Factors affecting the exchange of tocopherol between red blood cells and plasma.

The purpose of this study was to clarify factors that affect the equilibrium distribution of alpha-tocopherol between red blood cells and plasma. Plasma labeled with 14C-alpha-tocopherol was incubated with red cells for 4 to 6 hr and the distribution of the tocopherol determined in the two compartments (red blood cell (RBC: plasma ratio). Use of heparin as anticoagulant gave a higher RBC: plasma ratio than acid citrate dextrose. The RBC:plasma ratio was affected by the hematocrit of the incubation mixture, higher ratios being obtained with lower hematocrits. The ratio was not related to the plasma concentration of alpha-toxopherol, indicating that the red cell was not saturated up to four times normal plasma levels. Of possible clinical significance was the finding that the RBC: plasma ratio was related to the total lipid concentration of plasma. Red cell content of alpha-tocopherol decreased as plasma lipids increased, until at three times normal plasma lipid concentration the red cells had one-third or less of their normal concentration of alpha-tocopherol. The implications of this observation on the relationship between plasma and tissue aplha-tocopherol are discussed.