Study objectives: To determine the effect of cessation of exposure to pollen on airway responsiveness to adenosine 5′-monophosphate (AMP) in subjects with pollen-induced rhinitis, and to explore the relationship between changes in airway responsiveness and changes in exhaled nitric oxide (ENO) levels.
Study design: Subjects were studied during the pollen season and out of season.
Setting: Specialist allergy unit in a university hospital.
Patients: Fourteen subjects without asthma with pollen-induced rhinitis who showed bronchoconstriction in response to methacholine and AMP during the pollen season and 10 healthy nonatopic control subjects.
Measurements and results: In subjects with pollen-induced rhinitis, ENO concentrations, provocative concentration of agonist causing a 20% fall in FEV1 (PC20) methacholine, and PC20 AMP were determined during the pollen season and out of season. Healthy control subjects were studied during the pollen season. In subjects with allergic rhinitis, PC20 AMP increased from a geometric mean of 79.4 mg/mL (95% confidence interval [CI], 31.6 to 199.5 mg/mL) during the pollen season to 316.2 mg/mL (95% CI, 158.5 to 400.0 mg/mL) out of season (p = 0.004). The ENO concentrations decreased from 63.1 parts per billion (ppb) [95% CI, 50.1 to 79.4 ppb] during the pollen season to 30.2 ppb (95% CI, 23.4 to 38.0 ppb) out of season (p < 0.001). The ENO concentrations out of pollen season were still significantly increased in subjects with pollen-induced rhinitis when compared with healthy control subjects. There was no relationship between individual changes in ENO levels and changes in either PC20 methacholine or PC20 AMP.
Conclusions: In pollen-sensitive subjects with allergic rhinitis, the cessation of exposure to pollen is associated with a significant reduction of airway responsiveness to inhaled AMP. However, no association was found between allergen-induced changes in ENO values and in airway responsiveness to either direct or indirect bronchoconstrictors. These findings suggest that modifications in ENO and in airway responsiveness are the consequence of different alterations induced by allergen exposure on the lower airways.