Effect of prolonged cold exposure on the glycolytic enzymes of liver and muscle

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

Liver and muscle tissue from male Sprague-Dawley rats, exposed to 5 ± 1°C for 3–4 weeks, were assayed for the activities of selected glycolytic enzymes. When compared to control animals maintained at 25 ± 1°C, the cold-exposed animals showed an increase in liver glucose-6-phosphatase, an increase in liver and muscle glucokinase, a decrease in glucose-6-phosphate and 6-phosphogluconic dehydrogenase in both liver and muscle, and an increase in the rate of pyruvate formation from 3-phosphoglycerate in liver tissue. Assays of liver and muscle phosphoglucomutase, total liver and muscle phosphorylase and phosphorylase a and b in muscle failed to show any cold effect. The results indicate the cold-exposed rat has the enzyme capacities for: an increased utilization of free glucose, an increased glycogenolysis either to free glucose to pyruvate and an increased gluconeogenesis. They also indicate a decreased hexose monophosphate shunt activity. Little evidence could be found to indicate an epinephrine-induced activation of phosphorylase in the cold-exposed animals.