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) isoenzyme-selective phosphodiesterase inhibitor upon allergen-induced 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 x 10(6), p < 0.01 and from 0.06 +/- 0.01 to 0.33 +/- 0.07 x 10(6), p < 0.01) respectively. Pretreatment with rolipram (30 mumol/kg) and Org 20421 (30 mumol/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.