Effect of infusing epinephrine on liver and muscle glycogenolysis during exercise in rats

To determine the possibility of a threshold concentration of plasma epinephrine that stimulates liver glycogenolysis during exercise, adrenodemedullated (ADM) and sham-operated (SHAM) rats were infused with saline or epinephrine at rates that produced plasma concentrations ranging between 0.01 ng/ml (0.06 nM) and 4.3 ng/ml (23.7 nM). During the infusion rats were run on a rodent treadmill for 0, 30, or 60 min at 21 m/min up a 15% grade. Liver glycogen decreased at similar rates in all exercising rats regardless of plasma epinephrine concentration. Epinephrine infusion stimulated significant muscle glycogen depletion in the soleus and red and white vastus lateralis muscles. ADM saline-infused animals exhibited the least muscle glycogen depletion. Blood glucose and lactate in exercising ADM rats increased as the epinephrine infusion concentration increased. During exercise, there was no epinephrine concentration that stimulated liver glycogenolysis more effectively than physiological saline.