Inhaled mannitol shifts exhaled nitric oxide in opposite directions in asthmatics and healthy subjects

We investigated if healthy subjects could release NO upon hyperosmolar challenge as a defence mechanism, and whether asthmatics with atopy showed an altered response. A plot Of NO output versus ROW rate was used to calculate the alveolar level and the NO-flux from the airways. The asthmatics had a higher NO output and this was: due to an increased NO-flux from the airways, 86 +/- 30 nl min(-1) compared with control 21 +/- nl min(-1) (P < 0.05). The alveolar NO levels showed no difference. In response to a dry powder of mannitol the exhaled NO concentration decreased in asthmatics by 37 +/- 7%, but increased in the control by 9 +/- 4% (P < 0.001). The FEV1.0 decreased 13 +/- 2% and airway conductance 42 +/- 7% in asthmatics and in the controls 2 +/- 1% and 0 +/- 7%, respectively (P < 0.001). We conclude that asthmatics have an altered response to mannitol challenge in regards to exhaled NO. This may result from down regulation of constitutive NO production as a result of high levels of NO flux from the airways. (C) 2001 Elsevier Science B.V. All rights reserved.