Inhaled carbon dioxide inhibits lower airway nitric oxide formation in the guinea pig.

The present study addressed the effect of inhaled carbon dioxide on lower airway nitric oxide formation in normoxic anaesthetized guinea pigs. Ventilation with carbon dioxide (1.5, 3, 6, 9 and 12%) induced a concentration-dependent decrease in the basal concentration of nitric oxide in exhaled tracheal air. A maximal reduction in exhaled nitric oxide of approximately 25% was induced by 12% carbon dioxide in inhaled air. Ventilation with positive end-expiratory pressure (7 cmH2O) increased the concentration of exhaled nitric oxide. Inhalation of carbon dioxide had a larger, concentration-dependent, inhibitory effect (maximally 60%) on the lower airway nitric oxide formation induced by ventilation with positive end-expiratory pressure, as compared with the effect on the basal concentration of nitric oxide. The results show that inhaled carbon dioxide suppresses lower airway nitric oxide excretion in the guinea pig. Endogenous carbon dioxide might exert effects through regulation of endogenous nitric oxide formation, for example in the regulation of airway tone or in ventilation-perfusion matching.