Inhibition of allergen-induced lung eosinophilia by type-III and combined type III- and IV-selective phosphodiesterase inhibitors in Brown-Norway rats

We examined the effect of a type IV (rolipram) and a combined type III and IV (Org 20421) isoenzymeselective phosphodiesterase inhibitor upon allergeninduced pulmonary eosinophil recruitment in sensitised Brown Norway rats. Rats were sensitised with ovalbumin intraperitoneally and later challenged with ovalbumin aerosol which induced a significant increase in the total eosinophil and neutrophil count in bronchovalveolar lavage fluid at 24 hours (from 0.38 ± 0.12 to 1.36 ± 0.18 × 10⁶,p < 0.01 and from 0.06 ± 0.01 to 0.33 ± 0.07 × 10⁶,p < 0.01) respectively. Pretreatment with rolipram (30 µmol/kg) and Org 20421 (30 µmol/kg) abolished the eosinophilia and neutrophilia evoked by ovalbumin. We conclude that type IV and possibly type III isozyme phosphodiesterase inhibitors may regulate, directly or indirectly, eosinophil and neutrophil activity and/or those cells responsible for attracting them into the lung.