The Study of Endemic Goiter in Hokkaido (The 3rd Report)

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  • OHTAKI Sachiya
    The 2nd Department of Internal Medicine, School of Medicine, Hokkaido University

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Other Title
  • 北海道地方の海岸性甲状腺腫の研究 第3報
  • 北海道地方の海岸性甲状腺腫の研究-3-
  • ホッカイドウ チホウ ノ カイガンセイ コウジョウセンシュ ノ ケンキュウ 3

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Abstract

The previous reports showed that the prevalence of goiter was comfirmed on the coast of Hokkaido, the northern island of Japan, where the usual diet of the inhabitants contained a large quantity of “iodine-rich” seaweed. Some of these goitrous patients from the endemic coast revealed high plasma inorganic iodine level and marked increment of thyroidal iodine space and thyroidal iodine content. However, all the goitrous patients from the endemic coast were clinically euthyroid, and serum total cholesterol level, protein bound-iodine and basal metabolic rate were within normal ranges.<BR>The present investigation is designed to elucidate a mechanism of the synthesis of thyroid hormone in the goitrous patients from this endemic coast.<BR>1. Thiocyanate test was examined in twelve goitrous patients from the endemic coast by the method of Floyd et al. In all the six patients taking their usual diet marked discharge of I131 from the thyroid following intravenous administration of thiocyanate, while no discharge was found in any of the remaining six patients one week after withdrawal of seaweed from the usual diet.<BR>2. Metabolism of I131 -labeled L-diiodotyrosine (L-DIT I131) was studied in five goitrous patients from the endemic coast put on the usual diet and three control patients after intravenous injections of L-DIT I131 by the method of Stanbury et al. All the patients from the endemic coast excreted 2.7 to 6.2 per cent of L-DIT I131 in an unchanged form within four hours after injection. Three control patients excreted 2.3 to 5.0 per cent.<BR>3. Radiochromatographic analysis of thyroid tissue was performed in seven goitrous patients from the endemic coast and two control patients with a single adenoma by Suzuki's modification of the method of Roche et al. All the patients were put on “iodine-restricted” diet for one to three weeks before partial thyroidectomy. Removal of thyroid tissue was carried out at twenty four hours after oral administration of carrier-free I131. Paranodular tissue was analyzed in control patients. The solvents used were butanol-acetic acid-water (78 : 5 : 17) in descending phase and butanol-dioxaneammonia (4 : 1 : 2) in ascending phase. The ratios of radio-monoiodotyrosine to radiodiiodotyrosine (MIT/DIT) ranged from 1.1 to 3.3 in all the goitrous patients from the endemic coast, and the proportions of radio-thyroxine plus radio-triiodothyronine (T4 + T3) ranged from 1.3 to 6.0 per cent in all but one. Control subjects represented 0.5 to 0.8 in the MIT/DIT ratio and 10.7 to 20.4 per cent in the proportion of T4+ T3.<BR>Significant discharge of I131 from the thyroid, as well as the previous report of dynamic analysis of stable and radioactive iodine, indicates that a large quantity of iodine remained as an inorganic form and suggests a markedly decreased rate of organification of I131 in the patients with seashore goiter taking the usual diet. Similar abnormalities were shown also in the iodide goiter reported by Paris et al.<BR>From the results of urinary excretion of L-DIT I131, it is found that there is no defect at least in peripheral deiodination of iodotyrosine in the seashore goiter.<BR>Radiochromatographic analysis obtained from the thyroid tissues of the seashore goiter indicates a diminution in the rate of transfer of I131 the more heavily iodinated compounds. Similar abnormal patterns had, however, been demonstrated in various thyroid disorders. It is, therefore, unlikely that such increase in the MIT/DIT radio and decrease in the proportion of T4 + T3 are peculiar to this goiter.<BR>In summary, these data would appear to support in part our thesis that the excessive and longstanding intake of dietary iodine is the most important goitrogenic factor of the seashore goiter in Hokkaido.

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