Abstract
We aimed at investigating whether chronic allergen exposure (CAE) leads to the development of tolerance or enhances the airway hyperreactivity (AH) in sensitized rats. The airway resistance (Raw) was determined from the total respiratory system impedance under the control condition and following iv methacholine provocations (MCh 2-16 μg/kg) to establish the basal lung responsiveness. The rats were then sensitized to ovalbumin (OVA) and they were assigned into two groups: the rats in Group CAE (n=6) were exposed to aerosolized OVA three times a week throughout the study period, while the OVA was withdrawn during the entire protocol in the rats enrolled in Group A (n=8). Assessment of lung responsiveness was repeated in both groups in an identical manner on weeks 3, 6 and 9. The equivalent dose of MCh causing a 200% increase in Raw (ED200) was calculated from each challenge. OVA sensitization was proved to induce AH on week 3 in Groups CAE and A (decrease in ED200 of 33±14% and 40±7%, respectively). The subsequent OVA exposure affected significantly the MCh responsiveness with sustained decreases in ED200 on week 6 in Group A and gradual return to normal on week 9, whereas the ED200 in Group CAE was similar to the initial on weeks 6 and 9.
Our findings demonstrate a diminishment of AH following CAE suggesting its favourable influence on the reduction of an existing AH after allergic sensitization.
Supported by grant OTKA K81179.
- © 2011 ERS
