Microhemodynamic and cellular mechanisms of activated protein C action during endotoxemia

Objective: To characterize microcirculatory actions of activated protein C in an endotoxemia rodent model that allows in vivo studies of microvascular inflammation and perfusion dysfunction. Design. Animal study using intravital microscopy. Setting. Animal research facility. Subjects: Male Syrian golden hamsters, 6-8 wks old with a body weight of 60-80 g. Interventions: In skinfold preparations, endotoxemia was induced by intravenous administration of 2 mg/kg endotoxin (lipopolysaccharide, Escherichia coli). Intravital microscopy allowed quantitative analysis of arteriolar and venular leukocyte adhesion and functional capillary density (cm(-1)) that served as a measure of microvascular perfusion failure. Activated protein C (APC group, n = 8, 24 mug/kg intravenously) was substituted continuously during 8 hrs after lipopolysaccharide, whereas endotoxemic buffer-treated animals (control, n = 7) served as controls. Measurements and Main Results. Lipopolysaccharide increased leukocyte adhesion and decreased functional capillary density to 50% of baseline values (p <.01 vs. baseline). Activated protein C treatment inhibited (p <.05) lipopolysaccharide-mediated leukocytic response and attenuated (p <.05) endotoxic perfusion failure in nutritive capillaries. Conclusions: Activated protein C-induced protection from lipopolysaccharide-mediated microcirculatory dysfunction was characterized in vivo for the first time. The impressive modification of leukocyte cross-talk indicates systemic anti-inflammatory activated protein C effects on leukocytes and the endothelium, subsequently improving capillary perfusion. These actions could represent the in vivo mechanism of activated protein C interactions observed in patients with severe sepsis.