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First published online February 15, 2006
Journal of Experimental Biology 209, 817-825 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02045

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Differential effects of experimental and cold-induced hyperthyroidism on factors inducing rat liver oxidative damage

P. Venditti^1,*, R. Pamplona², V. Ayala², R. De Rosa¹, G. Caldarone¹ and S. Di Meo¹

¹ Dipartimento delle Scienze Biologiche, Sezione di Fisiologia, Università di Napoli, I-80134 Napoli, Italy
² Departament de Ciènces Mèdiques Bàsiques, Universitat de Lleida, 25198 Lleida, Spain

^* Author for correspondence (e-mail: venditti{at}unina.it)

Accepted 19 December 2005

Thyroid hormone-induced increase in metabolic rates is often associated with increased oxidative stress. The aim of the present study was to investigate the contribution of iodothyronines to liver oxidative stress in the functional hyperthyroidism elicited by cold, using as models cold-exposed and 3,5,3'-triiodothyronine (T₃)- or thyroxine (T₄)-treated rats. The hyperthyroid state was always associated with increases in both oxidative capacity and oxidative damage of the tissue. The most extensive damage to lipids and proteins was found in T₃-treated and cold-exposed rats, respectively. Increase in oxygen reactive species released by mitochondria and microsomes was found to contribute to tissue oxidative damage, whereas the determination of single antioxidants did not provide information about the possible contribution of a reduced effectiveness of the antioxidant defence system. Indeed, liver oxidative damage in hyperthyroid rats was scarcely related to levels of the liposoluble antioxidants and activities of antioxidant enzymes. Conversely, other biochemical changes, such as the degree of fatty acid unsaturation and hemoprotein content, appeared to predispose hepatic tissue to oxidative damage associated with oxidative challenge elicited by hyperthyroid state.

As a whole, our results confirm the idea that T₃ plays a key role in metabolic changes and oxidative damage found in cold liver. However, only data concerning changes in glutathione peroxidase activity and mitochondrial protein content favour the idea that dissimilarities in effects of cold exposure and T₃ treatment could depend on differences in serum levels of T₄.

Key words: cold exposure, antioxidant capacity, free radical, lipid peroxidation, protein carbonyl

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