ObjectiveThe purpose of this study was to determine the role of nitric oxide and poly(ADP-ribose) synthase on impaired mitochondrial function in septic shock.DesignHuman umbilical vein endothelial cells were incubated with serum from ten healthy controls, 20 patients with septic shock, and seven critically ill patients who were not septic. The experiment was repeated after pretreatment with 3-aminobenzamide, a poly(ADP-ribose) synthase inhibitor, orNG-methyl-l-arginine, a nonspecific nitric oxide synthase inhibitor.MeasurementsMitochondrial respiration was measured using a modified MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) assay.SettingResearch laboratory.Main ResultEndothelial cell mitochondrial respiration was significantly depressed by septic serum and averaged 61% ± 6% of control values (p< .05). Incubation with septic serum as compared with control serum also significantly decreased cellular adenosine triphosphate levels (6.7 ± 1.2 nM vs. 13.5 ± 1.9 nM,p< .01). The level of mitochondrial respiration in endothelial cells exposed to septic serum did not correlate with arterial lactate concentration but was correlated with both cardiac output (rs= .52,p< .05) and mixed venous oxygen saturation (rs= .61,p< .05). Pretreatment withNG-methyl-l-arginine significantly increased mitochondrial respiration in endothelial cells treated with septic serum from 63% ± 6% of normal to 88% ± 6% (p< .05) of normal values. Similarly, pretreatment with 3-aminobenzamide increased mitochondrial respiration in endothelial cells treated with septic serum from 64% ± 6% to 100% ± 4% (p< .01) of normal values. Endothelial cells incubated with serum from nonseptic critically ill patients did not demonstrate a significant decrease in mitochondrial respiration.ConclusionIn vitromitochondrial respiration was significantly depressed by septic serum. The addition ofNG-methyl-l-arginine, a nitric oxide synthase inhibitor, and 3-aminobenzamide, a blocker of the poly(ADP-ribose) synthase pathway, significantly attenuated this suppression. These data suggest that nitric oxide and poly(ADP-ribose) synthase activation may play an important role in the inhibition of mitochondrial respiration in septic shock.