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1 Centre for Activity and Ageing, School of Kinesiology, and 2 Department of Physiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7
The effect of carbonic anhydrase (CA) inhibition with
acetazolamide (Acz, 10 mg/kg body wt iv) on exercise performance and the ventilatory
(
ET) and
lactate (LaT) thresholds was studied in seven men during ramp exercise
(25 W/min) to exhaustion. Breath-by-breath measurements of gas exchange
were obtained. Arterialized venous blood was sampled from a dorsal hand
vein and analyzed for plasma pH,
PCO2, and lactate concentration
([La
]pl).
ET
[expressed as O2 uptake
(
O2), ml/min] was
determined using the V-slope method. LaT (expressed as
O2, ml/min) was determined
from the work rate (WR) at which
[La
]pl
increased 1.0 mM above rest levels. Peak WR was higher in control (Con)
than in Acz sutdies [339 ± 14 vs. 315 ± 14 (SE) W].
Submaximal exercise
O2 was
similar in Acz and Con; the lower
O2 at exhaustion in Acz
than in Con (3.824 ± 0.150 vs. 4.283 ± 0.148 l/min) was
appropriate for the lower WR. CO2
output (
CO2) was lower in
Acz than in Con at exercise intensities
125 W and at exhaustion
(4.375 ± 0.158 vs. 5.235 ± 0.148 l/min).
[La
]pl
was lower in Acz than in Con during submaximal exercise
150 W and at
exhaustion (7.5 ± 1.1 vs. 11.5 ± 1.1 mmol/l).
ET was similar in Acz and Con (2.483 ± 0.086 and 2.362 ± 0.110 l/min, respectively), whereas the LaT occurred at a higher
O2 in Acz than in Con
(2.738 ± 0.223 vs. 2.190 ± 0.235 l/min). CA inhibition with Acz
is associated with impaired elimination of
CO2 during the non-steady-state
condition of ramp exercise. The similarity in
ET in Con
and Acz suggests that La
production is similar between conditions but
La
appearance in plasma is
reduced and/or La
uptake by
other tissues is enhanced after the Acz treatment.
ramp exercise; acetazolamide; exercise performance; acid-base status
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