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 O2 uptake (V(O2)) 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, <VE(T)) or to a V(O2) corresponding to approximately 50% of the difference between the work rate at VE(T) and peak V(O2) (>VE(T). 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- (<VE(T)) or a three-component exponential model (>VE(T)). 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 <VE(T). At work rates >VE(T), 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 >VE(T) than for <VE(T) exercise. [La-]pl increased above 0-W cycling values during <VE(T) and >VE(T) exercise but was lower at the end of the transition during Acz (1.4 +/- 0.2 and 7.1 +/- 0.5 mmol/l for <VE(T) and >VE(T) respectively) than during Con (2.0 +/- 0.2 and 9.8 +/- 0.9 mmol/l for <VE(T) and >VE(T), respectively). CA inhibition does not affect O2 utilization at the onset of <VE(T) or >VE(T) exercise, suggesting that the contribution of oxidative phosphorylation to the energy demand is not affected by acute CA inhibition with Acz.
School of Kinesiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7.
B W
BW
Scheuermann
J M
JM
Kowalchuk
D H
DH
Paterson
D A
DA
Cunningham
D000086:Acetazolamide / Q000494:pharmacology*; D000328:Adult; D001835:Body Weight; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007700:Kinetics; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
D000086:Acetazolamide