Metabolic adjustments during daily torpor in the Djungarian hamster

Djungarian hamsters (Phodopus sungorus) acclimated to a short photoperiod ( 8:16-h light-dark cycle) display spontaneous daily torpor with ad libitum f ood availability. The time course of body temperature (T-b), metabolic rate , respiratory quotient (RQ), and substrate and enzyme changes was measured during entrance into torpor and in deep torpor. RQ, blood glucose, and seru m Lipids are high during the first hours of torpor but then gradually decli ne, suggesting that glucose is the primary fuel during the first hours of t orpor, with a gradual change to lipid utilization. No major changes in enzy me activities were observed during torpor except for inactivation of the py ruvate dehydrogenase (PDH) complex in Liver, brown adipose tissue, and hear t muscle. PDH inactivation closely correlates with the reduction of total m etabolic rate, whereas in brain, kidney, diaphragm, and skeletal muscle, PD H activity was maintained at the initial level. These findings suggest inhi bition of carbohydrate oxidation in heart, brown adipose tissue, and liver during entrance into daily torpor.