Changes in thyroidal function and liver UDPglucuronosyltransferase activity in rats following administration of a...

SC-37211, an imidazole with antianaerobic activity, was administered po to male rats for 2 weeks at dosages of 20, 60, and 200 mg/kg/day. Histological changes in the thyroid included irregularly shaped follicles and slightly enlarged follicular cells. Serum triiodothyronine (T3) and/or thyroxine (T4) were significantly decreased in treated animals at all dosages; these decreases were not observed following a 2-week recovery period. The half-life of serum [125I]thyroxine was also significantly decreased in rats treated with SC-37211. Morphological changes in the thyroid are likely the result of thyroid-stimulating hormone (TSH) stimulation, a response to decreased serum T3 and T4 concentrations. The decreases in T3 and T4 were not due to decreases in iodide uptake or organification. There were dose-dependent increases in liver weights, liver-to-body weight ratios, and UDPglucuronosyltransferase activity toward p-nitrophenol and T4. Therefore, the decreases in serum T3 and T4 were probably due to an increase in hepatic metabolism rather than to a direct effect of SC-37211 on the thyroid.