Effect of N omega-nitro-L-arginine on ventilatory response to hypercapnia in anesthetized cats

The effect of intravenous administration of 40 mg/kg N omega-nitro-L-arginine (L-NNA), an inhibitor of the synthesis of nitric oxide (NO), on the ventilatory response to CO2 was studied in anesthetized cats. The ventilatory response to CO2 was assessed during normoxia by applying square-wave changes in end-tidal PCO2 of approximately 1 kPa. Each CO2 response was separated into a fast peripheral and slow central component characterized by a CO2 sensitivity (Sp and Sc, respectively), time constant, time delay, and an offset (apneic threshold). L-NNA reduced Sp, Sc, and the apneic threshold significantly by approximately 30%. However, the ratio Sp/Sc was not changed. It is argued that the reduction in Sp and Sc, Sp/Sc remaining constant, may be due to a potent inhibitory action of L-NNA on the brain stem respiratory-integrating centers and on the neuromechanical link between these centers and respiratory movements. It is concluded that NO plays an important role in the control of breathing.