title: Effects of infused epinephrine on slow phase of O2 uptake kinetics during heavy exercise in humans.
abstract: We tested the hypothesis that infused epinephrine (Epi) would augment the slow phase of oxygen uptake (VO2) during heavy exercise. Six normal healthy males initially performed a ramp test on a cycle ergometer to estimate the lactate threshold (LT) and determine peak VO2. Each subject then performed two 20-min constant-load tests at a power output calculated to elicit a VO2 equal to estimated LT + 0.2(peak VO2--estimated 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 the heated hand. Epi infusion elevated (P < 0.05) plasma Epi concentration (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+ concentrations. 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 the 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 infusion (3.10 +/- 0.11 l/min at minute 10, 3.25 +/- 0.11 l/min at minute 20) trials. We therefore concluded that neither Epi nor its associated humoral consequences contribute significantly to the slow phase of VO2 kinetics during heavy exercise.
authors.affiliation: Department of Physiology, University of California, Los Angeles, School of Medicine 90024.
authors.forename: G A
authors.initials: GA
authors.lastname: Gaesser
authors.forename: S A
authors.initials: SA
authors.lastname: Ward
authors.forename: V C
authors.initials: VC
authors.lastname: Baum
authors.forename: B J
authors.initials: BJ
authors.lastname: Whipp
mesh_terms: D000328:Adult; D000818:Animals; D001784:Blood Gas Analysis; D002851:Chromatography, High Pressure Liquid; D004837:Epinephrine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007262:Infusions, Intravenous; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D013058:Mass Spectrometry; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012129:Respiratory Function Tests
chemical_list: D007773:Lactates; D019344:Lactic Acid; D004837:Epinephrine