Relation Between Thyroid Iodine Content and the Accumulation and Oxidation of [35S]Methimazole in the Rat

The thyroid accumulation and oxidation of a single intraperitoneal dose of [35S]methimazole has been studied in iodine-deficient, normal and iodine-treated rats. A highly significant positive linear correlation was found between the thyroid oxidation of methimazole to sulfate and intrathyroidal iodine content. A single dose of potassium iodide given intraperitoneally (ip) to rats. 1 h before administration of [35S]methimazole (1 mg/kg ip) increased the thyroid accumulation and oxidation of methimazole. Conversely, the thyroids of rats maintained on a low iodine diet for 21 days showed a markedly reduced capacity to accumulate and oxidize methimazole. The level of oxidation found in the iodinedeficient, normal and iodide-treated groups was 0.21,4.15 and 12.6 nmol sulfate/g thyroid respectively. The animals maintained on the low iodinediet for 21 days showed significant increases in thyroid weight and thus the decrease in methimazole oxidation occurred in spite of increased stimulation by endogenous TSH. Th...