BIOTRANSFORMATION AND GLUTATHIONE HOMEOSTASIS IN RAINBOW-TROUT EXPOSED TO CHEMICAL AND PHYSICAL STRESS

Glutathione, together with biotransformation and antioxidative enzymes , plays an important role in protecting the cells against damage cause d by free radicals, peroxides, oxidizing metabolites and xenobiotics i ntroduced by environmental stress. Pollution of the environment causes many long-term physiological effects on fish. Furthermore, in mammals exercise increases oxidative stress (increase of reactive oxygen spec ies) which overloads the defence mechanisms. Induction of the glutathi one system could show whether physical stress also affects defence mec hanisms of fish. In the present series of studies we have investigated the biotransformation and glutathione homeostasis of rainbow trout ex posed to chemical and physical stress. Juvenile rainbow trout (Oncorhy nchus mykiss) were exposed to water-borne hexachlorobenzene (HCB; 2 mu g/litre) together with duck-weed (Lemna minor) using different combin ations of fish, plants and HCB. In another experiment, fish were held in different water flows (none, medium, high). Hepatic monooxygenase ( EROD) and conjugation (GST) enzyme activities, as well as antioxidant systems (GPX, GR, tGSH) were measured. in the HCB-exposed fish-plant g roup EROD activities in fish were suppressed compared with the unconta minated group. It is probable that through digested plants the fish co uld have been exposed to possible plant-derived HCB metabolites or sec ondary metabolites. Fish of different physical activity showed slightl y elevated EROD activities three weeks from the beginning of the exper iment. After the following three-week period EROD activities had decre ased to the starting level. Three weeks from the beginning GST activit ies were at their highest level. The elevation of mono-oxygenase activ ities may, have caused increased production of reactive intermediates which were further metabolized through activated glutathione system. E levated total glutathione contents in studied tissues showed the poten cy of these fish to resist oxidative stress. Copyright (C) 1996 Elsevi er Science Ltd