The attenuation of hemorrhage-induced liver injury by exogenous nitric oxide, L-arginine, and inhibition of inducible nitric oxide synthase.

We investigated the role of nitric oxide (NO) in its ability to reduce liver injury in an animal model of hemorrhagic shock (HS). Ninety-six Sprague-Dawley rats weighing 250 to 300 g were divided in 6 groups (n = 16 per group) that included treatment at the beginning of resuscitation with normal saline (groups 1, 3) sodium nitroprusside (NP) (0.5 mg/kg) (groups 2, 4) L-arginine (300 mg/kg) (group 5), and L-N6-(1-iminoethyl) lysine (L-NIL, 40 mg/kg) (group 6). The experimental model of HS consisted of the withdrawal of 3 mL blood per 100 g in a 15-min period, tail amputation (75%), and drug administration at 30 min. This was followed by fluid resuscitation (FR) with lactated Ringer's (LR) solution to reach a mean arterial pressure (MAP) of 40 mm Hg, then a hospital phase of 60 min with hemostasis and FR with LR solution to reach a MAP of 70 mm Hg with a 3-day observation phase. NP, L-Arginine, and L-NIL significantly reduced fluid requirements for resuscitation (p =.0001) as well as significantly increased MAP after resuscitation from hemorrhage. We also observed an improved statistically significant difference (p =.001) in tests demonstrating less hepatic injury and histology damage. The mRNA expression of cytokines in the liver (interleukin [IL]-1alpha, IL-beta1, tumor necrosis factor [TNF]beta, IL-3, IL-4, IL-5, IL-6, IL-10, TNFalpha, IL-2, interferon [IFN]gamma) was reduced by NP treatment, L-arginine, and L-NIL. These data suggest that excess NO mediates hemorrhage-induced liver injury and that the suppression of inducible nitric oxide synthase (iNOS)-generated NO bioavailability with the NO donor sodium nitroprusside may reduce the pathophysiologic consequences of severe hemorrhage. This effect could be possibly related to the scavenging of to superoxide radicals (O2-) or the blockade of the deleterious effects of TNF and other inflammatory cytokines. The protective action noted with L-arginine cannot be fully explained within the context of this article, although it could be most likely associated with the supplementation of eNOS-generated NO.