Hepatic Neutrophil Influx: Eicosanoid and Superoxide Formation in Endotoxemia

Abstract

We examined early changes, at 0.5, 1.5, and 3 hr of infusion of a nonlethal dose of Escherichia coli endotoxin (ET) in neutrophil (PMN) sequestration in the liver and accompanying alterations in [1-14C]arachidonic acid metabolism and superoxide anion release by Kupffer and endothelial cells and PMNs. One hundred fifty micrograms ET (268 μg/kg) was infused over 3 hr. Shorter infusions delivered proportionally less ET. By 30 min of ET infusion the number of PMNs in the 45 ml/min fraction was 2.41 × 107, eightfold higher than that in the NaCl-infused rats, representing 35.90 ± 3.49% (n = 7) of the total cell yield vs 8.20 ± 0.20% (n = 4) in NaCl controls. By 90 and 180 min of ET infusion the number of PMNs and their share of the total cell yield increased significantly further. Cells were separated by elutriation, followed by application of a Ficoll-Hypaque gradient, when appropriate. Kupffer cells and PMNs were recovered in the 45 ml/min fraction, endothelial cells in the 23 ml/min fraction. At 30 min of ET infusion the profile of arachidonic acid metabolites released from [1-14C]arachidonic acid-prelabeled nonparenchymal cells upon A23187 stimulation was not different from that of cells of NaCl-infused rats. Infusion of ET for 90 min accentuated PMN infiltration, and resulted in significant modulation of the eicosanoid profile, consisting of a major shift in PGD2/PGE2 to PGE2, and LTB4 and 12-HETE accounting for 34% of the total eicosanoids, compared to 12.9% in time-matched NaCL controls. At 90 min of ET infusion, the mixture of Kupffer cells and PMNs manifested priming for superoxide release upon in vitro stimulation by phorbol myristate acetate and opsonized zymosan. The different time courses of PMN influx and alterations of arachidonic acid metabolism and respiratory burst activity suggest that the mere influx of neutrophils is not sufficient and adequate time for intercellular communication is necessary for the expression of ET-induced changes in paracrine or autocrine regulation of arachidonate metabolism and proximal host defense mechanisms.