Improved hepatic glucose production in mice lacking inducible nitric oxide synthase during hyperdynamic septic shock

Introduction

We recently showed in a hyperdynamic mouse model of septic shock that endogenous glucose production is depressed [1]. However, the mechanism for this depression remains unclear. In this context, the role of excess NO release due to activation of the inducible isoform of the NO synthase (iNOS) has been controversially discussed: while Stadler reported a direct relation between excess NO release and the inhibition of gluconeogenesis [2], other authors did not demonstrate any NO effect [3]. We therefore investigated the effects of genetic iNOS deletion on hepatic glucose production in a clinically relevant murine model of normotensive, hyperdynamic, volume-resuscitated septic shock. Wild-type mice served as controls.

Materials and methods

Fifteen hours after induction of sepsis by cecal ligation and puncture, mice were anesthetized, mechanically ventilated and instrumented using a central venous line, ultrasound flow probes on the portal vein (PV) and the superior mesenteric artery (SMA), and combined laser Doppler flowmetry and remission spectroscopy to assess macrocirculatory and microcirculatory blood flows and tissue oxygenation. Normotensive, hyperdynamic hemo-dynamics were achieved by fluid resuscitation with colloids and intravenous noradrenaline (NA) titrated to maintain mean arterial pressure (MAP) >70 mmHg. Stable, nonradioactive isotope-labeled 1,2,3,4,5,6-¹³C6-glucose was infused to calculate the rate of gluco-neogenesis [1] from isotope enrichment in a liver specimen taken at the end of the experiment. Data are the median (range), analysed using Mann-Whitney rank sum tests (intergroup differences).

Results

In iNOS knockout mice, the target MAP was achieved with less than 20% (P < 0.001) of the NA infusion rate required in wild-type mice. SMA and PV flow were significantly lower in iNOS-deficient mice; however, all parameters of gut and liver microcirculatory perfusion and oxygenation were well maintained. Hepatic glucose production was significantly increased in iNOS knockout mice compared with wild-type mice in septic shock (4.3 [3.2–8.4] vs 1.9 [0.4–2.9] mg/g*hour, P < 0.001) despite reduced NA infusion rates.

Conclusion

Since hepatic microvascular perfusion and oxygenation were well maintained in iNOS-deficient mice, our results of improved hepatic glucose production during hyperdynamic, volume-resuscitated septic shock support the concept that an iNOS-mediated inhibition of cellular energy metabolism rather than a deficiency in oxygen supply contributes to hepatic dysfunction in septic shock.