EXERCISE-INDUCED INCREASE OF PLASMA LACTATE IS ABOLISHED BY A PREEXERCISE 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 horm onal adjustments during a subsequent exercise. Four groups of 10 rats were studied : two control groups, one at rest and one after an exerci se 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 t ype, of exercise. Epinephrine-infused rats (EI) received an infusion o f epinephrine (5 nM.kg.min-1, IV) for 20 minutes, and were rested 20 m inutes before the start pf the exercise or rest period. In the soleus muscle, epinephrine content was shown to be multiplied by 15 and 8 tim es the control values, respectively following 20 and 60 min after the end of the infusion. Control rats received a corresponding volume of s terile saline with the same schedule. The exercise lasted 49 +/- 14 vs 54 +/- 6 minutes respectively for EI and control rats (not significan t). At rest, plasma concentrations of epinephrine, norepinephrine, pla sma free fatty acids, glycerol, glucose and lactate as well as the gly cogen content of the liver, the soleus, gastrocnemius lateralis and su perficial vastus lateralis muscles were not different between saline a nd epinephrine-infused rats. Immediately after exercise, plasma lactat e 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 spl anchnic or the skeletal muscle vascular beds and thus favors lactate c learance during exercise.