Influence of dietary protein on the properties of the red cell membrane in intact and splenectomized rats.

The possibility that there is some common factor in protein deprivation and splenectomy affecting the properties of red cells was examined by measuring the lipid contents of the plasma and red cells, the surgace area and spherical index of red cells, and the lecithin cholesterol acyltransferase (LCAT) activity of the plasma in intact and splenectomized rats on diets with various levels of protein. Results showed that splenectomy markedly reduced the osmotic fragility and increased the lipid content and surface area of the red cells of all dietary groups, and that decrease in the protein content of the diet gradually reduced the osmotic fragility and increased the lipid content of the red cells. A significant linear correlation was observed between osmotic fragility and the lipid content of red cells. LCAT did not influence the cholesterol level in red cell membranes because its activity in the plasma was not affected by either splenectomy or the protein content of the diet. A protein-free diet induced normaocytic anemia, but increased the lipid content and reduced the osmotic fragility of red cells. Therefore, the effect of cholesterol in increasing the surface area of red cells was not proportional in the red cells of rats on a protein-free diet. The present studies suggest that the mechanism of accumulation of cholesterol in red cells is different in protein deprivation and splenectomy. That is, in protein deprivation, increase in red cell cholesterol may result from decreased esterification of cholesterol in the plasma because of the low concentration of the substrate of LCAT, high density lipoprotein; and in splenectomized rats, the cholesterol level of the cells may not be reduced because the red cells are not exposed to the red pulp of the spleen where the pH is very low. These possibilities are supported by the finding that the osmotic fragility of the red cells decreased most and the lipid content of the cells increased most in splenectomized rats on a protein-free diet.