Activity of certain enzymes in the mitochondrial and cytoplasmic fractions of liver cells, myocardium and skeletal muscle of the rat during short-lasting hypothermia.

During short-lasting hypothermia in rats the activity of isocitrate dehydrogenase (E.C.1.1.1.42) and malic dehydrogenase (E.C.1.1.1.37) was determined in the mitochondrial fraction of liver cells, myocardial cells and skeletal muscle fibres of the femoral muscle and no statistically significant differences were found between the obtained values and those in a control group. On the other hand, the activity of glucose-6-phosphate dehydrogenase (E.C.1.1.1.49) in the cytoplasmic fraction of these tissues was decreased in the hypothermic rats by 46% in the liver, by 50% in the myocardium and by 59% in the skeletal muscle of the thigh. A possible cause of this reduced activity of this enzyme in hypothermia could be changes in the structure of the enzymatic protein, deficiency of the hormone activating the enzyme, that is insulin, and/or inhibition of the pentose-phosphate cycle by fatty acids released in excess.