The purpose of the present study was to assess the possible relationships between exhaled nitric oxide (ENO), a circulating marker of eosinophil activation, serum eosinophil cationic protein (SECP), level of airway responsiveness to methacholine and lung function in asthmatic children, as well as to compare these markers between children with and without inhaled steroid therapy. In a cross-sectional study ENO, SECP and bronchial hyperresponsiveness to methacholine were evaluated in a group of 57 asthmatic children (21 without and 36 with regulator inhaled steroid therapy; aged 6-13 yrs). ENO was significantly lower in steroid treated children (p<0.01). No significant differences between steroid treated and untreated children were observed for the provocative concentration of methacholine causing a 20\% fall in forced expiratory volume in one second (FEV1; PC20), SECP and FEV1. In the whole study population significant increase correlations were observed between PC20 and SECP (r=-0.329, p=0.013) and between ENO and FEV1\% of predicted (r=-0.348, p<0.01). In the group not receiving inhaled steroids the inverse relationship between PC20 and SECP was more evident (r=-0.581, p<0.001). In the steroid-treated group a significant inverse relationship was observed between ENO and FEV1 (r=-0.426, p=0.0011). The level of exhaled nitric oxide and the relationships between lung function, bronchial reactivity and markers of inflammation are different between steroid-treated and untreated asthmatic children. This has implications for the monitoring of asthma in childhood.
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