Arousal from Torpor Increases Oxidative Damage in the Hibernating Thirteen-Lined Ground Squirrel (Ictidomys tridecemlineatus)

During hibernation, especially during arousal from torpor to interbout euthermia (IBE), blood flow changes drastically. In nonhibernating mammals, similar changes during ischemia/reperfusion lead to oxidative damage. We hypothesized that suppression of mitochondrial metabolism during hibernation protects against such damage. We compared markers of oxidative damage and total antioxidant capacity in eight tissues among summer, torpid, and IBE thirteen-lined ground squirrels. Overall, summer tissue had less lipid and protein oxidative damage than tissue from the hibernation season, but DNA damage (in four tissues) and total antioxidant capacity (in all eight tissues) were similar among all groups. During torpor, when mitochondrial metabolism is suppressed, lipid damage in heart, brown adipose tissue, and small intestine was lower than IBE by as much as fivefold. By contrast, oxidative damage to protein was at least twofold higher in liver and skeletal muscle in torpor compared with IBE. Our findings suggest that arousal from torpor creates oxidative damage similar to ischemia/reperfusion injury but that this damage is repaired during IBE. These differences cannot be explained by changes in antioxidant capacity, so they are likely due to differences is reactive oxygen species production among hibernation states that may relate to the well-characterized reversible suppression of mitochondrial metabolism during torpor.