Noninvasive Method to Measure Airway Obstruction in Nonanesthetized Allergen-Sensitized and Challenged Mice

Abstract

Background: Conventional methods used to measure bronchoconstriction are invasive, technically demanding and time consuming. Objectives: Our purpose was to evaluate a noninvasive method, by barometric whole-body plethysmography (WBP), to evaluate bronchoconstriction and bronchial hyperreactivity in mice induced by ovalbumin (OA) inhalation challenge in comparison with an invasive method. Enhanced pause (P_enh) was used as an index of airway obstruction. Methods: Eight mice were sensitized by OA (group I) and then challenged with OA. Twenty-four hours later, pulmonary function testing (PFT) was measured by WBP at baseline and after a methacholine (MCh) inhalation challenge. Eight weight-matched normal mice served as controls (group II). Four hours after PFT in a nonanesthetized condition, all animals were anesthetized and paralyzed. Baseline PFT was performed by the maximal forced expiratory maneuver (MFEM), and then the animals were given varying doses of acetylcholine (ACh; 25, 50, 75, 100 µg/kg) injected through the jugular vein. Five seconds after ACh injections, pulmonary functions were examined, including MFEM, peak airway pressure and total lung compliance. After completing PFT, bronchoalveolar lavage (BAL) was performed, the animals were sacrificed, and the lungs were examined histologically. Results: Group I had increased P_enh in response to MCh in the nonanesthetized condition and decreased flow in the anesthetized condition, characterized by greater decreases in MFEM flow rates MFEF 50% and MFEF 25% than the control group. The peak flows, MFEF 75%, MFEF 50% and MFEF 25%, for group I were lower than those for group II at doses of ACh higher than 25 µg/kg. There were concentration-dependent increases in P_enh in response to aerosolized MCh in both groups, but the P_enh in response to aerosolized MCh was significantly enhanced in group I when compared with controls. The doses of MCh required for 100% increases in P_enh were significantly reduced for sensitized and challenged mice. There was a positive correlation between provocative doses PD200 P_enh MCh, PD20 MFEF 50% ACh and PD20 MFEF 25% ACh. There was a negative correlation between the PD200 P_enh MCh and the percentage of eosinophils in BAL fluid. There was an increased total cell count and an increased percentage and absolute number of eosinophils and lymphocytes in the BAL fluid of sensitized animals. OA-sensitized mice also had a severe inflammatory reaction of airway and lung tissue, characterized by congestion, edema and inflammatory cell infiltration and desquamation of bronchial epithelial cells. Conclusion: The noninvasive method of WBP can be used to evaluate airway obstruction and hyperreactivity induced in mice by allergen challenge.