Relationship between Induction of the Phase I Enzyme System and Oxidative Stress: Relevance for Lake Trout from Lake Ontario and Early Mortality Syndrome of their Offspring
V. P. Palace, S. B. Brown, C. L. Baron, J. D. Fitzsimons, and J. F. Klaverkamp
Abstract.—By exposing lake trout Salvelinus namaycush and lake sturgeon Acipenser fulvescens to planar organochlorines in the laboratory, we have revealed a relationship between induction of the Phase I or mixed function oxidase enzyme system and oxidative stress. Indices of oxidative stress in fish exposed to organochlorines include depleted tissue stores of antioxidant vitamins and elevated concentrations of membrane breakdown products. Given the historically different organochlorine contaminant concentrations in lake trout from Lakes Ontario and Superior, an examination of Phase I induction and oxidative stress in these populations was warranted. Lake trout from Lake Ontario had greater hepatic and renal Phase I activity and lower concentrations of the antioxidant vitamin tocopherol than lake trout from Lake Superior. Lipid hydroperoxide concentrations, a measure of oxidative membrane breakdown and general oxidative stress, were also significantly higher in liver of lake trout from Lake Ontario. The relationship between oxidative stress in adult lake trout from Lake Ontario and early mortality syndrome (EMS) of their offspring was also examined. The elevated oxidative stress indices found in adult female lake trout from Lake Ontario were not correlated with the appearance of EMS in their offspring. Concentrations of antioxidant vitamins in embryos and depletion of these vitamins throughout development also did not differ between embryos with EMS and those without EMS. Eggs that later developed EMS were initially lighter in color and had lower total carotenoid concentrations. Additional work concerning the relationships of the various proretinoid forms with EMS is required. Although lake trout from Lake Ontario exhibit some oxidative stress responses, EMS among their offspring does not appear to be directly related to oxidative stress or the depletion of antioxidant vitamins.