Dissimilarity between Seasonal Changes in Airway Responsiveness to Adenosine-5’-Monophosphate and Methacholine in Patients with Grass Pollen Allergic Rhinitis: Relation to Induced Sputum

Abstract

Background: In patients with allergic rhinitis, bronchial hyperresponsiveness (BHR) and airway inflammation may increase during pollen exposure. BHR can be assessed by adenosine-5′-monophosphate (AMP) or methacholine challenge. It has been suggested that BHR to AMP is more closely related to airway inflammation than BHR to methacholine. Seasonal allergic rhinitis offers a dynamic model to study changes in BHR and airway inflammation during natural allergen exposure. Methods: We measured BHR [provocative concentration causing a 20% fall (PC₂₀) in forced expiratory volume in 1 s (FEV₁)] to AMP and methacholine, and induced sputum cells in 16 rhinitis patients before and during the 2001 grass pollen season. Results: There was a decrease in PC₂₀ methacholine during pollen exposure (geometric mean PC₂₀ from 3.22 to 1.73 mg/ml, p = 0.0023), whereas no reduction was observed for PC₂₀ AMP (p = 0.11). There was no increase in sputum eosinophils [pre: 0.69% (95% confidence interval 0.22–2.07); during: 1.85 (0.55– 5.6), p = 0.31]. Although the correlation of log PC₂₀ methacholine and log PC₂₀ AMP at baseline was good (r = 0.76, p = 0.001), individual seasonal changes (doubling concentrations) in PC₂₀ methacholine were not correlated with changes in PC₂₀ AMP (ρ = 0.21, p = 0.44). There was no correlation between baseline log PC₂₀ methacholine or seasonal changes in PC₂₀ methacholine and sputum eosinophils (p > 0.12, all correlations). In contrast, there was a significant correlation between seasonal changes in PC₂₀ AMP and changes in sputum eosinophils (ρ = –0.59, p = 0.025). Conclusions: These data show dissimilarity between seasonal changes in PC₂₀ AMP and methacholine in patients with seasonal allergic rhinitis. Moreover, PC₂₀ AMP seems to be more closely related to sputum eosinophils than PC₂₀ methacholine. The clinical significance of this discrepancy is unclear.