Effect of exercise on net hepatic uptake of lactate, pyruvate, alanine, and glycerol in sheep.

Gluconeogenesis increases during exercise, which is associated with elevated concentrations of lactate and glycerol in blood. This study was undertaken to determine if the exercise-induced increase in gluconeogenesis is due to increased hepatic extraction efficiency of glucose precursors. The net hepatic uptake and extraction ratios were determined for selected glucose precursors before and during exercise. The hepatic uptake of lactate and glycerol increased during exercise in fed and fasted animals, but extraction ratios of lactate and glycerol increased only in fed animals. Thus, the exercise-induced increase in gluconeogenesis is due to increased substrate supply and to hepatic extraction efficiency under certain circumstances, which is comparable to the situation in man.