Effect of epinephrine on muscle glycogenolysis during exercise in trained men

Febbraio, M. A., D. L. Lambert, R. L. Starkie, J. Proietto,and M. Hargreaves. Effect of epinephrine on muscle glycogenolysis during exercise in trained men. J. Appl.Physiol. 84(2): 465-470, 1998.To test thehypothesis that an elevation in circulating epinephrine increasesintramuscular glycogen utilization, six endurance-trained men performedtwo 40-min cycling trials at 71 ± 2% of peak oxygen uptake in20-22°C conditions. On the first occasion, subjects wereinfused with saline throughout exercise (Con). One week later, afterdetermination of plasma epinephrine levels in Con, subjects performedthe second trial (Epi) with an epinephrine infusion, which resulted ina twofold higher (P < 0.01) plasmaepinephrine concentration in Epi compared with Con. Although oxygenuptake was not different when the two trials were compared, respiratoryexchange ratio was higher throughout exercise in Epi compared with Con(0.93 ± 0.01 vs. 0.89 ± 0.01; P < 0.05). Muscle glycogenconcentration was not different when the trials were comparedpreexercise, but the postexercise value was lower(P < 0.01) in Epi compared with Con.Thus net muscle glycogen utilization was greater during exercise withepinephrine infusion (224 ± 37 vs. 303 ± 30 mmol/kg for Con andEpi, respectively; P < 0.01). Inaddition, both muscle and plasma lactate and plasma glucoseconcentrations were higher (P < 0.05) in Epi compared with Con. These data indicate that intramuscularglycogen utilization, glycolysis, and carbohydrate oxidation areaugmented by elevated epinephrine during submaximal exercise in trainedmen.