The effect of iodine on lipid peroxidation and ultrastructure in the thyroids of BB/Wor rats.

There has been recent data suggesting that iodine potentiates lymphocytic thyroiditis (LT) by inciting oxidative stress. However, the mechanism by which iodine induces LT in genetically predisposed animals is unknown. This study was undertaken to examine LT-prone BB/Wor (LT-P) rat thyroids for signs of acute iodine toxicity and oxidative damage before the onset of spontaneous LT. Lipid peroxidation was assessed by the measurement of malonyldialdehyde (MDA) in thyroid homogenates after randomization to a treatment group receiving 0.05% iodide in the drinking water or tap water for 24 hours. Basal MDA levels were higher in LT-prone rat thyroids than Wistar rat thyroids, but iodine treatment did not influence intrathyroidal MDA levels. Electronmicroscopy demonstrated that prolonged treatment with excess iodine, increased the number of apical lysosomes. But there were no ultrastructural changes unique to LT-P rat thyroids. These data suggest that although LT-P rat thyroids may experience subclinical oxidative damage before the onset of histologically demonstrable LT, this activity is not affected by iodine.