Fluid extravasation from spleen reduces blood volume in endotoxemia

We recently demonstrated that fluid is filtered out of the splenic circulation and into the lymphatic system. The current experiments were designed to investigate the importance of this route of fluid extravasation in endotoxemia. Lipopolysaccharide (LPS) was infused into conscious intact and splenectomized rats (150 microg x kg(-1). h(-1) i.v. for 18 h). In the intact rats, mean arterial pressure (MAP) fell from 101+/-2.4 to 88+/-3.9 mm Hg (n = 7) and then stabilized at about 90 mm Hg. Hematocrit rose from 41+/-0.9 to 45+/-0.4% at 40 min, at which time plasma volume had fallen from 4.7+/-0.12 to 4.0+/-0.05 ml/100 g body wt. In the splenectomized rats MAP did not fall and hematocrit did not rise. There also was no change in plasma volume, i.e., splenectomy prevented the hypotension and hemoconcentration customarily induced by LPS. In a second series of experiments, splenic arterial and venous blood flows were simultaneously measured in anesthetized rats infused with LPS (150 microg x kg(-1) x h(-1)). LPS increased splenic fluid efflux. We conclude that during endotoxemia the initial fall in circulating blood volume may be attributed to fluid extravasation from the splenic vasculature.