Factors of lowered respiratory CO2 sensitivity by acetazolamide in anaesthetized rabbits

• Published in: Central European journal of medicine Vol. 1; no. 4; pp. 356 - 369
• Main Authors: Kiwull-Schöne, Heidrun, Teppema, Luc, Kiwull, Peter
• Format: Journal Article
• Language: English
• Published: Berlin Versita 01.12.2006; Walter de Gruyter GmbH; De Gruyter
• Subjects: Acetazolamide; CO2 sensitivity; metabolic acidosis; rabbits; respiratory muscle fatigue
• ISSN: 2391-5463; 1895-1058; 2391-5463; 1644-3640
• DOI: 10.2478/s11536-006-0034-7

The carbonic anhydrase (CA) inhibitor acetazolamide is a classic drug to treat patients with breathing disorders. Recent studies in rabbits showed that low-dose acetazolamide (not causing appreciable inhibition of red cell CA) significantly weakened respiratory muscle performance, accompanied by diminished ventilatory CO2-sensitivity, which implies stabilizing loop-gain properties. Now is aimed to explore the interaction of these factors under conditions of complete CA-inhibition by acetazolamide in a higher dose-range. In anesthetized rabbits (N=7), acetazolamide (up to 75 mg·kg−1) distinctly lowered the base excess (to-7.6 ± 0.9mM, mean ± SEM) without respiratory compensation of arterial pH. Ventilatory CO2-sensitivity was nearly abolished to 15.1 ± 5.2% of control, but the transmission of a CO2-mediated rise in tidal phrenic activity into respiratory work was only reduced by 51.6 ± 6.4%, P < 0.001, not very much more than (~38%) already observed at low-doses. Thus, the large reduction of ventilatory CO2-sensitivity in the high-dose range cannot be ascribed to respiratory muscle weakening, but rather may relate to complete inhibition of red cell CA. Conversely, CA-inhibition may not be the only cause for the weakening effect of acetazolamide on (respiratory) muscles. Adverse effects on respiratory muscles, impaired CO2-transport and acid-base imbalance may limit to make use of stabilizing effects on breathing control functions by high-dose acetazolamide.