Acute endotoxic shock is accompanied by an increase sion, vascular injury, disseminated intravascular coagin the production of nitric oxide (NO) by several differulation, and damage to numerous organs. 1 These bioent hepatic cell types. Platelet-activating factor (PAF) is logical responses are thought to be mediated in part a potent proinflammatory mediator with many pathoby the release of proinflammatory substances such as physiological actions and, in fact, elevated plasma and cytokines, lipid mediators, and reactive oxygen and nitissue levels of PAF are observed in animal models of trogen intermediates from granulocytes and macroendotoxic shock. The current study demonstrates that phages after exposure to LPS. [2] Platelet-activating fac-PAF induced nitrite formation, the end product of nitric tor (PAF) is a potent lipid autocoid that exhibits diverse oxide synthesis, by Kupffer cells in a dose-and timepathophysiological activities in various tissues and dependent manner. Moreover, PAF was seen to initiate cells. 5,6 Increased levels of PAF have been detected in NO synthase gene expression and protein synthesis. PAF augmented lipopolysaccharide (LPS)-induced expresthe plasma and tissues of animals subjected to endosion of inducible nitric oxide synthase messenger RNA toxic shock. 7 Moreover, intravenous administration of (mRNA), protein, nitrite and cyclic guanosine mono-PAF mimics several features of endotoxic shock, includphosphate (cGMP) levels in Kupffer cells. Treatment of ing hypotension, peripheral vasodilatation, and cardiac Kupffer cells with actinomycin D or cycloheximide infailure. 9 In addition, PAF stimulation of a variety of hibited PAF-and LPS-stimulated nitrite and nitric oxide cells, including macrophages, endothelial cells, and imsynthase protein formation confirming that de novo synmune cells, results in the release of several other inthesis of the enzyme occurred. In Kupffer cells, the presflammatory mediators. Taken together, these findings ence of an arginine analog, N G -methyl-L-arginine, attenuated nitrite formation induced by PAF and LPS alone indicate that LPS and PAF play critical roles in elevator in combination. L-arginine is the principal substrate ing the inflammatory response in the mammalian body, for nitric oxide synthase. PAF and LPS individually and resulting in tissue damage during endotoxic shock. in combination induced a time-dependent uptake of L-Nitric oxide (NO) is a short-lived free radical that [ 3 H]-arginine into the Kupffer cell, and this response was plays an important regulatory role in several biological sensitive to cycloheximide. The current study indicates processes. 10 The formation of NO from L-arginine and that exogenous PAF contributes to the induction of nimolecular oxygen is catalyzed by the enzyme nitric oxtric oxide synthase by LPS in cultured rat Kupffer cells. ide synthase (NOS). At least three different NOS iso-(HEPATOLOGY 1996;23:1622-1630.)
forms have been identified. 12 The neuronal and endothelial isoforms are expressed constitutively in An array of pathophysiological responses accompany neuronal and endothelial cells, respectively. In these exposure to lipopolysaccharide (LPS), the main compocell types after receptor or physical stimulation, NO nent of bacterial endotoxin, in vivo. The induction of synthesis by the constitutive NOS is regulated mainly endotoxic shock by LPS is characterized by hypotenby calcium influx in a rapid and transient manner. NO produced in this fashion stimulates various intracellular reactions, resulting in several physiological re-Abbreviations: LPS, lipopolysaccharide; PAF, platelet-activating factor; sponses. 11 In contrast, the third NOS isoform, inducible NO, nitric oxide; NOS, nitric oxide synthase; iNOS, inducible nitric oxide syn-NOS (iNOS), is expressed after induction by LPS or thase; cGMP, cyclic guanosine monophosphate; SDS-PAGE, sodium dodecyl various cytokines. 11 iNOS was identified initially in sulfate polyacrylamide gel electrophoresis; mRNA, messenger RNA; TNF, tuperitoneal macrophages and subsequently has been mor necrosis factor.