Alteration of the erythrocyte ultrastructure and blood viscosity by morphine

The effects of acute morphine administration on intact erythrocytes and on their flow properties were studied by measuring the mean cell volume, cell geometry, and whole blood and plasma viscosities. Morphine caused a small (2-7%) increase in mean cell volume. Changes in cell geometry were found to be time dependent and most pronounced in concave portions of the red cells. Whole body viscosity was found to decrease upon morphine treatment; this may be due in part to a concurrent decrease in plasma viscosity.