Journal of Applied Physiology
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J Appl Physiol 85: 1384-1393, 1998;
8750-7587/98 $5.00
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Vol. 85, Issue 4, 1384-1393, October 1998

O2 uptake kinetics after acetazolamide administration during moderate- and heavy-intensity exercise

Barry W. Scheuermann1, John M. Kowalchuk1,2, Donald H. Paterson1, and David A. Cunningham1,2

1 School of Kinesiology and 2 Department of Physiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7

Inhibition of carbonic anhydrase (CA) is associated with a lower plasma lactate concentration ([La-]pl) during fatiguing exercise. We hypothesized that a lower [La-]pl may be associated with faster O2 uptake (VO2) kinetics during constant-load exercise. Seven men performed cycle ergometer exercise during control (Con) and acute CA inhibition with acetazolamide (Acz, 10 mg/kg body wt iv). On 6 separate days, each subject performed 6-min step transitions in work rate from 0 to 100 W (below ventilatory threshold, <VET) or to a VO2 corresponding to ~50% of the difference between the work rate at VET and peak VO2 (>VET). Gas exchange was measured breath by breath. Trials were interpolated at 1-s intervals and ensemble averaged to yield a single response. The mean response time (MRT, i.e., time to 63% of total exponential increase) for on- and off-transients was determined using a two- (<VET) or a three-component exponential model (>VET). Arterialized venous blood was sampled from a dorsal hand vein and analyzed for [La-]pl. MRT was similar during Con (31.2 ± 2.6 and 32.7 ± 1.2 s for on and off, respectively) and Acz (30.9 ± 3.0 and 31.4 ± 1.5 s for on and off, respectively) for work rates <VET. At work rates >VET, MRT was similar between Con (69.1 ± 6.1 and 50.4 ± 3.5 s for on and off, respectively) and Acz (69.7 ± 5.9 and 53.8 ± 3.8 s for on and off, respectively). On- and off-MRTs were slower for >VET than for <VET exercise. [La-]pl increased above 0-W cycling values during <VET and >VET exercise but was lower at the end of the transition during Acz (1.4 ± 0.2 and 7.1 ± 0.5 mmol/l for <VET and >VET, respectively) than during Con (2.0 ± 0.2 and 9.8 ± 0.9 mmol/l for <VET and >VET, respectively). CA inhibition does not affect O2 utilization at the onset of <VET or >VET exercise, suggesting that the contribution of oxidative phosphorylation to the energy demand is not affected by acute CA inhibition with Acz.

blood lactate; carbonic anhydrase; on- and off-transients


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