Abstract: AimTo study cyclosporin A (CsA) aerosol for anti-airway hyperresponsiveness (AHR) in sensitized rats. MethodsSensitized Sprague-Dawley rats were given cyclosporin A (5, 20 g·L－1) and sodium cromoglycate (SCG, 20 g·L^-1) by aerosol (5 min per day), dexamethasone(DXM, 0.5 mg·kg^-1) i p once per day for 7 d before antigen challenge. The respiratory resistance（raw）and lung dynamic compliance（Cdyn）of the rats induced by methacholine (Mch) were measured 24 h after ovalbumin(OA) challenge. The PC50 changes of raw and PC25 changes of Cdyn were also investigated. ResultsPretreatment with CsA, sodium cromoglycate and dexamethasone inhibited the increase of raw and decrease of Cdyn caused by inhaling Mch. The value of raw PC50 in the CsA(5 g·L^-1) group 5.6 g·L^-1, the CsA(20 g·L^-1) group 6.4 g·L^-1, the SCG group 8.3 g·L^-1　and the DXM group 9.2 g·L^-1,　was significantly higher than that of the model group 1.9 g·L^-1 (P<0.05). The value of Cdyn PC25 in the CsA(5 g·L^-1) group 4.3 g·L^-1, the CsA(20 g·L^-1) group 5.4 g·L^-1, the SCG group 6.4 g·L^-1　and the DXM group 6.2 g·L^-1, was significantly higher than that of the model group 1.1　g·L^-1 (P<0.01). ConclusionAnti-AHR of CsA by aerosol in animal model offered an experimental evidence for topical inhalation of CsA in treatment of asthma.