[Nitric oxide in the nose and paranasal sinuses--respiratory tract physiology in a new perspective].

Nitric oxide (NO) has important functions in a variety of physiological and pathophysiological processes in the body, including vasoregulation, haemostasis, neurotransmission, immunity and respiration. The discovery of surprisingly high concentrations of NO in the nasal airway and paranasal sinuses has important implications for the understanding of airway physiology. The high NO levels in the nasal and paranasal airways contribute to the first line defence against microorganisms. Furthermore, autoinhalation of nasal NO may improve pulmonary function and other remote physiological processes. This airborne messenger system represents a new physiological concept of potential clinical importance. However, NO, like several other mediators, has a dualistic function. Airway NO levels are increased in airway inflammations, such as asthma and allergic rhinitis, but is reduced in cystic fibrosis and other conditions with ciliary dysfunction, sinusitis and after exposure to tobacco and alcohol. Consequently, NO may prove valuable as a non-invasive marker in the diagnosis and monitoring of airway pathologies.