Allergen-induced airway obstruction in guinea-pigs is associated with changes in nitric oxide levels in exhaled air.

Endogenously produced nitric oxide (NO) was monitored in exhaled air from ovalbumin-sensitized and pentobarbital anaesthetized guinea-pigs. Stable levels of nitric oxide were detected in exhaled air over a 30-min control period in each experiment (9.2 +/- 1.4 parts per billion, [ppb]). Insufflation pressure and NO in exhaled air immediately increased, in a dose dependent manner, in response to challenge with nebulized allergen (Ovalbumin, 0.1-10 mg). Indomethacin (5 mg kg-1) augmented the allergen-induced increases in insufflation pressure and NO. Fifteen min after the challenge the insufflation pressure remained elevated while NO in exhaled air had dropped below control levels. The increase in insufflation pressure induced by inhalation of PGF2 alpha (5 micrograms) was accompanied by an increase in nitric oxide in exhaled air, which however was significantly less than the increase in NO induced by allergen challenge. The results suggest a role for NO mechanisms in asthma.