THE EFFECT OF CERTAIN GOITROGENIC DRUGS ON THE ABSORPTION OF RADIOACTIVE IODINE BY THE THYROID GLAND

II. Collection of Raldioiodine by Thyroids of Rats and Chicks Following a Single Injection of These Agents

¹ The Research Laboratories of Parke, Davis and Company, Detroit, Michigan, The Thyroid Clinic of the Massachusetts General Hospital, Boston, Massachusetts, and the Radioactivity Center of the Massachusetts Institute of Technology, Cambridge, Massachusetts

The antithyroid action of several goitrogenic compounds was studied quantitatively by comparing the effect and duration of effect of varying doses of these agents, when injected subcutaneously, on the collection of radioiodine by the thyroids of rats and chicks.

The drugs studied included thiouracil, propylthiouracil, benzylthiouracil, methylthiouracil, 5-aminothiadiazole-2-thiol (TC-68), 3-(phenylaminomethyl)-thiazolidine-2-thione (TC-105), 2-aminothiazole and potassium thiocyanate.

In the rat, it was observed that propyl and benzylthiouracil were ten times as effective as thiouracil and methylthiouracil in inhibiting the thyroid's natural capacity to collect iodine. The duration of inhibitory action of minimal effective doses of these drugs was not materially different. In all cases at least partial escape from the drug effect occurred eight hours after administration.

In the cockerel, the minimal effective inhibitory doses of all compounds were greater than in the rat. Benzylthiouracil was observed to be approximately ten times more effective than thiouracil, propylthiouracil and TC-68. TC-105 aminothiazole and potassium thiocyanate had about one-half the activity of thiouracil. The duration of action of minimal effective doses was six hours. With the exception of aminothiazole, in all instances escape from the block to iodine collection was complete 24 hours after injection of the drug.

Certain fundamental differences between the iodine-blocking effect and the goitrogenic action of these agents are discussed.

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