Antithyroid Action of 3-Amino-l, 2,4=triazole*

It was first shown by Heim et al. (2, 3) that 1 hour after S-amino-l ,2,4-triazolel has been injected into rats, there is a marked inhibition of liver and kidney catalase, a lesser inhibition of liver peroxidase, and no inhibition of erythrocyte catalase activity. In view of this rather selective action towards tissue hydroperosidases, it seemed possible that aminotriazole should exhibit antithyroid activity by inhibiting thyroid iodide perosidase (4, 5), if such an enzyme exists (6). In essence, the action of aminotriazole would resemble that of propylthiouracil (7), whereby the thyroid gland is prevented from forming organically bound iodine, but can still concentrate plasma iodide. This report demonstrates that aminotriazole inhibits thyroid 1131 uptake and the organic binding of radioiodine without affecting the iodide trap.