MECHANISM OF THE THYROID STIMULATION PRODUCED BY SODIUM CHLORIDE IN THE MOUSE1

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Abstract
The mechanism by which prolonged ingestion of sodium chloride induces a stimulation of the thyroid in mice has been investigated Mice fed for 2 months on a low iodine diet containing 1% sodium chloride exhibited larger thyroid glands with a smaller iodine content than control mice fed the same diet without sodium chloride. Furthermore, radioiodine measurements performed at intervals revealed that the presence of sodium chloride in the diet increased the fraction of the body iodide excreted into the urine and decreased the fraction taken up by the thyroid. In mice given radioiodine and receiving a single intragastric dose of 30 mg sodium chloride, the amount of radioiodine excreted in the urine within the next 2-3 hours was augmented 10-20 times, while the radioiodine level in blood was lowered moderately. (Similar effects were observed in thyroidectomized but not in nephrectomized mice). Twenty-four hours after sodium chloride administration, the radioiodine content of the thyroid decreased to one half the amount in controls. These results indicated that sodium chloride increases the urinary loss of iodine and thus lowers the plasma level of this element. As a result, less iodine is available to the thyroid gland and less thyroid hormone is secreted. The pituitary gland responds by releasing more thyrotrophic hormone and thus stimulates the thyroid gland.