Repeated aeroallergen challenge induces lung dysfunction but not bronchial hyperresponsiveness in conscious guinea pigs.

Adult male Hartley-strain guinea pigs were sensitized by 10 min exposure to aerosolized 1% ovalbumin (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion). One week after sensitization, animals were placed in an exposure chamber and challenged (nebulized OA 0.5%) until each animal showed labored breathing. Maximal exposure time was 10 min. Diphenhydramine (20 mg/kg, i.p.) was given 1 h before each OA challenge to protect the animals from bronchospasmic death. Antigen challenge was repeated twice a week for 2 weeks. The specific airway resistance (sR(aw)) changes in response to increasing concentrations of aerosolized acetylcholine (Ach) were determined. The data obtained in this study demonstrated that repeated antigen challenge produced a significant bronchial tone i.e. an increase in sR(aw) and a decline in specific airway conductance (sG(aw)) and failed to induce bronchial hyperreactivity to aerosolized acetylcholine (Ach) in conscious guinea pigs.