Naloxone administration and ventilation in awake cats

Naloxone, an opiate antagonist, was administered to unrestrained awake cats to determine whether endogenous opioids tonically inhibit breathing. Whole body plethysmography was used to assess ventilation. Minute ventilation, tidal volume and breathing frequency were determined in each of 4 cats before and after 0.4 and 4.0 mg/kg naloxone. Analysis of variance did not show a significant difference between ventilatory values obtained before and after naloxone administration. Similarly, end-tidal pCO2 did not change systematically throughout a given trial.