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Nitric oxide (NO) is a mediator of vasodilatation and bronchodilatation synthesised from L-arginine by the enzyme NO synthase, which is either constitutive or induced by lipopolysaccharides and/or cytokines. The presence and function of NO synthase in normal or diseased lung is not yet clear.

Asthma is characterised by bronchial hyperresponsiveness, epithelial damage, inflammation, and increased cytokine production. To investigate the presence of NO synthase in asthma, we immunostained bronchial biopsies from non-steroid-treated people with asthma and non-asthmatic controls with specific polyvalent antisera to purified inducible NO synthase and to a selected peptide sequence of the same enzyme. Immunoreactivity was seen in the epithelium and some inflammatory cells in 22 of 23 biopsies from people with asthma, but in only 2 of 20 controls. To assess the relation of cytokines to NO synthase induction …