Seasonal variation in the antioxidant defense system of the brain of the ground squirrel (Citellus citellus) and response to low temperature compared with rat.

Seasonal variation in the activity of antioxidant enzymes (superoxide dismutase (EC 1.15.1.1.; SOD), catalase (EC 1.11.1.6; CAT), glutathione peroxidase (EC 1.11.1.9; GSH-Px), glutathione reductase (EC 1.6.4.2; GR), glutathione-S-transferase (EC 2.5.1.18; GST) and low-molecular-weight antioxidants: ascorbic acid (AsA), vitamin E (VIT E) and glutathione (CSH+GSSG) were examined in the brain of the ground squirrels (Citellus citellus) maintained at 30 degrees C during the whole year. The highest activity (per mg protein) of antioxidant defense (AD) enzymes was found in the spring and was much lower in the summer. A further decrease in activity of CAT, GSH-Px and GST was observed in the winter. The highest levels of AsA and glutathione were recorded in winter in comparison with spring and summer. AD system in the brain of the ground squirrel and rates (maintained at thermoneutrality) exposed to low temperature (4 degrees C) for 3, 6 or 24 hr during the summer was studied as well. Summer was chosen as a period of stable euthermia for ground squirrels and in thermoregulation similar to rats. Consumption of free fatty acid and glucose during the acute exposure to low temperature was found to be species specific. In the ground squirrel, an increase in the specific activities of SOD, after 3, 6 and 24 hr, CAT after 3 and 6 hr and GR after 6 hr of exposure to low temperature was detected. When activities were expressed in U/g wet mass, an increase of SOD after 3, 6 and 24 hr (P < 0.02, P < 0.02, P < 0.005) and CAT and GSH-Px 3 hr (P < 0.01) upon exposure to low temperature was observed. In the rats, no changes in the specific activities of these enzymes after exposure to low temperature were recorded and only an increase in GST activity (U/g wet mass) after 6 hr exposure was registered. Low-molecular-weight AD components in both animal species were unchanged upon short-term exposure to low temperature. The species-specific differences in brain AD between the rats and the ground squirrels after short exposure to low temperature may be ascribed to seasonal changes of the brain activity in the latter.