Endotoxin-induced procoagulant activity, eicosanoid synthesis, and tumor necrosis factor production by rat peritoneal macrophages: effect of endotoxin tolerance and glucan.

Macrophages release pro-inflammatory substances that may augment intravascular coagulopathy associated with endotoxemia. In the present study, the effect of Salmonella enteritidis endotoxin on expression of procoagulant activity (PCA), eicosanoid metabolism, and production of tumor necrosis factor (TNF) by rat peritoneal macrophages was determined. Endotoxin induced significant dose-dependent increases in the concentrations of immunoreactive (i) thromboxane B2 (TxB2), 6-ketoprostaglandin F1 alpha (i6-keto-PGF1 alpha), and TNF in culture media. Calcium ionophore (A23187; 0.5 microM) induced an approximate two-fold greater increase (P less than 0.05) in iTxB2 and i6-keto-PGF1 alpha than that stimulated by the maximal endotoxin dose. Endotoxin (0.5, 5, and 50 micrograms/ml) induced similar increases in PCA in macrophage lysates which paralleled the production of iTxB2 and i6-keto-PGF1 alpha. In contrast to its marked effect on eicosanoid metabolism, A23187 elicited little increase in PCA. After the responses of peritoneal macrophages from normal animals were characterized, we hypothesized that procedures which alter the in vivo response of rats to endotoxin would similarly alter the in vitro responses of their peritoneal macrophages. In subsequent studies, the effect of altered endotoxin sensitivity on expression of PCA, eicosanoid synthesis, and TNF activity were assessed. Endotoxin tolerance, induced by repeated injection of sublethal doses of endotoxin in vivo, rendered rat peritoneal macrophages refractory to in vitro endotoxin-induced production of iTxB2, i6-keto-PGF1 alpha, PCA, and TNF activity. In contrast, pretreatment of rats with the macrophage stimulant glucan, which enhances endotoxin lethality, augmented the in vitro production of iTxB2, PCA, and TNF by endotoxin-stimulated peritoneal macrophages. These studies demonstrate that endotoxin-induced macrophage arachidonic acid metabolism is associated with expression of PCA and secretion of TNF. Additionally, macrophage synthesis of these pathogenic mediators is reduced under conditions associated with endotoxin resistance (endotoxin tolerance) and is augmented during endotoxin hypersensitivity (glucan stimulation).