Effect of rolipram on airway hyperreactivity in chlorine-exposed mice. (A) Mice were exposed to a dose of 250 ppm-hour chlorine (8). The following day, respiratory mechanics were measured in anesthetized, mechanically ventilated mice at baseline and after inhalation of aerosolized methacholine using a FlexiVent system (SCIREQ, Montreal, PQ, Canada). The responses of chlorine-exposed and unexposed mice were significantly different (P < 0.05 by repeated measures ANOVA; n = 4 mice/group). (B) Mice were exposed to 256 ± 3 ppm-hour chlorine (mean ± SE, three exposures). Mice received rolipram (300 μg/kg) or vehicle intranasally 1 hour and then again 10–11 hours after exposure. The day after exposure, airway reactivity was measured as in A. The responses of rolipram- and vehicle-treated mice were significantly different (P < 0.05 by repeated measures ANOVA; n = 8–9 mice/group).