Effect of prolonged cold exposure on components of the electron transport system

¹ Physiology Department, Arctic Aeromedical Laboratory, APO 731, Seattle, Washington

The effect of 3–4 weeks exposure to 5° ± 1°C on the activity of enzymes associated with the electron transport system of rat liver and gastrocnemius muscle was investigated. The enzymes included lactic, succinic and malic dehydrogenase, DPNH-cytochrome c reductase and cytochrome oxidase. Cold exposure led to increased activities on the part of succinic and malic dehydrogenase and cytochrome oxidase. Muscle tissue exhibited a greater response in these components than liver tissue. Lactic dehydrogenase and DPNH-cytochrome c reductase activities were unaffected by cold exposure in either liver or muscle. Thyroxine, 2,4-dinitrophenol, phosphate and hexokinase-glucose stimulated the activity of succinic dehydrogenase activities of liver tissue, with hexokinase-glucose producing the greatest effect. The degree of stimulation by these agents was the same, however, for tissue from cold exposed animals as it was for controls. It was concluded that the increased tissue oxygen consumption in the cold-acclimatized rat was attributable to at least three mechanisms: a) an increased enzyme concentrations; b) a stimulation of latent enzyme activity; and c) an uncoupling of oxidative phosphorylation.