T6 AM Environmental Hypoxia
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 324-326

(COO-1117-814922) Antioxidant enzyme response to hypoxia-induced oxidative stress in the estuarine fish Leiostomus xanthurus.

Cooper, R¹, Clough, L¹, Farwell, M¹, West, T¹, ¹ East Carolina University, Greenville, NC, USA

ABSTRACT- The objective of this research was to examine the physiological impact of hypoxia on antioxidant enzyme activity levels in the estuarine fish Leiostomus xanthurus (spot). The research was conducted in three parts: 1) an examination of the response of antioxidant enzymes to varying degrees of hypoxia; 2) an examination of the response of antioxidant enzymes to hypoxic preconditioning, periods of sub-lethal hypoxic exposure followed by reoxygenation; and 3) an examination of the response of antioxidant enzymes to a subsequent hypoxic challenge after hypoxic preconditioning. The antioxidant enzymes assayed included superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). In response to varying degrees of oxygen saturation, SOD activity levels increased after 12 hours of exposure to 10% (0.8 mg/L) relative to 50% (4.0 mg/L) oxygen saturation. A single, variable duration exposure to hypoxic preconditioning was shown to increase activity levels of SOD and decrease activity levels of CAT immediately following exposure. Activity levels continued to steadily change over the normoxic recovery period, with the degree of change roughly proportional to the duration of the hypoxic preconditioning. Hypoxic preconditioning, applied using a cyclic protocol, did not have an immediate impact on activity levels of the antioxidant enzymes. When preconditioned fish were subsequently exposed to a hypoxic challenge, 12 of the 16 significant comparisons (75%) resulted in preconditioned fish showing reduced activity levels when compared to non-preconditioned fish. This suggests that hypoxic preconditioning in spot does not protect against subsequent hypoxic exposure by increasing activity of the antioxidant enzymes as reported with other organisms. Finally, high levels of inter-individual variation in activity levels were observed in these fish. This variation does not appear to be linked to prior exposure history; instead it likely reflects variable genetic expression between individuals.

Key words: hypoxia, antioxidant enzymes, estuarine fish