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The hepatic failure associated with severe sepsis is characterized by specific, progressive, and often irreversible defects in hepatocellular metabolism (1). Although the etiologic microbe can often be identified, the direct causes and mechanisms of the hepatocellular dysfunction are poorly understood. We have hypothesized that Kupffer cells (KC), which interact with ambient septic stimuli, respond by providing signals to adjacent hepatocytes (HC) in sepsis . Furthermore, we have provided evidence (2, 3) that KC activated by LPS from Gram-negative bacteria can induce profound changes in the function of neighboring HC in coculture. In our model, coculture of either KC (2) or peritoneal macrophages (M The metabolism of L-arginine by activated M
)(3) with HC normally promotes HC protein synthesis ([(3)H]leucine incorporation). The addition of LPS or killed Escherichia colt' to such cocultures induces a profound decrease in HC protein synthesis, as well as qualitative changes ([(35)S]methionine, SDS-gel electrophoresis) in protein synthesis without inducing HC death (2, 3) . In this report we show that the inhibition in protein synthesis is mediated via an L-arginine-dependent mechanism. to substances with cytostatic and even lethal effects on target cells is a relatively recent discovery. After the description by Stuehr and Marletta (4, 5) that LPS- triggered M produced nitrite/nitrate (NO(2)(-)/NO(3)(-)), Hibbs et al. (6, 7) and Iyengar et al. (8) demonstrated that L-arginine was the substrate for the formation of both these nitrogen end products and citrulline. A role for the arginine-dependent mechanism in M tumor cytotoxicity (6, 7) and microbiostatic activity (9) has been suggested. However, the in vivo functions of this novel M mechanism have not yet been defined, but it is possible that there are both physiologic as well as pathologic roles. Our in vitro results raise the possibility that some metabolic responses to microbial invasion maybe partially mediated by the L-arginine-dependent mechanism. What other metabolic responses are affected and the possible pathologic consequences remain to be studied.
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