Roles for platelet-activating factor and *NO-derived oxidants causing neutrophil adherence after CO poisoning

Studies were conducted with rats to investigate whether platelet activating factor (PAF) and nitric oxide (*NO)-derived oxidants played roles in the initial adherence of neutrophils to vasculature in the brain after carbon monoxide (CO) poisoning. Before CO poisoning, rats were treated with the competitive PAF receptor antagonist WEB-2170 or with the peroxynitrite scavenger selenomethionine. Both agents caused significantly lower concentrations of myeloperoxidase in the brain after poisoning, indicating fewer sequestered neutrophils. Similarly, both agents reduced the concentration of nitrotyrosine, indicating less oxidative stress due to *NO-derived oxidants. There were no alterations in whole brain homogenate PAF concentration measured by immunoassay and bioassay, nor were there changes in phosphatidylcholine concentration. Immunohistochemical imaging showed PAF to be more heavily localized within perivascular zones after CO poisoning. Neutrophils colocalized with both PAF and nitrotyrosine in brains of rats killed immediately after CO poisoning. We conclude that qualitative changes in brain PAF are responsible for neutrophil adherence immediately after CO poisoning and that activated neutrophils trigger the initial rise in brain nitrotyrosine. Persistent PAF-mediated neutrophil adherence required production of *NO-derived oxidants because when oxidants were scavenged, neutrophil adherence was not maintained.