Relationship between airway sensitivity to adenosine 5′ monophosphate and the shape of the concentration–response curve to methacholine in subjects with allergic rhinitis

Abstract

The objective of this study was to determine differences in airway sensitivity to adenosine 5′-monophosphate (AMP) between allergic rhinitis subjects with plateau and those without evidence of plateau on the concentration–response curves to methacholine.A total of 51 adults (38 subjects with allergic rhinitis and 13 healthy controls) were challenged with increasing concentrations of methacholine and AMP. The methacholine challenge was terminated when there was a 40% or more decrease in forced expiratory volume in 1 sec (FEV1), whereas the AMP challenge was stopped when FEV1had fallen by more than 20%.A plateau for methacholine was detected in all 13 healthy controls and in 27 patients with allergic rhinitis (AR-plateau group), whereas 11 subjects with allergic rhinitis did not exhibit a plateau (AR-non-plateau group). The median (range) PC20AMP (provocative concentration required to produce a 20% fall in FEV1) value for the AR-non-plateau group was 44·0 mg ml−1(3·3–400·0), compared with 400·0 mg ml−1(12·1–400·0) in the AR-plateau group (P=0·03) and 400·0 mg ml−1in the healthy control group (P=0·007). The proportion of subjects who showed bronchoconstriction in response to AMP was higher in the AR-non-plateau group (73%) than in the AR-plateau group (30%) (P=0·03). However, three subjects with allergic rhinitis who had normal sensitivity to methacholine and plateau showed bronchoconstriction in response to AMP.We conclude that, in subjects with allergic rhinitis, the absence of plateau on the concentration–response curves to methacholine is associated with a higher prevalence and degree of bronchoconstriction in response to AMP. However, the two bronchoconstrictor stimuli were not identifying the same abnormalities of the airways.