Early biochemical events in pneumococcal otitis media: Arachidonic acid metabolites in middle ear fluid

The concentrations of four arachidonic acid metabolites, prostaglandin E2, 6-keto-prostaglandin F1α, leukotriene B4, and leukotriene C4, were measured in middle ear fluid of chinchillas 6 to 72 hours after middle ear inoculation of log-phase, heat-killed encapsulated Streptococcus pneumoniae organisms. Compared with saline-inoculated ears, significant increases in the mean concentrations of all four metabolites were observed in the pneumococcus-inoculated ears 24 hours after inoculation, but not after 6, 48, or 72 hours. Since pneumococcus inoculation caused an influx of inflammatory cells as early as 6 hours after inoculation, before the increase in arachidonate metabolites, the initial stimulus for inflammatory cell chemotaxis is probably not metabolic products of arachidonic acid such as leukotriene B4. These metabolites may, however, amplify the subsequent inflammatory response.