Effect of Fluticasone on Airway Smooth Muscle (ASM) in Mice Treated with IL-13

RATIONALE: Fluticasone has an effect on airway hyperresponsiveness (AHR) and enhances bronchodilatation and broncho-protection. The cytokine IL-13 plays an important role in inducing features of asthma including AHR. The purpose for this study was to determine the effect of fluticasone on contractility and relaxation of ASM treated with IL-13.METHODS: Balb/c mice were treated with fluticasone, 33 μg/ml nebulized for 10 min, for two consecutive days in vivo. Mice were sacrificed and the tracheas incubated with 10 μg/ml IL-13 in vitro for 24 hrs at 4°C. Tracheal rings were suspended in a muscle bath containing Krebs buffer, gassed with 95% O2 - 5% CO2 at pH 7.4. Contraction to KCl, concentration-response contraction curves to acetylcholine (Ach), and isoproterenol (Iso) concentration-response relaxation curves were then generated in vitro.RESULTS: IL-13 treatment did not increase Ach contraction in vitro. Fluticasone+IL-13 caused a modest, non-significant decrease in Ach contraction compared to IL-13 alone. Ach contraction after fluticasone alone was not different from that after fluticasone+IL-13. In untreated ASM Iso caused approximately 50% of maximal relaxation. However, after treatment with IL-13, the relaxation to Iso was significantly diminished. Relaxation to Iso after fluticasone alone was not significantly different from untreated controls. Iso relaxation after Fluticasone+IL-13 was reduced to the same extent as after IL-13 alone.CONCLUSIONS: IL-13 significantly inhibits the relaxation response to Iso in vitro and the diminished response to Iso was not restored by fluticasone. RATIONALE: Fluticasone has an effect on airway hyperresponsiveness (AHR) and enhances bronchodilatation and broncho-protection. The cytokine IL-13 plays an important role in inducing features of asthma including AHR. The purpose for this study was to determine the effect of fluticasone on contractility and relaxation of ASM treated with IL-13. METHODS: Balb/c mice were treated with fluticasone, 33 μg/ml nebulized for 10 min, for two consecutive days in vivo. Mice were sacrificed and the tracheas incubated with 10 μg/ml IL-13 in vitro for 24 hrs at 4°C. Tracheal rings were suspended in a muscle bath containing Krebs buffer, gassed with 95% O2 - 5% CO2 at pH 7.4. Contraction to KCl, concentration-response contraction curves to acetylcholine (Ach), and isoproterenol (Iso) concentration-response relaxation curves were then generated in vitro. RESULTS: IL-13 treatment did not increase Ach contraction in vitro. Fluticasone+IL-13 caused a modest, non-significant decrease in Ach contraction compared to IL-13 alone. Ach contraction after fluticasone alone was not different from that after fluticasone+IL-13. In untreated ASM Iso caused approximately 50% of maximal relaxation. However, after treatment with IL-13, the relaxation to Iso was significantly diminished. Relaxation to Iso after fluticasone alone was not significantly different from untreated controls. Iso relaxation after Fluticasone+IL-13 was reduced to the same extent as after IL-13 alone. CONCLUSIONS: IL-13 significantly inhibits the relaxation response to Iso in vitro and the diminished response to Iso was not restored by fluticasone.