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First published online July 20, 2006
Journal of Experimental Biology 209, 2893-2901 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02320

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Effects of hypo- and hyperoxia on transcription levels of five stress genes and the glutathione system in liver of Atlantic cod Gadus morhua

P. A. Olsvik^1,*, T. Kristensen², R. Waagbø¹, K.-E. Tollefsen², B. O. Rosseland³ and H. Toften⁴

¹ National Institute of Nutrition and Seafood Research, N-5817 Bergen, Norway
² Norwegian Institute for Water Research, N-0411 Oslo, Norway
³ Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, N-1432 Aas, Norway
⁴ Fiskeriforskning, N-9291 Tromsø, Norway

^* Author for correspondence (e-mail: pal.olsvik{at}nifes.no)

Accepted 10 May 2006

The transcript levels of three genes coding for antioxidants, Cu/Zn superoxide dismutase (SOD), catalase and phospholipid hydroperoxide glutathione peroxidase (GSH-Px), and those of two stress proteins, metallothionein (MT) and CYP1A, were examined with real-time quantitative (q) RT-PCR in hepatic tissue of Atlantic cod exposed to 46% (hypoxia), 76% (normoxia) and 145% (hyperoxia) O₂ saturation (tank outlet). To evaluate the oxidative stress state, the levels of total glutathione (tGSH), reduced glutathione (GSH) and oxidized glutathione (GSSG) and subsequently the oxidative stress index (OSI), were determined in the same tissue samples. The transcript level of GSH-Px was significantly upregulated in fish exposed to hyperoxia, and significantly downregulated in fish exposed to hypoxia, compared to the normoxia group. Significant downregulation was also found for SOD and CYP1A transcriptional levels in fish exposed to hypoxia. The transcript levels of catalase and MT did not change in liver of cod exposed to suboptimal oxygen levels. No significant differences were seen between the groups for tGSH, GSH, GSSG or OSI. Prolonged exposure to unfavourable oxygen saturation levels did not alter the OSI, indicating that the antioxidant glutathione system is maintained at an unchanged level in liver of the examined cod.

Key words: Atlantic cod, hyperoxia, hypoxia, oxidative stress, gene expression, oxidative stress index, glutathione