Carbonic anhydrase inhibition delays plasma lactate appearance with no effect on ventilatory threshold

The effect of carbonic anhydrase (CA) inhibition with acetazolamide (Acz, 10 mg/kg body wt iv) on exercise performance and the ventilatory (VET) 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)). V(over dot)ET [expressed as O-2 uptake (V(over dot)O-2), ml/min] was determined using the V-slope method. LaT (expressed as V(over dot)O-2, 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 Act sutdies [339 +/- 14 vs. 315 +/- 14 (SE) W]. Submaximal exercise V(over dot)O-2 was similar in Act and Con; the lower V(over dot)O-2 at exhaustion in Act than in Con (3.824 +/- 0.150 vs. 4.283 +/- 0.148 l/min) was appropriate for the lower WR. CO2 output (V(over dot)CO2) was lower in Act than in Con at exercise intensities greater than or equal to 125 W and at exhaustion (4.375 +/- 0.158 vs. 5.235 +/- 0.148 l/min), [La-](pl) was lower in Act than in Con during submaximal exercise greater than or equal to 150 W and at exhaustion (7.5 +/- 1.1 vs. 11.5 +/- 1.1 mmol/l). V(over dot)ET was similar in Act and Con (2.483 +/- 0.086 and 2.362 +/- 0.110 l/min, respectively), whereas the LaT occurred at a higher V(over dot)O-2 in Act than in Con (2.738 +/- 0.223 vs. 2.190 +/- 0.235 l/min). CA inhibition with Act is associated with impaired elimination of CO2 during the non-steady-state condition of ramp exercise. The similarity in VET in Con and Act 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 Act treatment.