Nasal nitric oxide is increased in allergic rhinitis

Background Nitric oxide (NO) plays a major role in the regulation of vascular tone and in non-specific host defence. The epithelium in the paranasal sinuses was recently identified as the major site of NO production in the upper airways. Objective To investigate NO status in allergic rhinitis, we compared the NO concentration in the nasal cavities of control subjects (n= 19) and in patients with allergic rhinitis (n= 36) with symptoms (WS, n= 17) or without symptoms (WOS, n= 19) on the day of the test. Methods NO concentration was measured using a chemiluminescent analyser aspiring from each nasal cavity at a sampling flow rate of 0.7L/min, before and 10min after administration of a nasal vasoconstrictor. Results The mean NO concentration (± se) in the control was 235 ± 11 ppb and 225 ± 9 ppb in the right and left nostrils respectively, and was decreased by 14% and 12% by the nasal vasoconstrictor (P < 0.001). The NO concentration in patients with allergic rhinitis was significantly higher in the right and left nostrils (382 × 20 ppb and 396 ± 28 respectively, P < 0.0001 versus control). All WOS patients demonstrated normal or increased NO concentrations in both nostrils, whereas two WS patients showed decreased NO concentrations in the left nostril. Inhalation of a nasal vasoconstrictor increased NO concentration by 6% and 27% in the right and left nostrils respectively in WS patients. Conclusion Nasal NO concentration is increased in patients with allergic rhinitis. Interestingly, patients without symptoms on the day of the test also showed a clear-cut increase in nasal NO production, which could reflect a permanent inflammation of the sinus mucosa.