Substrate Turnover and Oxidation During Moderate-Intensity Exercise Following Acute Plasma Volume Expansion

B. D. Roy; H. J. Green; S. M. Grant; M. A. Tarnopolsky

doi:10.1055/s-2002-20522

Hormone and Metabolic Research, Table of Contents

Horm Metab Res 2002; 34(2): 93-101
DOI: 10.1055/s-2002-20522

Original Clinical

Substrate Turnover and Oxidation During Moderate-Intensity Exercise Following Acute Plasma Volume Expansion

B. D. Roy ¹ , H. J. Green ¹ , S. M. Grant ¹ , M. A. Tarnopolsky ²

¹ Department of Kinesiology, University of Waterloo, Waterloo, Canada
² Department of Medicine/Kinesiology, McMaster University, Hamilton, Canada

Abstract

In previous work using prolonged, light cycle exercise, we were unable to demonstrate an effect of acute plasma volume (PV) expansion on glucose kinetics or substrate oxidation, despite a decline in whole-body lipolysis (Phillips et al., 1997). However, PV is known to decrease arterial O₂ content. The purpose of this study was to examine whether substrate turnover and oxidation would be altered with heavier exercise where the challenge to O₂ delivery is increased. Eight untrained males (VO_2max = 3.52 ± 0.12 l/min) twice performed 90 min of cycle ergometry at 62 % VO_2peak, both prior to (CON) and following induced plasma volume expansion (Dextran [6 %] or Pentaspan [10 %]) (6.7 ml/kg) (PVX). Glucose and glycerol kinetics were determined with primed constant infusions of [6.6-²H₂] glucose and [²H₅] glycerol, respectively. PVX resulted in a 15.8 ± 2.2 % increase (p < 0.05) in PV. Glucose and glycerol appearance (R_a) and utilization (R_d), although increasing progressively (p < 0.05) with exercise, were not different between conditions. Similarly, no differences in substrate oxidation, either fat or carbohydrate, were observed between the two conditions. Prolonged exercise resulted in an increase (p < 0.05) in plasma glucagon and a decrease (p < 0.05) in plasma insulin during both conditions. With PVX, the exercise-induced increase in glucagon was diminished (p < 0.05). We conclude that impairment in O₂ content mediated by an elevated PV does not alter glucose, and glycerol kinetics or substrate oxidation even at moderate exercise intensity.

Key words

Glucose Turnover - Glycerol Turnover - Lipolysis - Stable Isotopes - Exercise - Hypervolemia

Full Text

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Dr. H. J. Green

Department of Kinesiology · University of Waterloo

Waterloo, ON, N2L3G1 · Canada

Phone: + 1 (519) 888-4567, x3454

Fax: + 1 (519) 885-0470

Email: green@healthy.uwaterloo.ca