REPRODUCIBILITY OF ALLERGEN-INDUCED ASTHMA AND ASSOCIATED INCREASE INBRONCHIAL RESPONSIVENESS TO METHACHOLINE IN ASTHMATIC-CHILDREN

We studied the reproducibility of early (EAR) and late (LAR) asthmatic response to allergen challenge in 13 asthmatic children (four girls, age range: 10 to 17 years) sensitized only to Dermatophagoides pterony ssinus (Dp). Further, changes in bronchial responsiveness to inhaled m ethacholine following LAR were examined by measuring PC20FEV1 methacho line after 24, 48, and 72 hours. We carried out two carefully controll ed allergen challenges with the same allergen dose within 4 to 6 weeks , at least 3 weeks apart, in each subject. On each study day, a bronch ial challenge with methacholine was performed before and at different intervals after LAR. We found that EAR (maximal %fall in FEV1 within t he 1st hour) measured on two different days was highly reproducible (3 7.8% +/- 8.9 and 38.7% +/- 12.1; CR: 12.1; Ri: 0.92; CoV: 15.1). Late asthmatic response (maximal %fall in FEV1 between 2nd and 12th hour) w as also highly reproducible (47.5% +/- 12.4 and 46.1% +/- 13.4; CR: 10 .1; Ri: 0.96; CoV: 10.1). All patients showed increases in nonspecific bronchial responsiveness to methacholine after LAR. Geometric mean PC 20 M measured before the two allergen challenges was 0.609 mg/mL and 0 .620 mg/mL, respectively. These values significantly decreased 24, 48, and 72 hours after LAR (after 1st allergen challenge: 0.086, 0.116, a nd 0.295 mg/mL; after 2nd allergen challenge: 0.075, 0.141, and 0.263 mg/mL). Ratio changes in PC20 methacholine (pre-allergen PC20 methacho line/lowest postallergen PC20) were highly reproducible (Ri: 0.95). We concluded that bronchial response to allergen challenge and the assoc iated increase in responsiveness to methacholine are highly reproducib le in well selected asthmatic subjects. This experimental model seems to be a reliable method in the evaluation of antiallergic and antiasth matic drugs.