Allergen-induced changes in airway responsiveness are related to baseline airway responsiveness

In the literature, bronchial allergen challenge is usually reported to result in an increase in histamine-induced airway responsiveness (AR). The present study investigated the relation between baseline AR and allergen-induced changes in AR. The effect of allergen challenge on AR was investigated in 21 atopic asthmatic patients. Allergen challenge resulted in a significant decrease in PC₂₀ histamine after 24 h. When the group was divided into three subgroups according to baseline PC₂₀ histamine, a significant decrease in PC₂₀ histamine was found only in patients with relatively high baseline PC₂₀ histamine (groups 1 and 2). A significant inverse correlation was found between baseline PC₂₀ and allergen-induced PC₂₀ histamine. The effect of repeated allergen challenge on AR was studied in eight patients. The first allergen challenge resulted in a significant decrease in PC₂₀ histamine; no further decrease in mean PC₂₀ histamine was seen after the second allergen challenge. These results suggest that allergen-induced changes in AR occur mainly in patients with relatively high baseline PC₂₀ values. Once an increase in AR is induced, further allergen challenge does not always result in further increase in AR.