Relationship between tissue respiration and total metabolic rate in hypo- and normothermic rats

¹ Max C. Fleischmann Laboratories of the Medical Sciences, School of Medicine, Stanford University, Stanford, California

The metabolic rate of whole rats was determined at body temperatures of 38 and 18 C. Rats in one series were cooled without anesthesia by the method of Giaja; those in another series were cooled during light pentobarbital anesthesia. The mean metabolic rate of rats in both series at a body temperature of 18 C was about 25% that at 38 C. Rates of O₂ consumption (Qo₂) of skeletal muscle, skin, liver, kidney, and brain were determined in Krebs medium III at 38 and at 18 C. The sum of the rates of respiration of these organs was then obtained at both temperatures and is equal to the sum of the product of tissue Qo₂ and organ weight. At 38 C the O₂ consumption of these organs is 72.5% of the metabolic rate of the whole animal at that temperature, while at 18 C the sum of the organ respiration is 106% of the metabolic rate of the whole animal at that temperature. This may be accounted for by a decrease in the mass of metabolically active tissue during hypothermia and by a low temperature coefficient for the respiration of muscle.

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