Glutathione systems and anoxia tolerance in turtles

Effects of anoxic submergence (20 h at 5 degrees C) and subsequent 24 h aerobic recovery on glutathione levels and the activities of glutathione-related enzymes were examined in six tissues of Trachemys scripta elegans. Anoxia exposure resulted in tissue-specific changes in enzyme maximal activities, the most dramatic being suppression of gamma-glutamyl transpeptidase (gamma-GTPase) activity in anoxic kidney to only 2% of control. Anoxia exposure also caused significant decreases in activities of liver and heart glutathione-S-transferase (GST) (by 25 and 42%), heart glutathione reductase (GR) (by 67%), liver gamma-GTPase (by 71%), and red muscle glutaredoxin (GRN) (by 56%). By contrast, anoxia exposure increased the activities of GR in liver and red muscle (by 52 and 80%), glutathione synthetase (GS) in white muscle (by 300%), and GRN in white muscle (by 400%). During aerobic recovery after anoxia, GST activity decreased in red muscle, kidney, and brain (by 72, 56, and 39%); GR decreased in liver and red muscle (by 52 and 80%); and GRN fell in red muscle (by 56%). Other activities rose during recovery: GR in heart (by 64%), GS in heart and brain (by 200%), and gamma-GTPase in brain (by 63%). Tissue pools of total glutathione were high in comparison with other ectotherms. Levels decreased during anoxia in four organs to 49-67% of control values. During aerobic recovery the reduced glutathione-to-oxidized glutathione ratio (GSH/GSSG) increased in heart, kidney, and brain, indicating that oxidative stress did not occur in these organs. Rather than maintaining high levels of glutathione in tissues to prevent oxidative stress during aerobic recovery, turtles sustain high GSH/GSSG by regulating the activities of glutathione-using enzymes.