Determination of airway hyperresponsiveness. Pulmonary function test were performed in sensitized and transnasally challenged mice. Mice were exposed to increasing doses of inhaled methacholine (Mch) and Penh values were registered. Allergic mice treated with 2,500 mcg of vit A developed a significantly decreased response to Mch when compared to allergic untreated controls. Values are expressed as mean ± SEM (n = 6 mice per group) for each Mch dose point. * p < 0,05.