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Nitric oxide plays a crucial role in the maintenance of liver function and integrity. During stress, the inducible heme oxygenase-1 protein and its reaction products, including carbon monoxide, also exert potent hepatoprotective effects. We investigated a potential relationship between endogenous nitric oxide synthesis and the hepatic regulation of heme oxygenase-1. Inhibition of nitric oxide synthesis in vivo by injection of l-NAME led to a dose-dependent induction of heme oxygenase-1 mRNA, protein and activity in the rat liver, whereas did not affect the expression of other heat shock proteins. The effect of l-NAME was demonstrated by hemodynamic changes within the liver circulation as measured by ultrasonic flow probes. Inhibition of nitric oxide synthase led to a decline in hepatic arterial and portal venous blood flow, and subsequently caused liver cell damage. In contrast, the combined administration of l-NAME and the nitric oxide-independent intestinal vasodilator dihydralazine completely restored portal venous flow, abolished the liver cell damage, and prevented the upregulation of heme oxygenase-1, despite inhibition of nitric oxide production. In conclusion, nitric oxide deficiency upregulates hepatic heme oxygenase-1, which is reversible by maintaining hepatic blood flow. This interdependence has important implications for the development of therapeutic strategies aimed at modulating the activity of these hepatoprotective mediator systems.

The involvement of p38 in fundamental physiological processes and the fact that deregulation often leads to disease indicates the potential impact of p38 dependent mechanisms. Here we demonstrate a new pathway that includes the induction of the mitogen activated protein kinase p38 by protein kinase C and results in a specific phosphorylation of c-Jun in T-lymphocytes. P38 directly phosphorylates c-Jun within its transactivation domain at serine 63 and serine 73 and thus posttranscriptionally affects the presence of DNA-bound phosphorylated c-Jun, a prerequisite for activator protein 1 dependent gene transcription. Moreover, DNA-binding activity of c-Fos, FosB, and JunB were also dependent on the p38 protein kinase activity, whereas JunD, Fra-1 and Fra-2 were not affected. Although we show that stress induced mitogen activated protein kinases share c-Jun as a substrate for phosphorylation, p38 mediated effects could not be rescued by the c-Jun N-terminal kinases. This demonstrates that the protein kinase p38 plays a unique and non-redundant role in posttranslational c-Jun regulation. The induction of a p38 dependent c-Jun phosphorylation was comparable in both CD4(+) and CD8(+) T-cells, proposing a ubiquitous pathway that is not linked to T-cell subtype and effector function. In contrast, ATF-2 was predominantly phosphorylated in CD8(+) T-cells. Different cell lines show p38-dependent c-Jun phosphorylation upon phorbol ester induction but there is evidence that the simian virus 40 large T-antigen may interfere with this pathway.

Background/aims: The heme oxygenase (HO) system contributes to the maintenance of hepatic perfusion and integrity. It was the objective of this study to determine the influence of isoflurane (ISO) on hepatic HO-1 induction and its impact on hepatic hemodynamics., Methods: Rats were pretreated with or without ISO for 5h. After hemodynamic measurements by pressure-, laser doppler-, and ultrasound based techniques, the liver was harvested. HO-1 was analyzed by an HO activity assay, Northern- and Western blotting., Results: ISO pretreatment induced hepatic HO-1 mRNA and protein resulting in an increase of HO activity. No effect on hsp-27, hsp-70 and hsp-90 mRNA could be observed. ISO lowered portal resistance. HO inhibition by tin protoporphyrine IX increased portal resistance in ISO pretreated animals up to control levels. This was associated with an increase in portal pressure and a reduction of portal flow. Microvascular flux was also impaired after HO blockade and ISO. However, hepatic arterial and systemic hemodynamics remained unchanged, indicating a specific effect within the portal vascular bed., Conclusions: ISO pretreatment induces hepatic HO-1 mRNA and protein followed by an increase in HO activity, thereby reducing portal resistance. These findings indicate a beneficial effect of ISO on hepatic hemodynamics in vivo.