Natural Pollen Exposure Increases the Response Plateau to Adenosine 5'-Monophosphate and Bronchial but Not Alveolar Nitric Oxide in Sensitized Subjects

Background: The effect of allergen exposure on airway responsiveness and exhaled nitric oxide (NO) has been well documented, but no information is available on allergen-induced changes in the response plateau to adenosine 5′-monophosphate (AMP) and in bronchial NO flux (J'aw NO ) and alveolar NO (CA NO ). Objectives: To determine the effect of natural allergen exposure, a proinflammatory stimulus, on the shape of the concentration-response curve to AMP and NO production in airway and alveolar sites. Methods: Airway responsiveness to high concentrations of methacholine and AMP, J'aw NO and CA NO values were obtained in 31 subjects with pollen allergy and in 11 healthy controls. Subjects with pollen allergy were studied before and at the height of the pollen season whereas healthy controls were tested on one occasion only. Results: In the group with pollen allergy, natural pollen exposure increased J'aw NO (p = 0.03), but had no effect on CA NO (p = 0.12). In the 18 subjects with pollen allergy who showed a response plateau to AMP in at least one period, the response plateau to AMP increased from a mean of 13.4% (95% CI: 8.2-18.5) out of season to 22.5% (95% CI: 15.5-29.4, p = 0.004) during the pollen season. Similar results were obtained with methacholine. Compared with healthy controls, subjects with pollen allergy had a higher response plateau and higher J'aw NO values. Conclusions: These findings suggest that inflammatory changes induced by natural allergen exposure in sensitized subjects are predominantly located in the airways and associated with modifications in the shape of the concentration-response curve to direct and indirect agonists.