Interrelationships of diet and cold exposure on selected liver glycolytic enzymes

¹ Department of Biochemistry, Arctic Aeromedical Laboratory, APO 731, Seattle, Washington

The effect of a 28-day cold exposure (4 ± 1 C) on selected glycolytic enzymes of the liver was studied in rats subsisting on carbohydrate free diets high in fat or protein and on a 65% glucose diet. Cold exposure increased glucose-6-phosphatase activity on all diets, but had an appreciable effect on glucokinase activity only in the rats fed high carbohydrate diets. The activity of phosphorylase was not affected by cold. "Pyruvate formation," like glucose-6-phosphatase activity, was increased significantly in all dietary groups by cold exposure. The extremely low activity of glucose-6-phosphate dehydrogenase in the rats fed high fat diets was unaffected by cold exposure. These results are interpreted to mean that, on a carbohydrate free diet, imposition of cold leads to increased reversal of pyruvate formation which is reflected in increased production of free glucose, whereas hexose monophosphate shunt activity and glycogenesis remain unaffected. Even on a high carbohydrate diet, the capacity for hepatic glucose production appears to be increased, possibly as a result of increased periodic demands on the part of extrahepatic tissues.