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In cystic fibrosis (CF), low concentrations of exhaled nitric oxide (NO) and reduced expression of inducible nitric oxide synthase (iNOS) in airway epithelium have been reported. However, abundant iNOS expression has been found in the subepithelial tissues and elevated concentrations of NO metabolites in breath condensate and sputum. These conflicting results may be explained by increased scavenging of NO by superoxide radicals, resulting in rapid conversion to peroxynitrite, so that only a small proportion of the NO produced in the lung tissue reaches the airway lumen. If iNOS were active in the CF lung, exhaled NO would be further reduced by glucocorticoid treatment.CF patients (n=13) were recruited to a double-blind, placebo-controlled study with crossover. Treatment comprised prednisolone or placebo for 5 days with a 9 day washout. After each treatment, exhaled NO was measured, spirometry performed and blood collected for measurement of serum nitrogen dioxide/nitrous oxide (NO2/NO3).Ten patients (8 male) completed the study. Following prednisolone treatment (mean±sd) exhaled NO concentration (3.1±1.6 parts per billion (ppb)) was significantly reducedversusplacebo treatment (4.9±4.2 ppb; p2/NO3concentration were unchanged.These findings support the hypothesis that glucocorticoids suppress nitric oxide production in cystic fibrosis airways by reducing inducible nitric oxide synthase expression or by inhibiting recruitment of neutrophils, cells which express inducible nitric oxide synthase.

To the Editors: In a recent issue of the European Respiratory Journal , Tanaka et al. 1 studied polymorphisms in the tumour necrosis factor (TNF) and lymphotoxin A genes with respect to their effect on lung function of smokers, and failed to find any association with chronic obstructive pulmonary disease (COPD) phenotypes. Tanaka et al. 1 acknowledge that their work is not a true case–control study, but that it would be better described as an investigation of genetic contribution to disease severity. There have been several studies of variation in TNF with respect to susceptibility to COPD, although many of these have used relatively small sample sizes and are therefore underpowered, and so are likely to lead to results that cannot be replicated. As part of a European Union collaborative project, we have …