| This project was designed to study the role of epinephrine in control of liver and muscle glycogenolysis. Fasted or fed sham-operated (SO) and adrenodemedullated (ADM) rats were run at 21 meters/min up a 10-15% grade on treadmill for 30 min, 80 min or to exhaustion. Saline, epinephrine, glucose, lactate or epinephrine + insulin were infused into the rats. ADM rats exhibited impaired muscle glycogenolysis, reduced endurance, hypoglycemia, low blood lactate and elevated plasma insulin compared to SO rats. Liver glycogen declined to the same extent in ADM and SO exercising rats. Epinephrine and glucose infusion restored endurance. Elevated plasma insulin did not impair epinephrine-stimulated muscle glycogenolysis. These data show that circulating epinephrine is unessential for stimulating liver glycogenolysis. After liver glycogen is depleted, epinephrine is essential for preventing hypoglycemia and allowing continuation of exercise. |
