EFFECT OF CHRONIC ACETAZOLAMIDE ADMINISTRATION ON GAS-EXCHANGE AND ACID-BASE CONTROL AFTER MAXIMAL EXERCISE

Effect of chronic acetazolamide administration on gas exchange and aci d-base control after maximal exercise. J. Appl. Physiol. 76(3): 1211-1 219, 1994.-The interaction between systems regulating acid-base balanc e (i.e., CO2, strong ions, weak acids) was studied in six subjects for 10 min after 30 s of maximal isokinetic cycling during control condit ions (CON) and after 3 days of chronic acetazolamide (ChACZ) administr ation (500 mg/8 h po) to inhibit carbonic anhydrase (CA). Gas exchange was measured; arterial and venous forearm blood was sampled for acid- base variables. Muscle power output was similar in ChACZ and CON, but peak O-2, intake was lower in ChACZ; peak CO2 output was also lower in ChACZ (2,207 +/- 220 ml/min) than in CON (3,238 +/- 87 ml/min). Arter ial Pco(2), was lower at rest, and its fall after exercise was delayed in ChACZ. In ChACZ there was a higher arterial [Na+] and lower arteri al [lactate(-)] ([La-]) accompanied by lower arterial [K+] and higher arterial [Cl-] during the first part of recovery, resulting in a highe r arterial plasma strong ion difference (Sigma[cations] - Sigma[anions ]). Venoarterial (v-a) differences across the forearm showed a similar uptake of Na+, K+, Cl-, and La- in ChACZ and CON. Arterial [H+] was h igher and [HCO3-] was lower in ChACZ. Compared with CON, v-a [H+] was similar and v-a [HCO3-] was lower in ChACZ. Chronic CA inhibition impa ired the efflux of CO2 from inactive muscle and its excretion by the l ungs and also influenced the equilibration of strong ions. In contrast to our earlier study of acute CA inhibition (Kowalchuk et al. J. Appl . Physiol. 72: 278-287, 1992), the lower plasma arterial [La-] in ChAC Z was accompanied by a similar La- uptake to CON related, in part, to the greater plasma acidosis that accompanied the longer duration of CA inhibition.