ACUTE ENDOTOXIN TOLERANCE DOWN-REGULATES SUPEROXIDE ANION RELEASE BY THE PERFUSED LIVER AND ISOLATED HEPATIC NONPARENCHYMAL CELLS

This work is based on the hypothesis that low-dose lipopolysaccharide (LPS) suppresses the stimulatory and priming effects of a subsequent h igh-dose endotoxin on the formation of toxic oxygen-derived radicals b y the perfused liver and isolated hepatic nonparenchymal cells. Such e ffects may in turn contribute to hyposensitivity to the lethal effect of large doses of endotoxin. Male Sprague-Dawley rats received a nonle thal (''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. Non parenchymal cells were also isolated for the determination of superoxi de anion formation in vitro. There was a low rate (0.14 +/- 0.1 nmol/m in/g liver weight) of superoxide generated by the perfused livers from rats that received the low-dose LPS 1 to 5 days previously. Control l ivers 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 live r 4 hours after treatment of previously untreated control rats with la rge-dose LPS. This was attenuated to 0.7 +/- 0.04 nmol/min/g by an inj ection of low-dose LPS before challenge. This attenuation was time dep endent; it failed to manifest at 12, 24, or 120 hours after low-dose L PS. Isolated endothelial cells, Kupffer cells, and sequestered hepatic neutrophils from rats given a high-dose LPS also generated significan t amounts of superoxide both in the presence or absence of agonists, i .e., phorbol myristate acetate or opsonized zymosan. Pretreatment of r ats with the low dose of LPS 48 hours before the large dose attenuated the spontaneous and primed release of superoxide by isolated nonparen chymal cells. Serum transaminase activities were also reduced in these LPS-tolerant rats. The suppressed oxygen-derived radical formation by the liver and nonparenchymal cells during acute LPS tolerance was ass ociated with down-regulation of tumor necrosis factor (TNF) release in vivo. TNF has been shown to stimulate and prime neutrophils and Kupff er cells for increased respiratory burst. These results suggest that s uppression of free radical formation may contribute to the amelioratio n of hepatic injury during acute endotoxin tolerance.