Microvascular Leakage in the Airway Wall and Lumen During Allergen Induced Early and Late Responses in Rats

The potential contribution of microvascular leakage to airway narrowing during the early (ER) and late (LR) responses following allergen challenge was determined in Brown Norway (BN) rats actively sensitized with ovalbumin (OA). To study leak into the airway wall, rats (n=46) were challenged 2 weeks later with aerosolized OA, saline, or serotonin (5-HT) to study either ER (n=25), LR (n=15), or 5-HT (n=6) responses. Pulmonary resistance (RL) was used to measure airway narrowing. Microvascular leak was determined by the Evans blue (EB) technique in the airway tissues, and in another group of BN, by EB in bronchoalveolar lavage (BAL) in the airway lumen (n=43). EB increased in the airways of 5-HT challenged rats (P<0.05), but not during ER or LR. EB in BAL increased significantly during the ER (101±31.35 ng/ml BAL), vs saline challenge (10.82±1.66;P<0.05) and during the LR at 3, 4, 5, and 7 h following OA challenge compared with controls (P<0.05). These results suggest that fluid transits rapidly from the airway microvascular circulation and into the airway lumen following allergen challenge. The measurement of EB in BAL can detect microvascular leak into the airway lumen during the ER and LR. Plasma leak into the airway lumen may contribute to the increase in pulmonary resistance observed during ER and LR in BN rats.