Objectives: Histamine is an important chemical mediator in both nasal and bronchial inflammation in patients with allergic rhinitis and asthma. The effect of histamine receptor-1 antagonists on nasal mucosa in vivo is well known, however, the effect on tracheal smooth muscle has rarely been explored. The purpose of this study was to determine the effects of fexofenadine on isolated tracheal smooth muscle in vitro. Methods: Six tracheal strips were used for each experiment, and one untreated strip served as a control. We examined the effectiveness of fexofenadine on isolated rat tracheal smooth muscle by testing the effect on: 1) tracheal smooth muscle resting tension; 2) contraction caused by 10-6 M methacholine as a parasympathetic mimetic; and 3) electrically induced tracheal smooth muscle contractions. Results: The results indicated that addition of methacholine caused the trachea to contract in a dose-dependent manner. The addition of fexofenadine at a dose of 10-4 M elicited a significant relaxation response compared to 10-6 M methacholine-induced contraction. There were no detectable changes in the peak tension of electrical field stimulation-induced contractions in the fexofenadine group. Conclusion: High concentrations of fexofenadine had an anti-cholinergic effect. In addition to diminishing histamine-mediated allergic symptoms, fexofenadine may have a potentially therapeutic implication in alleviating asthma-related symptoms due to reducing methacholine-induced contractions of tracheal smooth muscle though these aspects were not studied.
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