Nitric oxide is a mediator of the late-phase response in an animal model of nasal allergy

The presence of nitric oxide (NO) in the nose is well documented; however, the role of this molecule in nasal physiology is still poorly understood. O ur laboratory has previously demonstrated that NO is a mediator of the imme diate secretory response to an intranasal histamine challenge in a rat mode l of nasal allergy. Histamine challenge, however, does not elicit a late-ph ase response (LPR). To study the role of NO in the LPR, we developed a mode l of nasal allergy in which brown Norway rats are actively sensitized to th e allergen ovalbumin and later challenged intranasally with either phosphat e-buffered saline solution (vehicle), ovalbumin in vehicle, or ovalbumin an d the NO synthase inhibitor N-nitro-L-arginine methyl ester. In each experi ment, nasal lavage samples were collected 30, 120, 240, and 360 minutes aft er challenge. Lavage samples were analyzed for albumin content by ELISA, in flammatory cell concentration with a hemocytometer, and evidence of inflamm ation by light microscopy. Blocking NO synthesis with N-nitro-L-arginine me thyl ester significantly inhibited both albumin exudation and inflammatory cell influx into the nasal cavity during the LPR. These data suggest that N O plays a role in the LPR of nasal allergy.