Effect of epinephrine on slow component of oxygen consumption during heavy exercise

Abstract

Prior heavy exercise bout on cycle ergometer changes the V O2 kinetics of a subsequent heavy exercise bout. These changes are an increase in V O2 fundamental component (Ap) and a reduction in V O2 slow component (V O2sc) without changing primary component time constant. Infusion of epinephrine has shown to increase resting V O2 levels in humans at rest and during exercise. To test the effect of epinephrine on V O2 kinetics, epinephrine was injected at the beginning of exercise and the kinetics of oxygen consumption was compared with the oxygen kinetics of a prior and second exercise bouts. Seven healthy physically active male participants volunteered for the study. Participants performed 8 min bout of heavy exercise on an electrically braked cycle ergometer preceded by 1) 8 min heavy exercise bout with a 6 min rest period in between and 2) 0.10 mg epinephrine intra muscular injection on deltoid immediately followed by 5 minutes rest to reach it’s onset of action. Same protocol was performed in two different days. Bloods samples to measure plasma [Epi] and [NE] were taken ten times in total during each testing day. Fundamental amplitude (Ap) of epinephrine bout was significantly higher than the prior cycling bout (p < 0.05). Slow component of oxygen uptake (As’) was significantly lower in the second cycling bout (222 + 77.4 mlO2*min-1) compared to the prior cycling bout (369.4 + 135.4 mlO2*min-1;p < 0.05) and to epinephrine cycling bout (357.1 + 178.6 mlO2*min-1; p = 0.05). [Epi] at end of epinephrine bout was significantly higher when compared to blood samples taken, pre-prior, 2-min into prior, pre-second, 2-min into second and pre-Epi injection (p < 0.05). The results of the study demonstrate that epinephrine injection increased magnitude of Ap and V O2end compared to prior heavy bout. However, it had no effect on V O2 baseline, effective time constant, or V O2sc compared to prior heavy bout. No significance differences were found in V O2 kinetics when comparing second heavy bout and epinephrine injection heavy bout. Results show that the increase in [Epi] may be responsible in part for the changes seen in V O2 kinetics of second heavy exercise bout.