Liver Glycogen in Man. Effect of Different Diets and Muscular Exercise

Abstract

It is known that during heavy exercise the glucose production from the liver is increased (3, 4, 8, 9). The glucose production appears to increase successively during continued exercise, which also means that the glucose production from the liver increases concomitantly with decreasing glycogen stores in working skeletal muscle. Glucose production can increase from rest values of 100–150 mg/mm to 900–1,100 mg/mm at the end of heavy exercise (4) (Fig. 1). This increased output can be due to glycogenolysis of the glycogen store in liver or to an increased rate of gluconeogenesis. Gluconeogenic substrates are increased during exercise, both lactate and glycerol levels in blood being elevated. On the other hand, the splanchnic uptake of lactate is not increasing during the exercise period (4, 8). It was also shown many years ago that no increase in urea production occurred during exercise (6, 10). These facts are not consistent with a pronounced increase in gluconeogenesis during the exercise period.