Fig. 1. Effect of activation of J774.A1 M on their consumption of O₂ and generation of NO. Activation of M with 10 U ml^-1 IFN and 10 ng ml^-1 LPS progressively inhibited mitochondrial O₂ consumption and concomitantly increased the release of NO into the extracellular fluid (A), and decreased the spare respiratory capacity (B). The different components of cellular O₂ consumption by untreated and SEITU-treated control M did not change throughout the experimental period. Administration of 500 µM SEITU at the time of activation prevented the decrease in cellular (A) and mitochondrial O₂ consumption (not shown) and spare respiratory capacity (B). (C) The non-mitochondrial uptake of O₂ was greatly enhanced after 12 hours of activation; this could be reduced by the administration of 10 µM oxyhaemoglobin or abolished by treatment with SEITU. ^*, Significantly different from values in non-activated cells; , Significantly different from IFN+LPS-treated cells (P<0.05, one way ANOVA, Tukey's post hoc test). Results are mean±s.d., n=5.