Initial stages of intermediary glucose catabolism in the hibernator and nonhibernator

Abstract

In the Arctic ground squirrel, hibernation caused a marked hypoglycemia and a twofold increase in myocardial and skeletal muscle glycogen, but had no effect on liver glycogen. When assayed at 30 C, hibernation led to a moderate increase in the glucokinase and glucose-6-phosphate dehydrogenase activity of the myocardium. Finally, it also caused a sharp reduction in the glucose-6-phosphate dehydrogenase activity and almost a complete obliteration of phosphorylase activity in the liver. Between species, the laboratory rat exhibited about 50% more myocardial glucose-6-phosphate dehydrogenase and about twice as much phosphorylase as the myocardium of the awake squirrel. The liver of the awake squirrel had about 50% more glucose-6-phosphatase, about 60% more phosphorylase, about twice as much glucokinase, and about four times as much glucose-6-phosphatase as the liver of the rat. A number of correlated enzyme activities were observed. The mechanisms underlying the hypoglycemia and net glycogen synthesis of hibernation and the species differences in carbohydrate metabolism and lipogenic capacity are discussed.