Submitted on February 13, 2007
Accepted on July 2, 2007
Substantial working muscle glycerol turnover during two-legged cycle ergometry
Gareth A. Wallis1, Anne L. Friedlander2, Kevin A Jacobs3, Michael A. Horning4, Jill A. Fattor5, Eugene E. Wolfel6, Gary D Lopaschuk7, and George A. Brooks5*
1 Integrative Biology, UC, Berkeley, Berkeley, California, United States
2 Clinical Studies Unit, VA Palo Alto Health Care System, Palo Alto, California, United States
3 Exercise and Sports Science, University of Miami, Miami, Florida, United States
4 Integrative Biology, UC, BERKELEY, United States
5 Integrative Biology, University of California, Berkeley, California, United States
6 Division of Cardiology, University of Colorado Health Science Center, Denver, Colorado, United States
7 Pediatrics and Pharmacology, University of Alberta, Edmonton, Canada
* To whom correspondence should be addressed. E-mail: gbrooks{at}berkeley.edu.
We combined tracer and arterial-venous (a-v) balance techniques to evaluate the effects of exercise and endurance training on leg triacylglyceride turnover as assessed by glycerol exchange. Measurements on an exercising leg were taken to be a surrogate for working skeletal muscle. Eight men completed nine weeks of endurance training (5 d/week, 1 h/day, 75% VO2peak), with leg glycerol turnover determined during two pre-training trials (45% and 65% VO2peak [45% Pre, 65% Pre]) and two post-training trials (65% of pre-training VO2peak [ABT], and 65% of post-training VO2peak [RLT]) using 2H5-glycerol infusion, femoral a-v sampling and measurement of leg blood flow. Endurance training increased VO2peak by 15% (45.2±1.2 to 52.0±1.8 ml/kg/min, P<0.05). At rest, there was tracer-measured leg glycerol uptake (41±8 and 52±15 µmol/min for Pre- and Post-training respectively) even in the presence of small, but significant net leg glycerol release (-68±19 and -50±13 µmol/min respectively, P<0.05 vs. zero). Furthermore, while there was no significant net leg glycerol exchange during any of the exercise bouts, there was substantial tracer-measured leg glycerol turnover during exercise (i.e., simultaneous leg muscle uptake and leg release) (uptake, release: 45% Pre, 194±41, 214±33; 65% Pre, 217±79, 201±84; ABT, 275±76, 312±87; RLT, 282±83, 424±75 µmol/min, all P<0.05 vs. corresponding rest). Leg glycerol turnover was unaffected by exercise intensity or endurance training. In summary, simultaneous leg glycerol uptake and release (indicative of leg triacylglyceride turnover) occurs despite small or negligible net leg glycerol exchange, and further, leg glycerol turnover can be substantially augmented during exercise.
