Up-regulation of an extracellular superoxide dismutase-like activity in hibernating hamsters subjected to oxidative stress in mid- to late arousal from torpor

Torpor–arousal cycles, one of the inherent features in hibernators, are associated with a rapid increase in body temperature and respiration, and it would lead to elevation of reactive oxygen species (ROS) generation. However, hibernators apparently tolerate this oxidative stress. We have observed in Syrian hamsters (Mesocricetus auratus) a maximal temperature shift and respiratory rate in mid- to late arousal (16–33 °C rectal temperature) from torpor. To examine plasma antioxidant status during arousal, we studied total superoxide radical-scavenging activity in plasma by electron spin resonance. The superoxide radical-scavenging activity reached a maximum at 32 °C, coincident with a peak in plasma uric acid levels, a ROS generation indicator. The up-regulated activity at 32 °C was attributable to the peak of the activity eluted at 260-kDa on gel-filtration chromatography, but was not to small antioxidant molecules such as ascorbate and α-tocopherol. The activity eluted at 260-kDa increased 3-fold at 32 °C compared with that of the torpid state, and was not detected either at 6 h after the onset of arousal or in the euthermic state. Moreover, the activity exhibited extracellular SOD-like properties: its induction in plasma by heparin injection and its affinity for heparin. Our results suggest that the 260-kDa extracellular SOD-like activity plays a role in the tolerance for the oxidative stress during arousal from torpor.