EFFECT OF GRADED EPINEPHRINE INFUSION ON BLOOD LACTATE RESPONSE TO EXERCISE

In an attempt to determine whether the lactate threshold (LT) is the r esult of a sudden increase in plasma epinephrine (Epi), eight healthy college-aged males (22.4 +/- 0.4 yr) were recruited to perform three c ycle ergometer exercise tests. Each subject performed a graded exercis e test (GXT) to determine LT, Epi threshold, and norepinephrine thresh old (64.6 +/- 2.4, 62.5 +/- 2.4, and 60.8 +/- 4.3% peak oxygen uptake, respectively). Each subject also completed, in random order, two 30-m in submaximal (20% peak oxygen uptake below LT) exercise tests. During one test, graded Epi infusions were carried out at rates of 0.02-0.12 mu g . kg(-1). min(-1); the other served as a control test. Infusion resulted in plasma Epi concentrations similar to those observed during GXT. The increase in blood lactate with Epi infusion was significantl y greater than that during the control test (3.0 +/- 0.3 vs. 1.4 +/- 0 .1 mmol/l at minute 30) but did not approach levels exhibited during G XT. We suggest an interaction of the increasing plasma Epi with other factors may be responsible for the sudden increase in blood lactate du ring graded exercise.