The effect of hibernation status and cold-acclimation on hepatocyte gluconeogenesis in the golden-mantled ground squirrel (Spermophilus lateralis)

Abstract

Rates of gluconeogenesis were measured in hepatocytes isolated from torpid, aroused, summer-sampled non-cold-acclimated, and summer-sampled cold-acclimated Spermophilus lateralis. At 7°C, no net glucose synthesis is measurable. At 37°C, 10 mM alanine supports low rates of gluconeogenesis that do not differ among groups. With 10 mM lactate/1 mM pyruvate, rates of gluconeogenesis are 60% higher in the torpid group than in the summer non-cold-acclimated group. With 10 mM glycerol, rates of gluconeogenesis are 2-fold higher in the torpid, aroused, and summer cold-acclimated groups than in the summer non-cold-acclimated group. The higher rates of gluconeogenesis with lactate/pyruvate and glycerol are probably more related to cold-acclimation than to hibernation/seasonal status per se, as no differences were noted among the cold-exposed groups. The observed differences in rates of gluconeogenesis cannot be readily explained by differences in apparent oxidative efficiencies of gluconeogenesis or activities of key gluconeogenic enzymes, but may be related to a general upregulation of hepatocyte metabolism accompanying cold-acclimation. This is reflected in the higher rates of hepatocyte oxygen consumption in the cold-exposed groups. Increased biosynthetic capacities during the winter season may not be a specific adaptation to hibernation, but may still contribute to energy savings over the hibernation season by helping to minimize euthermic arousal intervals.