Superoxide Anion Generation in the Liver During the Early Stage of Endotoxemia in Rats

Abstract

Infiltration of polymorphonuclear neutrophils (PMN) in the rat liver 3 hr after an intravenous (IV) injection of a sublethal dose of Escherichia coli lipopolysaccharide (LPS) was observed without any significant alteration in the total number of Kupffer and endothelial cells. Since previous studies have demonstrated that phagocytic cells in the liver were in a state of metabolic activation under similar experimental conditions, we investigated the in vitro generation of superoxide anion (O₂ ^-) by this cell type following the administration of LPS. Kupffer cells from normal rats did not release O₂ ^-, in contrast to those obtained from LPS-treated rats. The generation of O₂ ^- by Kupffer cells from endotoxic rats was elevated from 3.0 ± 1.9 nmol/10⁶ cells/60 min (mean ± SD) in the absence of macrophage (Mφ) activators, to 5.0 ± 2.36, 11.33 ± 5.40, and 4.33 ± 0.90 in the presence of opsonized zymosan, phorbol myristate acetate (PMA), and the calcium ionophore A23187, respectively. Hepatocytes from normal or endotoxic rats did not produce detectable O₂ ^-. Endothelial cells from LPS-treated rats generated < 0.8 nmol/10⁶ cells in the presence of zymosan. PMN that accumulated in the livers of endotoxic rats released O₂ ^- only in the presence of zymosan (8.12 ± 5.40), PMA (15.43 ± 5.84), or A23187 (1.70 ± 0.12). The O₂ ^- generation by blood monocytes and PMN increased significantly after endotoxin administration and in the presence of activators. These results suggest that the hypermetabolic state of phagocytic cells in the liver shortly after LPS treatment may be correlated with the increased generation of O₂ ^-. The latter may subsequently contribute to the induction of hepatic injury in endotoxemia.