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Toll-like receptor 4 (TLR4) represents an important mediator of endotoxin-related signal transduction. The aim of our study was to evaluate whether TLR4 inhibition after onset of experimental endotoxemia is able to improve the intestinal microcirculation, which is crucial in the pathogenesis of septic multiple organ failure.
We studied four groups of animals (Lewis rats, n = 10 per group): healthy controls (CON group), endotoxemic animals (15 mg/kg lipopolysaccharide, LPS group), endotoxemic animals treated with TLR4 antagonist (1 mg/kg CRX-526, LPS + CRX group), and CRX-526 treated controls (CRX group). Intravital microscopy of the intestinal microcirculation was performed following 2 hours of observation in all animals. Blood samples were taken for cytokine measurements at the end of the experiments.
Following 2 hours of endotoxemia we observed a significant increase of leukocyte adhesion in the intestinal submocosal venules (for example, V1 venules: CON 20.4 ± 6.5 n/mm2, LPS 237.5 ± 36.2 n/mm2, P < 0.05). Capillary perfusion of the muscular and mucosal layers of the intestinal wall was significantly reduced (for example, longitudinal muscular layer: CON 112.5 ± 5.9 cm/cm2, LPS 71.3 ± 11.0 cm/cm2). TLR4 inhibition reduced leukocyte activation (V1 venules: 104.3 ± 7.8 n/mm2) and improved capillary perfusion (longitudinal muscular layer: 111.0 ± 12.3 cm/cm2) significantly. Cytokine release was not affected.
Administration of the TLR4 antagonist CRX-526 improved intestinal microcirculation in a post-treatment model of experimental endotoxemia. The TLR4 pathway may be a target in clinical Gram-negative sepsis.