Differential effects of exogenous and endogenously generated H2O2 on phagocytic activity and glucose release of...

Reactive oxygen species play an essential role in necro-inflammatory processes. Therefore, the aim of the present studies was to investigate the effect of exogenous and endogenously produced H2O2 on the phagocytic capacity and glucose release of perfused cirrhotic rat livers in comparison with that on the controls.

Complete septal cirrhosis was achieved by oral treatment of rats with thioacetamide for 6 months. The phagocytic capacity of the perfused livers was measured by the uptake of colloidal carbon. During the continuous perfusion with colloidal carbon, either H2O2 or benzylamine was added to the perfusion medium for a limited time period. The latter functioned as an endogenous H2O2 donor.

In control rats exogenous and endogenously produced H2O2 caused a transient stimulation of the hepatic colloidal carbon uptake as well as of the glucose release. Inhibition of the catalase by aminotriazol doubled the changes evoked by H2O2, whereas blockade of the Kupffer cells by GdCl3 drastically reduced its stimulatory effect. Cirrhotic livers took up less colloidal carbon and released lower amounts of glucose than the controls when stimulated by exogenous H2O2. The inhibition of the nitric oxide synthetase augmented the H2O2-induced effect in controls as well as in the cirrhotic livers by 250% and 620% (colloidal carbon uptake) and 340% and 760% (glucose release), respectively. The blockade of the eicosanoid production by indomethacin and caffeic acid drastically increased the glucose release and the colloidal carbon uptake in controls and, in absolute terms, to a lesser extent in cirrhotic livers. Endogenous H2O2 produced by the addition of benzylamine stimulated the colloidal carbon uptake and glucose release in livers from both groups. The inhibition of the lipoxygenase increased both parameters, whereas different effects were elicited by the addition of superoxide dismutase in controls and cirrhotic livers.

The maximum uptake of colloidal carbon and glucose release, measured after stimulation by H2O2, was lower in cirrhotic livers than in controls, thus indicating a lowered phagocytic capacity of Kupffer cells and altered glycogenolytic response of the hepatocytes in cirrhotic livers. The use of various effectors provided evidence that superoxide anions, nitric oxide and, possibly, arachidonic acid are involved in the signal transduction between Kupffer cells and hepatocytes when stimulated by exogenous or endogenously produced H2O2. This signalling mechanism seems to be impaired in cirrhotic livers.