EFFECT OF EPINEPHRINE ON MUSCLE GLYCOGENOLYSIS DURING EXERCISE IN TRAINED MEN

To test the hypothesis that an elevation in circulating epinephrine in creases intramuscular glycogen utilization, six endurance-trained men performed two 40-min cycling trials at 71 +/- 2% of peak oxygen uptake in 20-22 degrees C conditions. On the first occasion, subjects were i nfused with saline throughout exercise (Con). One week later, after de termination of plasma epinephrine levels in Con, subjects performed th e second trial (Epi) with an epinephrine infusion, which resulted in a twofold higher (P < 0.01) plasma epinephrine concentration in Epi com pared with Con. Although oxygen uptake was not different when the two trials were compared, respiratory exchange ratio was higher throughout exercise in Epi compared with Con(0.93 +/- 0.01 vs. 0.89 +/- 0.01; P < 0.05). Muscle glycogen concentration was not different when the tria ls were compared preexercise, but the postexercise value was lower (P < 0.01) in Epi compared with Con. Thus net muscle glycogen utilization was greater during exercise with epinephrine infusion (224 +/- 37 vs. 303 +/- 30 mmol/kg for Con and Epi, respectively; P < 0.01). In addit ion, both muscle and plasma lactate and plasma glucose concentrations were higher (P < 0.05) in Epi compared with Con. These data indicate t hat intramuscular glycogen utilization, glycolysis, and carbohydrate o xidation are augmented by elevated epinephrine during submaximal exerc ise in trained men.