Fig. 6. The effect of salbutamol (A, 50 μg/ml; B, 100 μg/ml aerosol), roflumilast (1 mg/kg, i.p.), and codeine (10 mg/kg, i.p.) on the frequency of cough in response to citric acid (30 mM and 0.8 M) in guinea pigs (A) and rabbits (B), respectively, exposed to air or ozone (2 ppm, 30 minutes and 1 hour, respectively). The treatment an animal received at 7-day intervals was randomized to control for sequence effects. Animals were exposed to salbutamol (5 minutes) prior to citric acid challenge and to roflumilast or codeine before ozone exposure. Bars represent the mean, and vertical lines, S.E.M. (*P < 0.05, †P > 0.05, compared with ozone/vehicle group; for A and B, N = 32 and 16, respectively). The effect of roflumilast on pulmonary leukocyte recruitment in guinea pigs (C) and rabbits (D) following exposure to air or ozone. Animals were exposed to roflumilast (1 mg/kg, i.p.) before ozone exposure. Bars represent the mean, and vertical lines, S.E.M. (*P < 0.05 vs. ozone/vehicle group; guinea pig, N = 16; rabbit, N = 8). BALF, bronchoalveolar lavage fluid; MNL; mononuclear cells.