Changes in the Composition of the Red Blood Corpuscle During Fat Absorption.

The composition of the red blood corpuscle may be altered physiologically by the simple expedient of feeding a fat, such as olive oil. The changes thus produced have been studied by Bloor, 1 Knudson 2 and others and it has been determined that during fat absorption there is an increase in the lecithin content of the blood which runs more or less parallel to the change in total fatty acids, the increase being more marked in the corpuscles than in the plasma. As regards cholesterol, Knudson has shown that the esters of this substance increase in amount during fat absorption, particularly in the corpuscles, where normally little or no cholesterol is present in the ester form.

These changes have been considered of significance chiefly from the standpoint of fat transport and metabolism and the suggestion has been made that the red blood cells absorb the fat from the plasma, transform it into lecithin and that thus the red blood corpuscles play a part in the transportation and metabolism of fat. Our interest in the problem has been in relation to the alterations in permeability of the red blood corpuscle accompanying changes in the composition of its lipid constituents. The frequently cited data of Knudson obtained in his study of fat absorption of dogs are of unquestioned accuracy, but their physiological significance may be made more apparent if represented in terms of molecular equivalents. At any time during absorption, the millimolar increase of cholesterol, present as esters, plus 2 × the millimolar increase of lecithin, obviously represent the increase, in millimols, of the fatty acid present in combination with cholesterol and as phosphatide. The remainder may be supposed to exist almost entirely as neutral fat and soap.