Ga. Gaesser et al., EFFECTS OF INFUSED EPINEPHRINE ON SLOW PHASE OF O-2 UPTAKE KINETICS DURING HEAVY EXERCISE IN HUMANS, Journal of applied physiology, 77(5), 1994, pp. 2413-2419
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.