Antithyroid Effects of 3-Amino-1,2,4-triazole ∗

Summary

The effects of 3-amino-1,2,-4-triazole (ATZ) on weight, content of iodine, and histology of the thyroid in rats were determined and compared to the effects of propylthiouracil (PTU), and KCIO₄. In an 83-day period of treatment, ATZ and PTU produced goiters of comparable size. The KCIO₄ treatment resulted in slightly greater depletion of iodine in the thyroid, smaller goiters, and less thyroxine depletion of the thyroid. The effect of ATZ treatment on intrathyroid metabolism of iodine in rats was studied and compared to similar studies in rats without treatment. In the ATZ-treated group, there was a progressive decrease in T3 and T4 and a slight increase in the proportion of MIT. The biologic half-life of ¹³¹I in the thyroid of the control and treated groups was 4.9 and 1.3 days, respectively. These findings are similar to those found previously for PTU and show that ATZ, like PTU, not only interferes with organification of iodine but also inhibits the coupling of iodotyrosines to form iodothyronines.