Time course of various inflammatory mediators during recurrent endotoxemia

Abstract

The time course of thromboxane B 2 (TxB 2), 6-keto-PGF 1α (stable metabolite of prostacyclin), tumor necrosis factor-α (TNF α), platelet activating factor (PAF), and interleukin-6 (IL-6) formation after three lipopolysaccharide (LPS) infusions was studied in pigs over an 18-hr, period. The Escherichia coli endotoxin W0111:B4 was injected i.v. into 10 of the test group pigs at a dose of 0.5μg/kg over 30 min at 0, 5 and 10 hr of the experiment. Three pigs injected with physiological saline served as controls. At defined time points before and after each LPS administration venous blood was withdrawn (0, 15, 30, 45, 60, 120, 180 min) and plasma levels of TxB 2, 6-keto-PGF 1α, PAF, TNF α and IL-6 were determined. Pulmonary artery pressure (PAP) and cardiac output (CO) were measured every 15 min. TxB 2 and PAF peaked significantly between 30 and 45 min, TNF α and 6-keto-PGF 1α between 30 and 60 min, and IL-6 between 120 and 180 min after each LPS injection. The mediators PAF, TNF α and TxB 2 showed a decreasing three-peak profile whereas 6-keto-PGF 1α exhibited an increasing one. IL-6 plasma concentrations increased after each LPS injection. The peak after the third LPS administration, however, was surprisingly low compared to the previous two. The first LPS infusion in our test group led to a significant, sustained rise in mean PAP. After recurrent LPS injections the peak in PAP was not as marked as after the first infusion, indicating the development of a tolerance towards LPS. Initially, CO showed hypodynamic values, whereas the end stage of the experiment was characterized by hyperdynamic CO levels. In conclusion, we believe this porcine model of septic shock to be one of the first large animal models to describe in detail the time-course of various important inflammatory mediators.