Blood α‐tocopherol: Erythrocyte and plasma relationships in vitro and in vivo

When rat plasma labeled with3H‐α‐tocopherol was incubated with tocopherol‐deficient red cells, uptake of radioactivity by cells was rapid with a maximum being reached in 6–8 hr. The equilibrium ratio of red cell‐plasma α‐tocopherol, from 0.3–0.6, was independent of the initial plasma concentration. When labeled red cells were incubated with tocopherol‐deficient plasma, radioactivity in plasma became maximal in 11.5 hr. When both plasma and cells had normal α‐tocopherol concentrations initially, the rate of exchange was similar in either direction with equilibrium of specific activity being attained in 6 hr. After a single oral dose of3H‐α‐tocopherol the activity in both plasma and cells reached a maximum in 8 hr and then fell rapidly during the next four days. The ratio of red cell‐plasma radioactivity at all intervals after 8 hr was 0.5.