Comparison of arachidonic acid metabolism by pulmonary intravascular and alveolar macrophages exposed to particulate and soluble stimuli.

Pulmonary intravascular macrophages, as prominent components of the pulmonary mononuclear phagocyte system, could be significant mediators of lung inflammation. We have shown that intravascular and alveolar macrophages metabolize exogenous arachidonic acid to its inflammatory metabolites via the lipoxygenase and cyclooxygenase pathways after exposure to the calcium ionophore A23187. In this study, we compare the metabolism of endogenous arachidonic acid by porcine intravascular and alveolar macrophages after exposure to soluble and particulate stimuli. Since intravascular and alveolar macrophages are exposed to various stimuli in vivo, it is essential to know the range of inflammatory mediators that these cells can generate. Alveolar macrophages attached to plastic and exposed to the various stimuli produced prostaglandin F2 alpha, 12-hydroxyheptade-catrienoic acid (HHT), hydroxyeicosatetraenoic acids (HETE), and leukotriene B4. In contrast, adherent and stimulated intravascular macrophages produced several cyclooxygenase products and lipoxygenase products including 5-HETE, 12-HETE, and leukotriene B4. Both macrophages released large amounts of arachidonic acid upon exposure to each stimulant. Intravascular macrophages that were adherent to plastic or were stimulated with glass, asbestos, or A23187 released significantly (p less than 0.05) more metabolized arachidonic acid than similarly treated alveolar macrophages. The major cyclooxygenase metabolite released by alveolar macrophages was prostaglandin 2 alpha, whereas HHT was the primary metabolite of intravascular macrophages. The major lipoxygenase metabolite released by both macrophage types was 5-HETE, but intravascular macrophages also released substantial amounts of 12-HETE and leukotriene B4. In both macrophage preparations, lipoxygenase products composed most released metabolites. After exposure to iron, asbestos, and A23187 intravascular macrophages released significantly more (p less than 0.05) lipoxygenase metabolites than alveolar macrophages. However, in alveolar macrophages, chrysotile asbestos induced greater activity by the cyclooxygenase pathway than by the lipoxygenase pathway. Both asbestos and iron spheres induced release of arachidonic acid and its metabolites, but the most potent stimulants in both macrophage preparations were A23187, zymosan, and lipopolysaccharide. We conclude that stimulated intravascular macrophages use both cyclooxygenase and lipoxygenase pathways to metabolize endogenous arachidonic acid, that these macrophages are metabolically more active than alveolar macrophages, and that both macrophage types are induced to metabolize arachidonic acid by various particulate and soluble stimuli. Furthermore, we have shown that intravascular macrophages predominantly utilize the lipoxygenase rather than cyclooxygenase pathways to metabolize endogenous arachidonic acid.