BIOCHEMISTRY OF BROWN FAT AND LIVER OF HIBERNATING GOLDEN-MANTLED GROUND SQUIRRELS (CITELLUS LATERALIS)

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Abstract
Studies were made on the effects of cold acclimation culminating in hibernation on the weight and mitochondrial nitrogen content and enzymatic activity of brown fat and liver of ground squirrels (Citellus lateralis). The hibernating animals were living at a room temperature of 2 ± 1 °C, the controls at 24 ± 2 °C. The body and liver weights of the hibernating animals were both 20% lower than those of the controls, but the brown fat of the hibernators was 40% greater in absolute weight and its ratio to body weight was double that of the controls. Respiration rates of liver and interscapular brown fat mitochondria from both control and hibernating squirrels were determined with various substrates. Oxidation of α-glycerophosphate and glutamate by brown fat mitochondria from hibernating animals was 47% and 36% higher, respectively, than control values. Liver mitochondria from hibernating animals were 50% higher in oxidation of succinate than were control mitochondria, but 34% lower in oxidation of α-glycerophosphate. The increased oxidative activity of brown fat, together with the increased ratio of brown fat weight to body weight, indicates that the thermogenic capability of brown fat is enhanced in the process of preparation for hibernation.