Meconium enhances platelet-activating factor and tumor necrosis factor production by rat alveolar macrophages

Meconium aspiration syndrome (MAS) frequently results in inactivation of surfactant, persistent pulmonary hypertension (PPHN) and respiratory failure among newborn infants. Inflammation and inflammatory mediators play an important role in MAS. Since alveolar macrophages are thought to be very important cells in the pathogenesis of various inflammatory diseases, we evaluated whether meconium could stimulate rat alveolar macrophages to generate platelet-activating factor (PAF) and tumor necrosis factor (TNF)-alpha in vitro. We also examined the response to A23187 (calcium ionophore), 1-0-Hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (synthetic PAF) and dexamethasone on meconium-induced release of PAF and TNF-alpha. PAF and TNF-alpha concentrations from supernatant fluid were measured after high-performance liquid chromatography purification by specific radioimmunoassay, and TNF-alpha concentrations were determined by using an enzyme-linked immunosorbent assay. Our results showed that alveolar macrophages exposed to meconium could enhance PAF and TNF-alpha production in a dose (0.1, 1, 5 and 10%, P<0.01)-dependent way. In the presence of A23187, the capability of meconium to stimulate PAF production was further enhanced in the supernatant fluids. Furthermore, treatment with synthetic PAF significantly increased the generation of TNF-alpha in response to meconium. On the other hand, dexamethasone effectively inhibited both PAF and TNF-alpha production stimulated by 5% meconium (P<0.01, P<0.01; respectively). We suggest that alveolar macrophages and PAF, TNF-alpha play an important role in the pathogenesis of lung injury and severe complications in MAS. Furthermore, the protective effect of glucocorticoids in MAS could be due, at least in part, to a suppression of PAF and TNF-alpha generation.