N-Acetylcysteine protects the rat diaphragm from the decreased contractility associated with controlled mechanical ventilation.

OBJECTIVE

Controlled mechanical ventilation results in diaphragmatic dysfunction, and oxidative stress has been shown to be an important contributor to ventilator-induced diaphragm dysfunction. We hypothesized that the administration of an antioxidant, N-acetylcysteine, would restore the redox balance in the diaphragm and prevent against the deleterious effects of controlled mechanical ventilation.

DESIGN

Randomized, controlled experiment.

SETTINGS

Basic science animal laboratory.

SUBJECTS

Male Wistar rats, 14 wks old.

INTERVENTIONS

Anesthetized rats were submitted for 24 hrs to either spontaneous breathing receiving 150 mg/kg N-acetylcysteine (SBNAC) or saline (SBSAL) or to controlled mechanical ventilation receiving 150 mg/kg N-acetylcysteine (MVNAC) or saline (MVSAL).

MEASUREMENTS AND MAIN RESULTS

After 24 hrs of controlled mechanical ventilation, diaphragmatic force production was significantly lower in MVSAL compared with all groups. Importantly, administration of N-acetylcysteine completely abolished this controlled mechanical ventilation-induced diaphragmatic contractile dysfunction. Diaphragmatic protein oxidation was significantly increased after 24 hrs of controlled mechanical ventilation (+53%, p < .01) in MVSAL animals, whereas administration of N-acetylcysteine prevented this controlled mechanical ventilation-induced oxidative stress. Diaphragmatic 20S proteasome activity was increased in MVSAL (+62%, p < .05). Further, compared with SBSAL, diaphragm caspase-3 activity was significantly increased in MVSAL (+279%, p < .001), and N-acetylcysteine treatment provided partial protection against caspase-3 activation. Diaphragmatic calpain activity was significantly increased after controlled mechanical ventilation (+137%, p < .001) in MVSAL animals, but N-acetylcysteine treatment protected against this event. Finally, significant negative correlations existed between calpain activity and diaphragm force production (r from -0.56 to -0.49, p < .05).

CONCLUSIONS

These data show that the administration of N-acetylcysteine protects the diaphragm from the deleterious effects of controlled mechanical ventilation. Specifically, N-acetylcysteine prevents against controlled mechanical ventilation-induced diaphragmatic oxidative stress and proteolysis and abolishes controlled mechanical ventilation-induced diaphragmatic contractile dysfunction.