Selective phosphodiesterase inhibitors modulate the activity of alveolar macrophages from sensitized guinea-pigs

The aim of this study was to investigate the effects of selective phosphodiesterase (PDE)3 and PDE4 inhibitors on arachidonate release by alveolar macrophages from sensitized and challenged guinea-pigs. Guinea-pigs were sensitized and challenged with ovalbumin administered by aerosol. Bronchoalveolar lavage was performed 48 h later and the PDE and cyclic adenosine monophosphate (cAMP) contents of or the arachidonate release from alveolar macrophages, stimulated in vitro with N-formyl-Met-Leu-Phe (fMLP), were evaluated. PDE3 and PDE4 activities were detected in preparations of macrophage lysate from sensitized challenged and sensitized control animals. Oral pretreatment, prior to antigen challenge in sensitized guinea-pigs, with rolipram or Ro 20-1724 (PDE4 inhibitors) but not milrinone (PDE3 inhibitor) significantly reduced the arachidonate release from alveolar macrophages. In vitro incubation of alveolar macrophages from challenged guinea-pigs with Ro 20-1724 or the cAMP analogue dibutyryl cAMP (db-cAMP) but not milrinone or the cyclic guanosine monophosphate (cGMP) analogue 8-bromo-cGMP (8-br-cGMP) significantly reduced arachidonate release. Incubation of the cells with a combination of milrinone plus rolipram or Ro 20-1724 elicited a marked and significant reduction in arachidonate release by alveolar macrophages stimulated with fMLP. In conclusion, these data show that phosphodiesterase-4 isoenzyme may regulate the release of inflammatory mediators such as arachidonate from macrophages through an increase in intracellular cyclic adenosine monophosphate. This suggests that phosphodiesterase-4 inhibitors have potential in the treatment of inflammatory disorders of the lung.