EFFECTS OF INFUSED EPINEPHRINE ON SLOW PHASE OF O-2 UPTAKE KINETICS DURING HEAVY EXERCISE IN HUMANS

We tested the hypothesis that infused epinephrine (Epi) would augment the slow phase of oxygen uptake (VO2) during heavy exercise. Six norma l healthy males initially performed a ramp test on a cycle ergometer t o estimate the lactate threshold (LT) and determine peak VO2. Each sub ject then performed two 20-min con stant-load tests at a power output calculated to elicit a VO2 equal to estimated LT + 0.2(peak VO2 - esti mated LT) under control conditions throughout and with an intravenous infusion of Epi from minutes 10 to 20 at a rate of 100 ng.kg(-1).min(- 1). Pulmonary gas exchange variables were determined breath by breath. Arterialized venous blood was repeatedly sampled from the dorsum of t he heated hand. Epi infusion elevated (P < 0.05) plasma Epi concentrat ion (i.e., from 420 +/- 130 pg/ml at minute 10 to 2,190 +/- 410 pg/ml at minute 20) but had no effect on plasma norepinephrine or K+ concent rations. Concentrations of blood lactate and pyruvate were increased, pH was decreased, and base excess became more negative by infusion of Epi (P < 0.05). Epi infusion increased (P < 0.05) CO2 production and t he respiratory exchange ratio but had no effect on ventilation or VO2. VO2 increased (P < 0.05) to the same extent in both control (3.14 +/- 0.12 l/min at minute 10, 3.28 +/- 0.12 l/min at minute 20) and Epi in fusion (3.10 +/- 0.11 l/min at minute 10, 3.25 +/- 0.11 l/min at minut e 20) trials. We therefore conclude that neither Epi nor its associate d humoral consequences contribute significantly to the slow phase of V O2 kinetics during heavy exercise.