Maximal forced expiratory maneuver to measure airway obstruction in anesthetized guinea pigs

Our purpose was to develop a method using a maximal forced expiratory flow (MFEF) for the study of airway hyperreactivity in guinea pigs induced by ovalbumin inhalation challenge. Eight guinea pigs (weight range 350-450 g) were sensitized by inhaled ovalbumin (group I) 2 times during a 1-week interval and then subjected to provocation with ovalbumin 1 week later. Pulmonary function tests at baseline and after acetylcholine challenge were performed 72 h later. Eight weight-matched normal guinea pigs served as controls (group II). All animals were anesthetized, paralyzed with gallamine, and ventilated via tracheostomy. They were given varying doses of acetylcholine (25, 50, 75, 100 micrograms/kg) injected through a jugular venous catheter. Five seconds after acetylcholine injections, pulmonary function was examined, including maximal forced expiratory maneuver, peak airway pressure (PaO) and total lung compliance. After completing the pulmonary function tests, bronchoalveolar lavage (BAL) was performed with 20 ml normal saline divided into two doses. Thereafter, the lungs were removed and examined histologically. The results showed that guinea pigs treated with ovalbumin had worse pulmonary function tests than normal controls, characterized by lower peak flow, MFEF 75%, MFEF 50% and vital capacity. The ovalbumin-presensitized guinea pigs also demonstrated severe bronchoconstriction in response to acetylcholine, characterized by larger decreases in peak flow, MFEF 75%, MFEF 50% and in vital capacity than the control group. Total cell count, the percentage and absolute number of eosinophils and lymphocytes were increased, and the percentage of macrophages was decreased in the BAL fluid of these animals. Finally, ovalbumin-sensitized guinea pigs had a severe inflammatory reaction in airway and lung tissue, characterized by congestion, edema and inflammatory cell infiltration (especially lymphocytes and eosinophils) and desquamation of bronchial epithelial cells. In conclusion, a forced expiratory maneuver can be used to perform pulmonary function tests in guinea pigs.