ENDEMIC GOITER IN THE UELE REGION. 11.SYNTHESIS AND SECRETION OF THYROID HORMONES*

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Abstract
A study was made of the labeled iodinated amino acids and the specific activities of organic iodine in the thyroid and blood of 14 goitrous euthyroid patients of the Uele endemic area (Africa). Partial thyroidectomy was performed three to ten days after administration of I131. The total iodine content of the thyroid was in the normal range, but the concentration of iodine per gram was reduced to about 25 per cent. Although the thyroidal uptake of I131 was increased in all the patients, the level of plasma PBI131 was low in some cases (0.05 per cent of the dose per liter at twenty-four hours), and much higher in others (0.44 per cent). In the 8 "low PBI131" patients the isotopic equilibrium between the thyroidal and extrathyroidal organic iodine pools had not been reached seven days after administration of I131, whereas in the 6 "high PBI131" patients the specific activity of the organic iodine was two to seven times higher in the blood than in the thyroid gland. In the first group, there was a slowing down of the hormonal secretion rate. In the second group, the high PBI131 levels suggest the existence of an iodine pool with a fast turnover, functionally different from the rest of the thyroidal iodine stores. Chromatographic analysis of thyroid tissue after hydrolysis showed an increase of the MIT131 VIT131 ratio and a decrease in the labeled iodothyronine fraction. This distribution was probably the result of a diminution in the rate of transfer of I131 into the more heavily iodinated compounds. From this study it appears that besides an increased thyroidal iodine uptake, severe iodine deficiency induces several abnormalities in the synthesis and excretion of the thyroid hormone.