Airborne nitric oxide: Inflammatory marker and aerocrine messenger in man

TL;DRAbstract

1. In healthy subjects, exhaled NO originates mainly from the upper airways with only a minor contribution from the lower airways and the lungs. A large NO production takes place in the epithelium of the paranasal sinuses and this NO contributes considerably to the levels of NO found in nasally exhaled air. Immunohistochemical and mRNA in situ hybridisation studies suggest that sinus NO synthase is identical or very closely related to the human iNOS. Furthermore, the NOS activity in sinus mucosa is mostly Ca(2+)-independent. However, the regulation of sinus NOS expression seems to differ fundamentally from what has earlier been described for iNOS. Thus, sinus NOS is constitutively expressed and seems resistant to steroids. The high local NO concentrations in the nasal airways and the sinuses may help to protect against airborne infectious agents. Thus, airborne NO may represent the very first line of defence in the airways, possibly acting on pathogens even before they reach the mucosa

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