The purpose of this study was to examine whether selective iNOS inhibition can restore the hemodynamic changes and reduce the nitrotyrosine levels in the cerebral cortex of rats with streptozotocin-induced diabetes during endotoxin-induced shock. The study was designed to include three sets of experiments: (1) measurement of changes in systemic hemodynamics, (2) measurement of biochemical variables, including iNOS activity and nitrotyrosine formation in the brain, and (3) assessment of mortality rate. Rats were randomly divided into four groups: group 1, control; group 2, LPS: Escherichia coli endotoxin, 10.0 mg/kg (i.v.) bolus; group 3 (i.v.) LPS and L-N6-(1-iminoethyl)-lysine (L-NIL), 4mg/kg (i.p.); and group 4, LPS and NG-nitro-L-arginine methyl ester (L-NAME), 5 mg/kg (i.p.). In nondiabetic rats, administration of L-NIL prevented the hemodynamic and biochemical changes, and increases in plasma nitrite and cerebral nitrotyrosine levels induced by LPS. Administration of L-NAME partially prevented these LPS-induced changes. On the other hand, in diabetic rats, administration of L-NIL only partially prevented the hemodynamic and biochemical changes, and increases in plasma nitrite and cerebral nitrotyrosine levels associated with LPS. Administration of L-NAME, however, had no effects on these LPS-induced changes in diabetic rats. There was a significant difference in nitrotyrosine levels between nondiabetic and diabetic rats in groups 2, 3, and 4 at 2 and 3 h after the treatment (at 3 h; nondiabetic--control, 4.6 +/- 0.4; LPS (i.v.), 8.9 +/- 1.0, LPS (i.v.) + L-NIL, 4.7 +/- 0.5; LPS (i.v.) + L-NAME, 7.1 +/- 0.9; diabetic--control, 5.5 +/- 0.4; LPS (i.v.), 13.6 +/- 1.2; LPS (i.v.) + L-NIL, 9.0 +/- 0.9; LPS (i.v.) + L-NAME, 13.0 +/- 1.0; densitometric units). Insulin therapy resulted in a decrease in iNOS activity (at 3 h: 1.0 +/- 0.5 fmol mg min), nitrotyrosine formation (at 3 h; 5.0 +/- 0.5, densitometric units), and mortality rates (30% at 6 h, 50% at 12 h) in the LPS (i.v.) + L-NIL group of diabetic rats. Selective iNOS inhibition in diabetic rats could not improve hemodynamic instability, chemical changes, iNOS activity, and nitrotyrosine formation during septic shock compared with the improvements observed in nondiabetic rats. Tight glucose control along with administration of L-NIL can result in more effective restoration of the biochemical changes of septicemia in diabetic rats. Thus, hyperglycemia may be one of the mechanisms related to the aggravation of endotoxin-induced shock.