A compartmental analysis of the splenic circulation in rat.

Isolated, acellular washout experiments of 125I-labeled bovine serum albumin (BSA) from control, anemic, and polycythemic rat spleens were used to develop a model of the splenic plasma circulation. The results indicated that the plasma circulation can be described adequately by two compartments. As in red blood cell (RBC) washouts [Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H272-H277, 1980] the fast compartment represents intrasplenic vessels that bypass the red pulp, whereas the intermediate/slow compartment represents plasma flow through the red pulp (filter). The combined plasma and RBC parameters suggest the rat spleen is not an RBC reservoir and that splenic RBC filtration capacity decreases during polycythemia and anemia. The ratio of fast compartment to systemic hematocrit indicates hemodilution occurs, supporting the concept of plasma skimming. A small plasma holdup occurs in the red pulp of anemic and polycythemic spleens probably due to RBC congestion. This congestion, in turn, might be due to reticulocyte sequestration and/or erythropoiesis in anemic spleens and RBC sequestration and/or destruction in polycythemic spleens. There is plasma redistribution in polycythemic spleens possibly to meet the increased metabolic demand.