N-omega-nitro-L-arginine methyl ester increases airway responsiveness to serotonin but not to acetylcholine in cats in vivo.

BACKGROUND We previously reported that N(omega)-nitro-L-arginine methyl ester (L-NAME) enhances airway responsiveness to inhaled serotonin in cats treated with atropine and propranolol. OBJECTIVE To further elucidate the role of nitric oxide (NO) in airway responsiveness, we investigated whether L-NAME induces airway hyperresponsiveness to serotonin and acetylcholine (ACh) in animals with intact innervation. METHODS Cats were anesthetized with pentobarbital sodium (50 mg/kg, i.p.), and mechanically ventilated. To assess airway responsiveness, we measured increase in total pulmonary resistance (RL) produced by delivering serotonin or ACh aerosol to the airway, and determined PC200 (the concentration which caused a 200% increase in RL). RESULTS The following results were obtained: (1) Airway responsiveness to serotonin was significantly enhanced by the administration of L-NAME (100 mg/kg) in animals treated with atropine and propranolol. (2) Airway responsiveness to serotonin was also significantly enhanced by L- NAME in animals with intact innervation. (3) In contrast, airway responsiveness to ACh was not changed by the addition of L-NAME in cats with intact innervation. CONCLUSION These results suggest that NO modulates nonspecific airway responsiveness in animals with intact innervation, presumably by a reflex mechanism.