The flow properties of individual erythrocytes have been studied in glass micropipets 4 μ internal diameter. The pressure gradient required to establish a standard oscillatory movement over a 130-μ path in a three-second time period was measured in paired studies comparing diabetic and control erythrocytes suspended in Ringer solution. The pressure requirement was regularly elevated for the diabetic erythrocytes, averaging 50 per cent greater than the controls. Studies of erythrocytes comparing alloxan-diabetic rats with control rats demonstrated a similar elevation in required pressure. Red cells from subjects with hereditary spherocytosis offered less flow resistance than diabetic cells, and red cells from rheumatoid arthritics required no pressure increment. When erythrocytes are ejected from a 4-μ micropipet they return quickly to a discoid shape using stored elastic energy. Slow motion photography revealed that diabetic erythrocytes restore their shape less rapidly than nondiabetic erythrocytes, indicating that their reduced deformability is due to an elevation of either intraerythrocyte or membrane viscosity rather than to increased resistance to bending. Diabetes is regularly associated with an increased intracellular hemoglobin Alc; it is possible that hemoglobin Ale could raise intraerythrocyte viscosity. The observed disturbance in flow properties of individual erythrocytes is subtle. It would affect the flow of blood, particularly through active muscle, and modify the pressure exerted by individual erythrocytes on the muscle capillary wall.

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