The aim of the present study was to investigate the role of poly (ADP-ribose) synthetase in acute local inflammation (carrageenan-induced pleurisy), where oxyradicals, nitric oxide and peroxynitrite are known to play a crucial role in the inflammatory process. DNA single-strand breakage and activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) triggers an energy-consuming, inefficient repair cycle, which contributes to peroxynitrite-induced cellular injury. Here we investigated whether peroxynitrite production and PARS activation are involved in cytotoxicity in macrophages collected from rats subjected to carrageenan-induced pleurisy. Macrophages harvested from the pleural cavity exhibited a significant production of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, and by nitrotyrosine Western blotting at 4 hr after carrageenan injection. Furthermore, carrageenan-induced pleurisy caused a suppression of macrophage mitochondrial respiration, DNA strand breakage, activation of PARS and reduction of NAD+ cellular levels. In vivo treatment with 3-aminobenzamide (10 mg/kg intraperitoneally, 1 hr after carrageenin injection) significantly inhibited the decrease in mitochondrial respiration and the activation of PARS and partially restored the cellular level of NAD+. In a separate group of experiments, in vivo pretreatment with NG-nitro-L-arginine methyl ester, a non-selective inhibitor of nitric oxide (NO) synthesis (10 mg/kg intraperitoneally, 15 min before carrageenan administration), reduced peroxynitrite formation and prevented the appearance of DNA damage, the decrease in mitochondrial respiration and the loss of cellular levels of NAD+. Our study suggests that formation of peroxynitrite and subsequent activation of PARS may alter macrophage function in inflammatory processes and inhibition of NO and PARS may be a novel pharmacological approach to prevent cell injury in inflammation.