Laboratories, Beckenham BR3 3BS. It is clearly established that Gram negative bacterial infections or treatment of animals with bacterial endotoxin results in.
Biochemical SocietVTransactions ( 1 993) 21
Does nitric oxide mediate the inhibitory effects of bacterial endotoxin on hepatic gluconeogenesis? R.A. HORTON, R.G. KNOWLESI AND M.A. TITHERADGE School of Biological Sciences, University of Sussex, Falmer, Brighton BNl 9QG and *Biochemical Sciences, Wellcome Research Laboratories, Beckenham BR3 3BS. It is clearly established that Gram negative bacterial infections or treatment of animals with bacterial endotoxin results in an inhibition of hepatic glucose synthesis in both perfused livers and isolated hepatocytes [I-51. We have demonstrated that the decreased rate of gluconeogenesis results &om an inhibition of substrate flux through phosphoenolpyruvate carboxykinase, with a secondary increase in 6-phosphofhcto-l-kinase activity as a result of an increase in the concentration of fructose 2,6-bisphosphate [3,5]. Recent studies into the mechanisms of hepatocellular dyshnction during sepsis suggest that these responses involve the release of cytokines from the Kupffer cells which interact with the hepatocytes to induce nitric oxide (NO) synthase with concomittant NO production [6 and references therein]. The aim of this study was to investigate whether NO inhibits glucose synthesis in isolated hepatocytes by the use of the artificial NO-donor, S-nitroso-Nacetylpenicillamine (SNAP) and whether the effects are comparable to those of bacterial endotoxin on hepatic carbohydrate metabolism. Fig. 1 shows that addition of SNAP to hepatocytes produced a time and dose-dependent inhibition of glucose synthesis from 10 &-lactate plus 1 mM-pyruvate. Addition of the parent compound, N-acetylpenicillamine (NAP),had no effect on glucose output indicating that the inhibition was due to the formation of NO. To ensure that the effect was not due to metabolites of NO e.g. nitrite and nitrate, hepatocytes were incubated in the presence of 600 pMnitrite or nitrate, however neither compound had any significant effect (data not shown). To examine the possibility that the effect of endotoxintreatment of the rat might be due to the production of NO, the effect of the lipopolysaccharide on gluconeogenesis from a number of substrates feeding into the pathway at different sites was compared with that of SNAP (Table 1). Endotoxin-treatment resulted in an inhibition of glucose synthesis from substrates feeding into the pathway prior to phosphoenol-pyruvate, confirming the suggestion that the major effect of endotoxin-treatment resides at the level of phosphoenolpyruvate carboxy-kinase[3.5]. However the endotoxin also diminished glucose synthesis from both dihydroxyacetone and glycerol, while that from fructose remained unchanged. The latter is consistent with the documented increased cycling at the 6phosphofiucto- 1-kinasdfiuctose- 1,6-bisphosphatase reaction 111 endotoxin-treated animals [2-41.
Table 1. Effect of endotoxin treatment of the rat and SNAP on ucone enesi in isolated he gepatoGes wire incubated of 10 mM substrate.or 10 mM and 1 mM for lactate plus pyruvate. The control cells were incubated in the absence or presence of 600 pM-SNAP. Glucose output was measured between 20-40 mins and are expressed as nmol /20 min per mg wet wt ofcells. * p
