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.