Epinephrine Infusion Does Not Enhance Net Muscle Glycogenolysis During Prolonged Aerobic Exercise

Abstract

The role of physiological elevations of plasma epinephrine concentration on muscle glycogenolysis during prolonged exercise was investigated. Eight healthy volunteers cycled for 90 min at 65% VO2max on two occasions; once with an infusion of epinephrine (EPI) and once without (control). Biopsy samples were taken from the vastus lateralis muscle both prior to and following exercise for the analysis of muscle glycogen. EPI infusion significantly elevated venous plasma EPI ~2.5-fold over control values throughout exercise (90 min: 5.78 ± 0.95 vs. 2.35 ± 0.49 nM). EPI infusion did not significantly alter net glycogenolysis as compared to control (310.0 ± 30.8 vs. 299.5 ± 41.1 mmol glucosyl units/kg dry mass). Venous concentrations of plasma FFA and whole blood glycerol were unaffected by EPI infusion. Whole blood glucose was significantly elevated during EPI infusion at 10, 30, 60 and 90 min of exercise compared to control values. Whole blood lactate was elevated to a greater extent during EPI infusion as compared to control at 10, 30, and 60 min of exercise. In conclusion, EPI infusion had no effect on muscle glycogenolysis and appeared to have little effect on adipose tissue lipolysis. The explanation for the elevation of blood lactate is unknown while the elevation in blood glucose suggests that EPI infusion potentiated liver glycogenolysis. Key words: muscle metabolism, plasma catecholamines, blood lactate, lipolysis, blood glucose