Study on the effect of oral administration of carbocysteine on ventilatory parameters in the SO2 inhalation model of bronchitis in the rat.

In order to study the physiological correlates of the beneficial action of carbocisteine (S-carboxy-methyl-cysteine), we have measured the changes occurring in ventilatory parameters in rats made bronchitic by prolonged exposure (2 weeks) to air containing sulfur dioxide (SO2). In animals treated with distilled water (1 ml/100 g/day), statistically significant (P < 0.05) changes in respiratory frequency (-20%) and tidal volume (+31%) were found. As a result of these opposing changes, the ventilation/min was stable. Moreover, the compliance was decreased (33%, P < 0.05) and the resistance was greatly enhanced (+ 99%, P < 0.05). The concomitant administration of carbocisteine (500 mg/kg po/day) with SO2 inhalation significantly (P < 0.05) prevented the development of resistance without effecting significant changes in the other parameters except for a slight improvement in ventilation/min. In conclusion, this improved respiratory resistance in the bronchitic carbocisteine-treated animals tallies with a decrease in mucus retention associated with the return to normal of rheological characteristics of the secreted mucus.