Exercise-induced increase of plasma lactate is abolished by a pre-exercise epinephrine infusion

The purpose of this study was to determine the effect of a higher than normal epinephrine content in skeletal muscles, on metabolic and hormonal adjustments during a subsequent exercise. Four groups of 10 rats were studied: two control groups, one at rest and one after an exercise leading to exhaustion on a treadmill (28 m.min-1, 8% grade) and two epinephrine-infused groups (EI), one at rest and one after the same type of exercise. Epinephrine-infused rats (EI) received an infusion of epinephrine (5 nM.kg.min-1, i.v.) for 20 minutes, and were rested 20 minutes before the start of the exercise or rest period. In the soleus muscle, epinephrine content was shown to be multiplied by 15 and 8 times the control values, respectively following 20 and 60 min after the end of the infusion. Control rats received a corresponding volume of sterile saline with the same schedule. The exercise lasted 49 +/- 14 vs 54 +/- 6 minutes respectively for EI and control rats (not significant). At rest, plasma concentrations of epinephrine, norepinephrine, plasma free fatty acids, glycerol, glucose and lactate as well as the glycogen content of the liver, the soleus, gastrocnemius lateralis and superficial vastus lateralis muscles were not different between saline and epinephrine-infused rats. Immediately after exercise, plasma lactate concentration was not increased after exercise in EI vs (2.26 +/- 0.39 vs 4.53 +/- 0.73 mM). One possible explanation of this observation is that re-released epinephrine might induce a vasodilation in the splanchnic or the skeletal muscle vascular beds and thus favors lactate clearance during exercise.