Effects of acetazolamide on medullary extracellular pH and $${\text{P}}_{{\text{CO}}_{\text{2}} } $$ and on ventilation in peripherally chemodenervated catsand on ventilation in peripherally chemodenervated cats

The responses of ventilation and of medullary extracellular fluid (ECF) pH and \({\text{P}}_{{\text{CO}}_{\text{2}} } \) , to an intravenous (i. v.) infusion of 50 mg/kg acetazolamide (an inhibitor of carbonic anhydrase), were measured in cats anaesthetized with chloralose and urethane, in which both bilateral vagotomy and carotid nerve section had been performed. After 2 h, it was observed that: acetazolamide caused an acidosis in medullary ECF which was still developing after 2 h, reflected by a progressive fall in pH (mean = 0.215 pH units in 2 h), while ECF \({\text{P}}_{{\text{CO}}_{\text{2}} } \) showed an insignificant rise of about 1 kPa; acetazolamide caused a considerable rise in ventilation, which largely developed in the first 15 min after drug infusion; the direction of the ECF acid-base responses in the first 15 min varied, whereas that of the ventilatory response did not. Further-more, the time course of the former developed quite differently from the latter. It was therefore concluded that the observed changes in medullary ECF pH and \({\text{P}}_{{\text{CO}}_{\text{2}} } \) can not explain the large and fast ventilatory response of acetazolamide.