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

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 O-2 uptake ((V)over dot O-2) 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 B-min step transitions in work rate from 0 to 100 W (below ventilatory threshold, <(V)over dot ET) or to a (V)over dot O-2, corresponding to similar to 50% of the difference between the work rate at (V)over dot ET and peak (V)over dot O-2 (>(V)over dot ET). 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- (<(V)over dot ET) or a three-component exponential model (>(V)over dot ET). 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 <(V)over dot ET. At work rates >(V)over dot ET, 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 >(V)over dot ET than for <(V)over dot ET exercise. [La-](pl) increased above 0-W cycling values during <(V)over ET and >(V)over dot ET exercise but was lower at the end of the transition during Acz (1.4 +/- 0.2 and 7.1 +/- 0.5 mmol/l for <(V)over dot ET and >(V)over dot ET, respectively) than during Con (2.0 +/- 0.2 and 9.8 +/- 0.9 mmol/l for <(V)over dot ET and (V)over dot ET respectively). CA inhibition does not affect O-2 utilization at the onset of <(V)over dot ET or >(V)over dot ET exercise, suggesting that the contribution of oxidative phosphorylation to the energy demand is not affected by acute CA inhibition with Acz.