Glucose use and pentose cycle activity were determined in freshly isolated rat hepatic endothelial cells 3 hr after an intravenous injection of Escherichia coli lipopolysaccharide (0.1 mg/kg body weight), by use of (1-14C)glucose, [6-14C]glucose and [2-H]glucose. Lipopolysaccharide treatment in vivo increased glucose use fivefold, whereas glucose oxidation in the pentose cycle was elevated from 0.2 to 1.5 nmol/hr/107 cells. In vitro incubation of endothelial cells from saline- and lipopolysaccharide-treated animals in the presence of phorbol 12-myristate 13-acetate (10−6 mol/L) increased pentose cycle activity twofold and eightfold, respectively. Phorbol 12-myristate 13-acetate caused only a 40% to 60% increase in glycolysis in both groups. Addition of t-butyl hydroperoxide (0.5 mmol/L), a substrate for gluathione peroxidase, caused a 24-fold and 16-fold increase in the glucose flux through the pentose cycle in cells from saline- and lipopolysaccharide-treated rats, respectively. Oxidation of glucose through the Krebs cycle was also increased several-fold after t-butyl hydroperoxide administration. Depletion of cellular glutathione by N-ethylmaleimide (0.1 mmol/L) inhibited the phorbol 12-myristate 13-acetate–induced or t-butyl hydroperoxide–induced increase in the pentose cycle activity with no marked effects on glycolysis. Diphenyleneiodonium (0.1 mmol/L), an inhibitor of superoxide and nitric oxide synthesis inhibited the phorbol 12-myristate 13-acetate–induced increased pentose cycle activity with no effects on the t-butyl hydroperoxide–induced response. Endothelial cells from control animals treated with either 12-myristate 13-acetate or t-butyl hydroperoxide in the presence of exogenous glucose 20 mmol/L showed a similar increase in glycolysis but less increase in the pentose cycle activity as found after lipopolysaccharide treatment in the presence of glucose 5 mmol/L. This finding suggests that glucose-6-phosphate dehydrogenase or pathways dependent on pentose cycle intermediates became up-regulated after lipopolysaccharide administration. The lipopolysaccharide-induced elevated glucose use, accompanied by an increased activity of the pentose cycle, may also represent a potentiated mechanism for eliminating hydrogen peroxide derived from intracellular sources or from activated Kupffer cells and sequestered neutrophils in the hepatic sinusoid. (HEPATOLOGY 1993;17:615–620.)