Respiratory pulmonary mechanics in chronically challenged mice. Changes in total lung resistance to increasing doses of aerosolized methacholine expressed as percent increase in RL above postsaline values (A,D). Values for methacholine PC₂₀₀ (B,E) and slope (C,F) were determined for each dose-response curve. Selected groups of mice were administered (A-C) dexamethasone (2 mg/kg intraperitoneally thrice weekly before each day of exposure) or (D-F) busulfan (25 mg/kg intraperitoneally once fortnightly). Each point or bar represents the mean and vertical lines the standard error of the mean. Values in parentheses indicate number of animals per group. *P < .05 and **P < .01 between selected groups.