Nitric oxide (NO) is an important endogenous neurotransmitter and mediator. It participates in regulation of physiological processes in different organ systems including airways. Therefore, it is important to clarify its role in the regulation of both airway and vascular smooth muscle, neurotransmission and neurotoxicity, mucus transport, lung development and in the surfactant production. The bioactivity of NO is highly variable and depends on many factors: the presence and activity of NO-producing enzymes, activity of competitive enzymes (e.g. arginase), the amount of substrate for the NO production, the presence of reactive oxygen species and others. All of these can change NO primary physiological role into potentially harmful. The borderline between them is very fragile and in many cases not entirely clear. For this reason, the research focuses on a comprehensive understanding of NO synthesis and its metabolic pathways, genetic polymorphisms of NO synthesizing enzymes and related effects. Research is also motivated by frequent use of exhaled NO monitoring in the clinical manifestations of respiratory diseases. The review focuses on the latest knowledge about the production and function of this mediator and understanding the basic physiological processes in the airways.

FeNO measurement is a validated non-invasive technique, which is used for diagnosis and monitoring of asthma. It would be desirable to find a reliable method to monitor allergic rhinitis (AR) via measurement of FeNO, and/or nasal nitric oxide (nNO). The aim of our study was the assessment of the efficacy of FeNO and nNO as markers in AR treatment. FeNO and nNO were measured with the portable NO analyser (NIOX MINO®) in healthy participants and in patients with AR. The patients were examined during the pollen season and out of it. The effect of local corticosteroids and antihistamine therapy was observed in patients with AR during pollen season after three weeks of therapy. There are significant differences between FeNO and nNO in patients with AR compared to healthy controls at all set points of measurements. While FeNO responded well to the treatment with both antihistamines and combined therapy, nNO decreased only after combined therapy with antihistamines and nasal corticosteroids. nNO monitoring alone is not a suitable method to monitor inflammation of the upper airways in AR and its suppression by anti-allergic treatment and should be correlated with other markers as FeNO or symptom scores.

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Nitric oxide (NO) is an important endogenous mediator with significant role in the respiratory system. Many endogenous and exogenous factors influence the synthesis of NO and its level is significantly changed during the inflammation. Analysis of nasal nitric oxide (nNO) is not validated so far as the diagnostic method. There is a lack of reference values with possible identification of factors modulating the nNO levels. In healthy adult volunteers (n=141) we studied nasal NO values by NIOX MINO® (Aerocrine, Sweden) according to the recommendations of the ATS & ERS. Gender, age, height, body weight, waist-to-hip ratio, FEV1/FVC, PEF and numbers of leukocytes, eosinophils, basophils and monocytes were studied as potential variables influencing the levels of nNO. The complexity of the results allowed us to create a homogenous group for nasal NO monitoring and these data can be used further as the reference data for given variables. Because of significant correlation between nNO and exhaled NO, our results support the “one airway – one disease” concept. Reference values of nasal NO and emphasis of the individual parameters of tested young healthy population may serve as a starting point in the non-invasive monitoring of the upper airway inflammation.

ObjectiveExhaled nitric oxide has been proposed as a noninvasive marker of eosinophilic airway inflammation in lower airways. The aim of the study was to investigate the impact of atopy, pollen exposure, and pharmacological treatment on NO production in lower airways of patients with allergic rhinitis.Subjects and methodsMeasurements of exhaled NO were performed in 79 non-asthmatic subjects with seasonal allergic rhinitis outside and in pollen season, before and after pharmacological treatment, and in 54 healthy controls.ResultsPatients with allergic rhinitis had significantly higher levels of exhaled NO (18.3 ± 11.0 ppb) than healthy controls (13.0 ± 7.2 ppb) measured outside the pollen season (P = 0.0024). Increased exhaled NO levels were also found in patients with allergic rhinitis in the pollen season (27.0 ± 20.0 ppb) compared with the levels outside pollen season (P = 0.0001), before pharmacological treatment. In rhinitic patients treated by nasal corticosteroids and antihistamines in the pollen season, the levels of exhaled NO were significantly lower (17.0 ± 16.4 ppb; P = 0.045) than those before treatment. No difference was found in NO levels in rhinitic patients outside and in pollen season after pharmacological treatment.ConclusionsThis study has shown the presence of eosinophilic airway inflammation in the lower airways in allergic rhinitis patients. A significant increase of exhaled NO after pollen exposure in rhinitic patients underlies the impact of inflammation on the upper respiratory tract. A bidirectional link between upper and lower airways is confirmed by a decrease in exhaled NO in the pollen season, almost to the starting levels, after application of topic corticosteroids and antihistamines.