Effect of hypothermia on skeletal muscle metabolism in perfused rat hindlimb.

Temperature-induced metabolic change was studied with isolated rat hindlimb muscle to elucidate how tissue viability is maintained under hypothermia. The hindlimb was perfused with Krebs-bicarbonate buffer containing 4% (w/v) polyvinylpyrrolidone (PVP-40T) in a flowthrough mode at 35-8 degrees C. When the temperature was lowered, the following results were observed: (i) Vascular resistance (defined as perfusion pressure divided by flow rate) increased proportionally with elevation of the viscosity of the perfused medium, suggesting that the capillary bed in the perfused muscle is maintained under a similar condition under these temperatures; (ii) the Arrhenius plot of the O2 uptake rate showed a break at ca. 20 degrees C; (iii) the rates of O2 uptake and lactate release decreased, but the lactate/pyruvate ratio increased even under aerobic conditions; (iv) oxygenation of myoglobin and oxidation of cytochromes increased, suggesting a reduced electron-transfer rate in spite of improved or sufficient oxygenation of the tissue. Based on these results, we concluded that oxidative phosphorylation is more affected by temperature than glycolysis, and thus under hypothermia, the role of glycolysis in energy production increases in rat skeletal muscle, especially below 20 degrees C.