Modulation of rat liver mitochondrial antioxidant defence system by thyroid hormone

In the present study the effect of thyroid hormone (T-3) on oxidative stres s parameters of mitochondria of rat liver is reported. Hypothyroidism is in duced in male adult rats by giving 0.05% propylthiouracil (PTU) in drinking water for 30 days and in order to know the effect of thyroid hormone, PTU- treated rats were injected with 20 mug T-3/100 g body weight/day for 3 days . The results of the present study indicate that administration of T-3 to h ypothyroid (PTU-treated) rats resulted in significant augmentation of oxida tive stress parameters such as thiobarbituric acid reactive substances and protein carbonyl content of mitochondria in comparison to its control and e uthyroid rats. The hydrogen peroxide content of the mitochondria of liver i ncreased in hypothyroid rats and was brought to a normal level by T-3 treat ment. Induction of hypothyroidism by PTU treatment to rats also resulted in the augmentation of total and CN-sensitive superoxide dismutase (SOD) acti vities of the mitochondria, which was reduced when hypothyroid rats were ch allenged with T-3. Although CN-resistant SOD activity of the mitochondria r emained unaltered in response to hypothyroidism induced by PTU treatment, i ts activity decreased when hypothyroid rats were injected with T-3. The cat alase activity of the mitochondria decreased significantly by PTU treatment and was restored to normal when PTU-treated rats were given T-3. Total, Se -independent and Se-dependent glutathione peroxidase activities of the mito chondria were increased following PTU treatment and reduced when T-3 was ad ministered to PTU-treated rats. The reduced and oxidised glutathione conten ts of the mitochondria of liver increased significantly in hypothyroid rats and their level was restored to normal when hypothyroid rats were injected with T-3. The results of the present study suggest that the mitochondrial antioxidant defence system is considerably influenced by the thyroid states of the body. (C) 2001 Elsevier Science B.V. All rights reserved.