THE IODIDE CONCENTRATING MECHANISM OF THE RAT THYROID AND ITS INHIBITION BY THIOCYANATE1

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Abstract
The observation is confirmed that thyroid depleted of hormonal iodine under the influence of propyl-thiouracil is still capable of concentrating large quantities of iodine when K iodide is injd. This iodine is held in the reduced form as iodide under these conditions. It is entirely ultrafiltrable and all has been shown to be iodide when titrated potentiometrically using a silver-silver iodide electrode. A gradient exists between serum and thyroid iodide conc. This gradient is decreased only when the serum iodide level is relatively high. The thyroid serum-iodide gradient increases in the range of 10-fold with thyroid hyperplasia, induced by propylthiouracil. The thyroid may hypertrophy to 3 or more times normal size concomitantly with hyperplasia. This results in a total ability of the stimulated thyroid to accumulate an amt. of iodide 30 or more times greater than the amt. concentrated by a normal gland in equilibrium with a similar serum iodide conc. Thiocyanate inhibits preferential conc. of iodide by thyroid tissue. It causes discharge of iodide from the thyroid as well as preventing its uptake. Thiocyanate in the dosage tested still has a partial inhibitory effect on thyroid iodide conc. 5 hrs. after injn. Bromide ion in doses over 500 times that of injd. iodide will not cause significant iodide displacement from thyroid tissue. Sulfa-guanidine does not prevent iodide conc. by the thyroid.