Evaluation of the respiratory allergenicity of a fire-extinguisher powder in a rat model of allergic asthma

Male 8/9-week-old Brown Norway rats were given s. c. either a fire-extinguischer powder (FEP; siliconezed powder on ammonium phosphate / ammonium sulfate basis), ovalbumin (OA) plus alum, or vehicle on days 0,2 and 7 to induce hypersensitivity. An antigen challenge was performed under anesthesia on day 14 or 21, respectively, during simultaneous recording of lung function. The FEP-treated animals were challenged with either low or high FEP aerosol dose, or they were not challenged (negative control, NEG). The OA-sensitized animals were challenged with OA aerosol (POS). The vehicle-treated group was exposed to the high FEP aerosol dose to assess non-specific reactivity(NFEP). A novel dose control system was used which processes data on respiratory minute volume and aerosol concentration. Airway hyperreactivity was assessed 22-24 h after OA challenge. Brochoalveolar lavage (BAL) was performed and blood withdrawn for IgE analysis 44-48 h after challenge. At both time points (14/21 days), the early reaction after OA aerosol challenge was determined as a marked increase in airway resistance, and a marked hyperreactivity was found in the OA vs. NEG animanls 24 h after challenge. In the FEP groups as well in the NFEP group only a moderate increase in resistance and a slight to moderate hyperreactivity were detected. Significant eosinophilia was only detected in the POS group. We conclude: the tested FEP did not induce respiratory allergenicity but moderate non-specific airway reactions in a rat model of allergic asthma.