Effect of adrenodemedullation on metabolic responses to high-intensity exercise

To determine the role of epinephrine in glycogenolysis during high-intensity exercise, rats were adrenodemedullated (ADM) or sham operated (SHAM) and run for either 30 min at 38 m/min or for 5 min at 27, 38, or 48 m/min up a 15% grade. At the end of exercise the rats were anesthetized by intravenous injection of pentobarbital sodium. Liver, blood, and muscle samples were obtained. Plasma epinephrine values were 5.9 and 0.3 nM for SHAM and ADM animals, respectively, after 30 min of exercise. Liver glycogen decreased by 16 and 21 mg/g in the SHAM and ADM groups, respectively, and liver cAMP increased significantly in both groups. Glycogen in the soleus muscle decreased 80% in the SHAM but only 43% in the ADM animals after 30 min of exercise. The exercise-induced hyperglycemia observed in the SHAM animals was not present in the ADM animals. The responses of cyclic AMP, soleus glycogen, and blood glucose were similar in both the 5- and 30-min exercise groups. During intense exercise, epinephrine is unessential for stimulating liver glycogenolysis but does play an important role in stimulating glycogenolysis in the soleus muscle and in establishing exercise-induced hyperglycemia.