SUP>311</SUP>I.<BR>Radiochromatographic analysis of the thyroid tissue after enzymatic hydrolysis was performed either by paperchromatography or columu chromatography using Pileggi's modification.<BR>Long-term treatment of iodide for 4 weeks induced a significant increment of the thyroid weight in chick; about 1.8 times greater than the controls. Histology of the goiter showed flat epithels and marked colloid storage within large follicles. While the 3-week treatment of iodide failed to produce goiter in rats.<BR>In both animals, it was shown on chromatogram of the thyroid that a single of carrier iodide resulted in a significant but transient reduction of organic <SUP>131</SUP>I and thyronine <SUP>131</SUP>I proportion as well as an elevation of <SUP>131</SUP>I MIT/DIT ratio. After a long-term treatment of rat with iodide, an "escape" occured from this inhibitory effect of iodide; formation of thyronines was resumed with recovery of organification of iodide and MIT/DIT ratio, as previously reported by Pitt-Rivers et al. On the contrary, in the goitrous chicks continuo usly treated with iodide, synthesis of thyronine <SUP>131</SUP>I was significantly depressed notwithstanding the presence of normal proportion of organic <SUP>131</SUP>I and rather lower MIT/DIT ratio than controls.<BR>After a 3-week withdrawal of iodide feeding, MIT/DIT ratio recovered first. The depressed thyronine <SUP>131</SUP>I synthesis as well as increased thyroid weight had not returned to control levels until 9 weeks after stopping the iodide treatment.<BR>It appears that the depressed rate of thyronine synthesis would be a cause of the goiter through the negative feed-back mechanism in iodide-fed chicks.
- 日本内分泌学会の論文