ANTIOXIDANT SYSTEMS AND ANOXIA TOLERANCE IN A FRESH-WATER TURTLE TRACHEMYS-SCRIPTA ELEGANS

The effects of anoxic submergence (20 h at 5 degrees C) and subsequent 24 h aerobic recovery on the antioxidant systems of six organs were e xamined in freshwater turtles, Trachemys scripta elegans. Both xanthin e oxidase and xanthine dehydrogenase were detected in turtle tissues w ith xanthine oxidase composing 36-75% of the total activity. Turtle or gans displayed high constitutive activities of catalase (CAT), superox ide dismutase (SOD), and alkyl hydroperoxide reductase (AHR). Measurem ents of lipid peroxidation damage products (conjugated dienes, lipid h ydroperoxides, thiobarbituric acid reactive substances) showed minimal changes during anoxia or recovery suggesting that natural anoxic-aero bic transitions occur without the free radical damage that is seen dur ing ischemia-reperfusion in mammals. Anoxia exposure led to selected d ecreases in enzyme activities in organs, consistent with a reduced pot ential for oxidative damage during anoxia: SOD decreased in liver by 3 0%, CAT decreased in heart by 31%, CAT and total glutathione peroxidas e (GPOX) decreased in kidney (by 68 and 41%), and CAT and SOD decrease d in brain (by 80 and 15%). AHR, however, increased 2 and 3.5 fold dur ing anoxia in heart and kidney respectively. Most anoxia-induced chang es were reversed during aerobic recovery although brain enzyme activit ies remained suppressed. Some specific changes occurred during the rec overy period: SOD increased from controls in heart by 45%, AHR increas ed to 200 and 168% of control values in red and white muscle respectiv ely, and total GPOX decreased from controls in heart and white muscle by 75 and 77% respectively. The results show that biochemical adaptati on for natural anoxia tolerance in turtles includes well-developed ant ioxidant defenses that minimize or prevent damage by reactive oxygen s pecies during the reoxygenation of organs after anoxic submergence.