Acute endotoxin tolerance downregulates superoxide anion release by the perfused liver and isolated hepatic nonparenchymal cells

Abstract

This work is based on the hypothesis that low-dose lipopolysaccharide (LPS) suppresses the stimulatory and priming effects of a subsequent high-dose endotoxin on the formation of toxic oxygen-derived radicals by the perfused liver and isolated hepatic nonparenchymal cells. Such effects may in turn contribute to hyposensitivity to the lethal effect of large doses of endotoxin. Male Sprague-Dawley rats received a nonlethal ("low-dose") intravenous injection of Escherichia coli LPS (0.5 mg/kg body weight) 12 to 120 hours before they were challenged by a "large dose" of endotoxin (10 mg/kg). Three hours after LPS challenge, the livers were perfused, and superoxide release was determined. Nonparenchymal cells were also isolated for the determination of superoxide anion formation in vitro. There was a low rate (0.14 +/- 0.1 nmol/min/g liver weight) of superoxide generated by the perfused livers from rats that received the low-dose LPS 1 to 5 days previously. Control livers generated less than 0.08 nmol superoxide. A high rate (1.3 +/- 0.1 nmol/min/g) of superoxide release was measured in the perfused liver 4 hours after treatment of previously untreated control rats with large-dose LPS. This was attenuated to 0.7 +/- 0.04 nmol/min/g by an injection of low-dose LPS before challenge. This attenuation was time dependent; it failed to manifest at 12, 24, or 120 hours after low-dose LPS. Isolated endothelial cells, Kupffer cells, and sequestered hepatic neutrophils from rats given a high-dose LPS also generated significant amounts of superoxide both in the presence or absence of agonists, i.e., phorbol myristate acetate or opsonized zymosan.(ABSTRACT TRUNCATED AT 250 WORDS)