THE EFFECTS OF CERTAIN ANTITHYROID DRUGS ON THE UPTAKE OF RADIOACTIVE IODINE BY THE FROG THYROID

¹ Department of Biology, The Catholic University of America, Washington, D. C.

1. The iodine-concentration capacity of the thyroid gland, as measured by the uptake of radioactive iodine, was depressed in frogs injected with thiourea, sulfanilamide and potassium thiocyanate. The subcutaneous injection of 0.5 cc. of a 10 per cent solution of thiourea and of sulfanilamide, and 1 cc. of a 0.2 per cent solution of potassium thiocyanate into normal frogs resulted in an enlarged, hyperemic and hyperplastic thyroid gland. The thyroid hyperplasia which occurred under the influence of these drugs was a secondary compensatory response to the increased thyrotropic hormone output by the hypophysis. Inhibition was most pronounced with thiourea, sulfanilamide and potassium thiocyanate following in that order.

2. Injected potassium thiocyanate was rapidly removed from the blood stream, and its elimination was practically complete in 24 hours. However, the iodine-concentrating capacity of the thyroid gland, as measured by the uptake of radioactive iodine, was depressed by potassium thiocyanate, provided a high concentration of the drug was still present in the circulation. After 24 hours, the enlarged thyroids of the potassium thiocyanate-treated frogs had a greater capacity than normal for absorbing injected radioactive iodine.