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1 Department of Biology,
Philipps-University, D-35032 Marburg, Germany;
2 Nutrition Research Division,
Djungarian hamsters (Phodopus
sungorus) acclimated to a short photoperiod (8:16-h
light-dark cycle) display spontaneous daily torpor with ad libitum food
availability. The time course of body temperature
(Tb), metabolic rate,
respiratory quotient (RQ), and substrate and enzyme changes was
measured during entrance into torpor and in deep torpor. RQ, blood
glucose, and serum lipids are high during the first hours of torpor but
then gradually decline, suggesting that glucose is the primary fuel
during the first hours of torpor, with a gradual change to lipid
utilization. No major changes in enzyme activities were observed during
torpor except for inactivation of the pyruvate dehydrogenase (PDH)
complex in liver, brown adipose tissue, and heart muscle. PDH
inactivation closely correlates with the reduction of total metabolic
rate, whereas in brain, kidney, diaphragm, and skeletal muscle, PDH activity was maintained at the initial level. These findings suggest inhibition of carbohydrate oxidation in heart, brown adipose tissue, and liver during entrance into daily torpor.
Phodopus sungorus; body temperature; metabolic rate; metabolic inhibition; enzymes
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