Abstract

The effect of 5 u.s.p. units of thyrotropic hormone (TSH) on the accumulation of radioactive iodine (I131) by the thyroid was studied in 12 cases of thyrotoxicosis. All the patients showed an increase in the thyroidal clearance rate after administration of TSH, the average increase being 30 per cent above the initial value. The change in accumulation of I131 was confirmed by a reduction in the urinary excretion of I131 in the 0–8 hour period. There was no significant change in the 24–hour thyroidal I131 uptake. In 2 subjects with normal thyroid function, TSH produced a threefold increase in the clearance rate. It is concluded that the thyrotoxic gland responds to TSH qualitatively in the same way as the normal trryroid gland. The significance of this finding in relation to the etiology of thyrotoxicosis is discussed.

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