The activity of antioxidant enzymes and the content of uncoupling protein-1 in the brown adipose tissue of hypothyroid rats: Comparison with effects of iopanoic acid

The activity of antioxidant enzymes, copper-zinc superoxide dismutase (CuZn SOD), manganese superoxide dismutase (MnSOD) and catalase (CAT), as well as that of the mitochondrial FAD-dependent alpha -glycerophosphate dehydrogen ase (alpha -GPD) in the rat interscapular brown adipose tissue (IBAT) were studied after the treatment with methimazole (MMI) for three weeks or with iopanoic acid (IOP) for five days. Besides, the mitochondrial concentration of uncoupling protein-1 (UCP-1) and the activity of catecholamine degradin g enzyme monoamine oxidase (MAO) in the IBAT as well as the activity of the catecholamine synthesizing enzyme, dopamine beta -hydroxylase (DBH) in rat serum were examined. Judging by the significantly enhanced level of serum DBH, which is an index of sympathetic activity, and that of IBAT MAO, the i ncrease in MnSOD and CAT activities in the IBAT of hypothyroid (MMI-treated ) rats seems to be due to elevated activity of sympathetic nervous system ( SNS). However, CuZnSOD activity is not affected by SNS. On the contrary, IO P, which is a potent inhibitor of T-4 deiodination into T-3 producing "loca l" hypothyroidism, did not change either SNS activity or activities of IBAT antioxidant enzyme. However, both treatments significantly decreased IBAT UCP-1 content and alpha -GPD activity suggesting that the optimal T-3 conce ntration in the IBAT is necessary for maintaining basal levels of these key mitochondrial parameters.