HIGH NITRIC-OXIDE PRODUCTION IN HUMAN PARANASAL SINUSES

Nitric oxide (NO) is present in air derived from the nasal airways. Ho wever, the precise origin and physiological role of airway-derived NO ale unknown. We report that NO in humans is produced by epithelial cel ls in the paranasal sinuses and is present in sinus air tn very high c oncentrations, close to the highest permissible atmospheric pollution levels. In immunohistochemical and mRNA in situ hybridization studies we show that an NO synthase most closely resembling the inducible isof orm is constitutively expressed apically in sinus epithelium. In contr ast, only weak NO synthase activity was found in the epithelium of the nasal cavity. Our findings, together with the well-known bacteriostat ic effects of NO, suggest a role for NO in the maintenance of sterilit y in the human paranasal sinuses.