Effect of Dietary Iodine on Autoimmune Thyroiditis in the BB Wistar Rat

Diabetes-prone BB Wistar rats were fed a modified AIN-76 diet providing the following amounts of iodine for 10 wk: 0.2 mg/kg diet (recommended amount); 1.0 mg/kg; 2.0 mg/kg; or 3.0 mg/kg. The thyroids were examined for gross and microscopic changes and sera were assayed for antibodies to triiodothyronine (T3), thyroxine (T4), and thyroglobulin (Tg). The body weights and food consumption of the rats fed 0.2 mg of iodine/kg were significantly lower than those of the animals fed higher amounts. Urinary iodine excretion reflected dietary intakes. The thyroids from animals fed 2.0 and 3.0 mg/kg were significantly (P less than 0.01) larger than those from animals fed 0.2 mg/kg. One rat fed 0.2 mg/kg and 2 rats in each group fed 2.0 and 3.0 mg/kg had extensive lymphocytic thyroiditis. Three rats fed 1.0 mg/kg, 6 fed 2.0 mg/kg and 6 fed 3.0 mg/kg had enlarged thyroids. Two rats fed 0.2 mg/kg, 2 fed 2.0 mg/kg and 6 fed 3.0 mg/kg had detectable Tg antibodies. These data suggest that high iodine intakes increase Tg antibodies, which may be associated with an increase in autoimmune thyroiditis in these animals.