Effect of dexamethasone and endogenous corticosterone on airway hyperresponsiveness and eosinophilia in the mouse

Open Access
Publisher Website
Google Scholar
Abstract
1 Mice were sensitized by 7 intraperitoneal injections of ovalbumin without adjuvant (10 μg in 0.5 ml of sterile saline) on alternate days and after 3 weeks exposed to either ovalbumin (2 mg ml−1 in sterile saline) or saline aerosol for 5 min on 8 consecutive days. One day before the first challenge, animals were injected intraperitoneally on a daily basis with vehicle (0.25 ml sterile saline), dexamethasone (0.5 mg kg−1) or metyrapone (30 mg kg−1). 2 In vehicle-treated ovalbumin-sensitized animals ovalbumin challenge induced a significant increase of airway responsiveness to metacholine both in vitro (27%, P < 0.05) and in vivo (40%, P < 0.05) compared to saline-challenged mice. Virtually no eosinophils could be detected after saline challenge, whereas the numbers of eosinophils were significantly increased (P < 0.01) at both 3 and 24 h after the last ovalbumin challenge (5.48 ± 3.8 × 103 and 9.13 ± 1.7 × 103 cells, respectively). Furthermore, a significant increase in ovalbumin-specific immunoglobulin E level (583 ± 103 units ml−1, P < 0.05) was observed after ovalbumin challenge compared to saline challenge (201 ± 38 units ml−1). 3 Plasma corticosterone level was significantly reduced (−92%, P < 0.001) after treatment with metyrapone. Treatment with metyrapone significantly increased eosinophil infiltration (17.4 ± 9.93 × 103 and 18.7 ± 2.57 × 103 cells, P < 0.05 at 3 h and 24 h, respectively) and potentiated airway hyperresponsiveness to methacholine compared to vehicle-treated ovalbumin-challenged animals. Dexamethasone inhibited both in vitro and in vivo hyperresponsiveness as well as antigen-induced infiltration of eosinophils (0, P < 0.05 and 0.7 ± 0.33 × 103 cells, P < 0.05 at 3 h and 24 h, respectively). Metyrapone as well as dexamethasone did not affect the increase in ovalbumin-specific immunoglobulin E levels after ovalbumin challenge (565 ± 70 units/ml−1; P < 0.05; 552 ± 48 units ml−1, P < 0.05 respectively). 4 From these data it can be concluded that exogenously applied corticosteroids can inhibit eosinophil infiltration as well as airway hyperresponsiveness. Vise versa, endogenously produced corticosteroids play a down-regulating role on the induction of both eosinophil infiltration and airway hyperresponsiveness.