Influence of DCA on pulmonary VO2 kinetics during moderate-intensity cycle exercise

Purpose: To test the hypothesis that pharmacological activation of the pyruvate dehydrogenase enzyme complex (PDC) with dichloroacetate (DCA) would speed phase 11 pulmonary oxygen uptake (VO2) kinetics after the onset of subsequent moderate-intensity (40-45% VO2 peak) cycle exercise. Methods: Seven healthy males (mean +/- SD age 25 +/- 4 yr, body mass 75.3 +/- 9.4 kg) performed four square-wave transitions from unloaded cycling to a work rate requiring 90% of the predetermined gas exchange threshold either with or without prior infusion of DCA (50 mg(.)kg(-1) body mass in 50 mL saline). Pulmonary VO2 was measured breath-by-breath in all tests and VO2 kinetics were determined from the averaged individual response to each condition using nonlinear regression techniques. Results: The blood [lactate] measured immediately before the onset of exercise was significantly reduced in the DCA condition (C: 1. 1 +/- 0.3 vs DCA: 0.6 +/- 0.3 mM; P +/- 0.01) consistent with successful activation of the PDC. However, DCA had no discernible effect on the rate at which VO2 increased toward the steady state after the onset of exercise as reflected in the phase 11 time constant (C: 28.5 +/- 11.8 vs DCA: 29.4 +/- 14.9 s). Conclusions: The results suggest that PDC activation does not represent a principal intramuscular limitation to VO2 kinetics after the onset of moderate-intensity exercise.