Temperature effect on oxygenation and metabolism of perfused rat hindlimb muscle

The effects of temperature on oxygenation and metabolism in perfused rat hindlimb was studied at 35 degrees C and 15 degrees C. Oxygenation of myoglobin and oxidation of cytochrome aa3 in the thigh (quadriceps) muscle were estimated from the difference spectra measured with a rapid-scanning spectrophotometer. Simultaneously, oxygen uptake and release of lactate and pyruvate were measured. (1) In hypothermia, glycolysis played a major role in energy metabolism even though Cyt aa3 was maintained in a more oxidized state than in normothermia. (2) P50 of myoglobin in perfused rat hindlimb was 5.0 mmHg at 35 degrees C, 2.3 mmHg at 25 degrees C and 1.1 mmHg at 15 degrees C. The delta H degree was -13.0 kcal/mol. (3) When about 30% of myoglobin was deoxygenated at both 35 degrees C and 15 degrees C, the oxygen uptake started to decrease and lactate release increased. (4) At 35 degrees C, the oxidation level of cytochrome aa3 was same as the oxygenation level of myoglobin. At 15 degrees C, however, the oxidation level of cytochrome aa3 was clearly higher than the oxygenation level of myoglobin. The oxygen uptake at 15 degrees C was about one third that at 35 degrees C. In conclusion, in order to maintain the aerobic condition of cytochrome aa3 in mitochondria of rat skeletal muscle, a tissue oxygen tension higher than 12 mmHg at 35 degrees C, and higher than 3 mmHg at 15 degrees C is required.