Acute topical steroid administration blocks mast cell increase and the late asthmatic response of the canine peripheral airways

Previous studies indicated that mast cell number increased after airway exposure to Ascaris suum antigen (Ag). The following two series of experiments were performed to test the hypothesis that this phenomenon may be associated with the Ag-induced late-phase bronchoconstriction (LAR). In the first, two bronchoscopies wedged in airway segments of two contralateral lobes of 16 dogs were used to deliver 0.26, 2.6, or 26 μg of Ag to one lobe; the other served as a control. After the observation of a LAR, Ag and control lobes plus one unexposed tissue sample were collected and prepared for histologic examination. The data showed that the incidence, time of onset, and magnitude of the LAR were dose-related. In the second series of experiments, performed in 14 dogs, the tracheal mucosal surface was surgically exposed to allow 80 μg of beclomethasone dipropionate to be sprayed on one half while the other half was left untreated. Pledgets saturated with 0.2 μg of Ag were placed on both sides 1 h later. Then two bronchoscopes were used to pretreat airways of two contralateral lobes to 40 μg of either the steroid or the vehicle. One hour later, both airways were exposed to 2.6 μg of aerosolized Ag. Of these 14 dogs monitored for peripheral airway responses, seven demonstrated a LAR in the vehicle-treated airway. In all seven dogs, the LAR was absent in the steroid-treated airway even though the cellular profiles of the two airways did not significantly differ. In seven additional dogs, the bronchoscopic procedure was performed as previously described. However, these dogs were killed 1 h after Ag exposure. Steroid pretreatment significantly attenuated the acute response to Ag by an average of 35% in the 21 dogs tested. In the trachea, steroid pretreatment prevented the Ag-induced mast cell increase that was observed in the untreated tissue. In the seven dogs killed 1 h after Ag exposure, the number of mast cells was significantly greater in the vehicle-treated airway at that time than in the steroid-treated airway. The results from this series of experiments suggest that acute topical steroid administration can attenuate the immediate physiologic and mast cell response to Ag and block the LAR.