Glucose, glycogen, and insulin responses in the hypothermic rat

The rat appears to be unable to utilize glucose during hypothermia. The objective of this study was to examine carbohydrate homeostasis during induction, hypothermia, and rewarming phases. Groups of normothermic animals were euthanized to serve as time controls for comparison. Hypothermia (15 degrees C) was produced by exposure to helox (80% helium:20% oxygen) at 0 +/- 1 degree C. Hyperglycemia was noted during the induction process (169 +/- 8 in control vs 326 +/- 49 mg/dl). Serum glucose increased further during 4 hr of hypothermia, but following rewarming (Tre of 33 +/- 1 degrees C) was reduced (153 +/- 16 mg/dl) significantly (P less than 0.05). Serum insulin was depressed during hypothermic induction (from 48 +/- 4 in controls to 19 +/- 3 microU/ml in hypothermic rats) and increased only slightly during the arousal process, remaining significantly lower than in normothermic subjects. Initial hepatic, skeletal muscle, and cardiac glycogen concentrations were reduced 34, 68, and 75%, respectively, during hypothermic induction. While liver glycogen decreased further during 4 hr of hypothermia, skeletal and cardiac stores increased markedly. During rewarming, hepatic glycogen was markedly decreased, while skeletal and cardiac stores were maintained. These data suggest that hyperglycemia in the hypothermic rat can be accounted for by glycogenolysis and hypoinsulinemia. In addition, this study indicates repletion of skeletal and cardiac muscle glycogen during maintained hypothermia and sparing of muscle glycogen during rewarming.