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We examined the effect of cessation of exposure to pollen on non-specific airway responsiveness in 10 grass and/or parietaria pollen sensitive asthmatics. Three methacholine inhalation challenges were performed, the first during pollen season (seasonal period), the second 2 months after the end of season (short lime after seasonal period), and the third 5 months after the end of season (long time after seasonal period). The dose-response curves to methacholine were characterized by the PC20 (provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. A maximal response plateau on the dose-response curve was considered to be present if three or more data points for FEV1 fell within a 5% response range. The challenge was stopped when FEV1 dropped more than 50% or the highest concentration of methacholine (200 mg/ml) was reached. The geometric mean (range) methacholine PC20 increased from 1.08 (0.18-37.22) in the seasonal period to 4.67 (0.71-200) mg/ml during the long time after seasonal period (P < 0.01). On the other hand, in six subjects in whom it was possible to obtain a plateau on at least one challenge, the level of the maximal response decreased from (mean ± s.e.m.) 44.1 ± 4.9 in the seasonal period to 30 ± 4.4 during the long time after seasonal period (P < 0.05). These results suggest that in pollen sensitive asthmatic patients, the cessation of exposure to pollen is associated with a reduction of non-specific bronchial responsiveness (PC20 and maximal degree of airway narrowing to methacholine). [ABSTRACT FROM AUTHOR]

Background Airway hyperresponsiveness to pharmacological agonists is a common feature in subjects with allergic rhinitis. Objective The aim of this study was to investigate differences in threshold value and shape of the concentration-response curves to methacholine between subjects with perennial allergic rhinitis and subjects with seasonal rhinitis. Methods We studied a sample of 72 non-asthmatic patients with allergic rhinitis. They were subdivided into two groups: subjects with only seasonal symptoms and skin sensitization to grass and/or Parietaria pollen allergens (seasonal group, n = 38), and subjects with perennial symptoms and skin sensitization to house dust mite, alone or with other allergens (perennial group, n = 34). They were challenged with methacholine (up to 200mg/mL), and concentration-response curves were characterized by the threshold value (PC20 = provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. The measurements in the seasonal group were done within the pollen season. Results The geometric mean methacholine PC20 for subjects of the perennial group was 6.9 mg/mL, compared with 23.4mg/mL in subjects of the seasonal group (P < 0.01). A plateau response was detected in 16 subjects of the perennial group and in 28 subjects of the seasonal group (P < 0.05). Moreover, the level of plateau was higher in subjects of the perennial group when compared with subjects of the seasonal group (23.8 ± 2.0% vs 19.2 ± 1.6%, P < 0.05). Conclusion In subjects with allergic rhinitis, sensitization to perennial allergens is associated not only with lower methacholine threshold values, but also with lower prevalence and higher level of plateau than sensitization to pollen allergens. [ABSTRACT FROM AUTHOR]