Abstract
Although blood thyroid hormone levels are useful for detection of antithyroid chemicals, they are highly variable depending on blood sampling conditions. Our recent studies showed that in rats treated with thyroid peroxidase inhibitors, iodide uptake inhibitors, and thyroid hormone metabolism promotors for 28 days, histopathological and immunohistochemical analyses can be more efficient indicators than blood hormone levels. Here, six-week-old SD rats (5 males/group) were treated with inhibitors of thyroid hormone deiodination, iopanoic acid (IOP) at doses of 30 to 300 mg/kg by gavage and 0.06 to 4% erythrosine (ER) in diet, for 28 days. In the IOP groups, significant increases in serum T4 and TSH from 30 mg/kg group, serum T3 in 300 mg/kg group, and thyroid weight from 100 mg/kg group were detected. Hypertrophy of thyroid follicular cells was observed from 30 mg/kg group. Immunohistochemistry revealed an increase in TSH+ area in the anterior pituitary gland from 100 mg/kg group. In the ER groups, hypertrophy of thyroid follicular cells was found from 0.25% group, whereas there were no significant changes in serum T3/T4 levels. Thus, histopathological findings in the thyroid were detectable at same (IOP) or lower (ER) doses than those with significant changes in serum hormone levels, consistent with the results of our previous studies, suggesting that they can be more sensitive parameters for detecting antithyroid chemicals. In the IOP groups, pituitary TSH+ area increased with changes in serum TSH levels, and was considered available for evaluation of antithyroid effects.
