Role of cyclic AMP in regulation of hepatic glucose production during exercise

Cyclic AMP increases in liver during exercise, the magnitude of the increase being dependent on duration and intensity of the exercise. Within limits, the increase in cAMP is closely correlated with the rate of glycogenolysis and with the exercise intensity. It is unlikely that epinephrine is involved in determining cAMP concentration in liver during exercise. Adrenodemedullated rats show no impairment in exercise-induced liver glycogenolysis or in the increase in cAMP. When epinephrine is infused at different rates into exercising rats, liver cAMP appears to be unrelated to plasma epinephrine. The rise in plasma glucagon is likely responsible for the increase in hepatic cAMP during exercise. The increase in cAMP is apparently necessary for maintaining low levels of fructose-2,6-bisphosphate (the activator of PFK-1 and inhibitor of fructose-1,6-bisphosphate) in liver. The low fructose-2,6-bisphosphate concentration would be expected to result in an increase rate of gluconeogenesis during exercise.