Thyroid function in rats administered excess iodide.

ABSTRACT The effects of excess iodide on the histology and function of the thyroid were studied in rats. A slight increase in thyroid weight and minimal histological alterations were observed. The thyroid function of rats was studied by measuring the serum total and free thyroxine. Excess iodide did not significantly change the concentration of thyroid hormone in the serum and signs of hypothyroidism were not seen. Thus, rats were capable of adaptation to chronic administration of large amounts of iodide. A slight increase in the serum thyrotrophin after prolonged ingestion of excess iodide was measured with both bioassay and radioimmunoassay techniques. The possible role of thyrotrophin in the mechanism of escape from the transient inhibition of iodide on thyroid hormone synthesis is discussed.