Thyroid Function in a Goiter Endemic. V. Mechanism of Thyroid Failure in the Uele Endemic Cretins

Abstract

Iodine metabolism has been investigated in 35 hypothyroid endemic cretins in the Uele (Congo). The salivary excretion of iodide, the potassium thiocyanate (KSCN) thyroid discharge test and the chromatographies of I¹³¹ iodoamino acids of the plasma were normal. The DIT excretion test, and the BEI¹³¹ /PBI¹³¹ ratios excluded major defects in iodotyrosine deiodination and in thyroglobulinolysis. In one cretin only was a metabolic block observed. Indices of the iodide uptake (thyroid clearance rate, total disposal rate, radioiodide uptake and absolute iodine uptake by the thyroid) were all markedly low when compared to the same indices in well-developed adults of the same area. Thyroid hormone secretion proceeded at a very fast rate, but involved only minute amounts of I¹²⁷. It is concluded that the thyroidal exchangeable pool of organic iodine is very small in these patients. Evidence is presented that this pool is not homogeneous. Thyroid metabolism appears unaffected by TSH stimulation or by a mild suppression by T3. The thyroids in endemic cretins are already functioning at their highest level of activity. It is concluded that the fundamental defect of the thyroid in the Uele endemic cretins is its failure to grow and to increase its iodide uptake efficiency in response to hypothyroidism and iodide deficiency.