The disaggregation effect of Dextran 40 on red cell aggregation in macromolecular suspensions 1

Red blood cells aggregate to form rouleaux and cause elevation of blood viscosity at low shear rates in the presence of plasma proteins and other macromolecules. Low molecular weight dextran with a molecular weight of 40,000 (Dx 40) has been postulated to cause disaggregation of RBCs in blood. Plasma proteins and dextran with a molecular weight of 63,000 (Dx 70) were used to induce RBC aggregation in the present investigation. Dx 40 was added to the suspensions at concentrations up to 10 g/dl to study the mechanisms of its disaggregation effect. The relative viscosity at a shear rate of 0.05 sec⁻¹ and a hematocrit value of 45 percent (n_r) was used to indicate the degree of RBC aggregation. Suspensions of normal RBCs in Dx 70-saline (in the absence of Dx 40) showed an increase in n_r as Dx 70 concentration was raised to 4 g/dl; further increases in Dx 70 concentration resulted in a progressive decrease in n_r. When Dx 40 was added to RBC suspensions in Dx 70-saline, a significant reduction of n_r was found. The surface potential (determined in a cell microelectrophoresis apparatus) of normal RBCs increased significantly when Dx 40 was added to Dx 70-saline. With the use of neuraminidase-treated RBCs, Dx 40 did not exhibit disaggregation effects on Dx 70-induced RBC aggregation. These results indicate that the disaggregation effect of Dx 40 on Dx 70-induced RBC aggregation is primarily due to the elevation of RBC surface potential by Dx 40. Addition of Dx 40 to plasma, besides causing an elevation of RBC surface potential, also resulted in a significant reduction of fibrinogen concentration. Analysis of the results indicates that the disaggregation effect of Dx 40 on RBCs in plasma is due to a combined effect of an increase in surface potential and the precipitation of fibrinogen by Dx 40.