Relationship between airway sensitivity to adenosine 5 ' monophosphate andthe shape of the concentration-response curve to methacholine in subjects with allergic rhinitis

The objective of this study was to determine differences in airway sensitiv ity to adenosine 5'-monophosphate (AMP) between allergic rhinitis subjects with plateau and those without evidence of plateau on the concentration-res ponse curves to methacholine. A total of 51 adults (38 subjects with allergic rhinitis and 13 healthy con trols) were challenged with increasing concentrations of methacholine and A MP. The methacholine challenge was terminated when there was a 40% or more decrease in forced expiratory volume in 1 sec (FEV1), whereas the AMP chall enge was stopped when FEV1 had fallen by more than 20%. A plateau for methacholine was detected in all 13 healthy controls and in 2 7 patients with allergic rhinitis (AR-plateau group), whereas 11 subjects w ith allergic rhinitis did not exhibit a plateau (AR-non-plateau group). The median (range) PC20 AMP (provocative concentration required to produce a 2 0% 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(-1) in the healthy control group (P=0.007). The p roportion 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 s ensitivity to methacholine and plateau showed bronchoconstriction in respon se to AMP. We conclude that, in subjects with allergic rhinitis, the absence of platea u on the concentration-response curves to methacholine is associated with a higher prevalence and degree of bronchoconstriction in response to AMP. Ho wever, the two bronchoconstrictor stimuli were not identifying the same abn ormalities of the airways.