RED-BLOOD-CELL SIZE IS IMPORTANT FOR ADHERENCE OF BLOOD-PLATELETS TO ARTERY SUBENDOTHELIUM

Abstract

The hematocrit is one of the main factors influencing platelet adherence to the vessel wall. Raising the hematocrit causes an increase of platelet accumulation of about an order of magnitude. The role of red cell size was studied. This effect was studied using an annular perfusion chamber, with human umbilical arteries and a steady-flow system. Normal human red blood cells (MCV [mean corpuscular volume] 95 cu .mu. [cubic micron]) increased platelet adherence sevenfold, as the hematocrit increases from 0 to 0.6. Small erythrocytes from goats (MCV 25 cu .mu.) caused no increment in adherence in the same hematocrit range. Rabbit erythrocytes (MCV 70 cu .MU.) caused an intermediate increase in adherence. Red blood cells from newborns (MCV 110-130 cu .mu.) caused a larger increase in platelet adherence than normal red cells at hematocrit 0.4. These results were further confirmed with large red blood cells from 2 patients. Experiments with small red cells (MCV 70 cu .mu.) of patients with Fe deficiency showed that platelet adherence was similar to normal red cells, provided the red cell diameter was normal. Small red blood cells of a patient with sideroblastic anemia caused decreased adherence. Red cell size apparently is of major importance for platelet adherence. Red cell diameter is more important than average volume. For size differences in the human range, the hematocrit remains the dominant parameter.