Effect of exposure duration on selected enzyme indexes of cold acclimatization

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

Relative liver mass and liver activities of glucokinase, glucose-6-phosphatase, malic dehydrogenase and rate of pyruvate formation from 3-phosphoglycerate were measured in rats exposed to cold (4° ± 1°C) for periods of 2 days, 4 weeks and 5 months. The resultant data indicated the metabolic, cold-acclimatization process, insofar as the liver was concerned, consisting of three consecutive, but overlapping, stages. The first (as indicated by glucose-6-phosphatase activity) was an increased capacity to form blood sugar. This was evident after 2 days in the cold and persisted throughout all exposures. The second stage was an elevated heat-producing capacity per unit of liver weight. This was reflected in 4-week cold-exposed animals by an increased glucokinase, malic dehydrogenase and pyruvate formation rate. The third stage appeared between 1 and 5 months after entrance into the cold. It consisted of a regression of certain of the elevated activities per unit weight of liver and their replacement, insofar as the animal as a whole was concerned, by an increase in relative liver mass.