NEW ROLE FOR SERUM FERRITIN (SF) IN IRON METABOLISM

Abstract

This study was designed to determine the origin of SF and its turnover in the rat and in man. The concentration of SF was measured by radioimmunoassay. 59Fe in SF during kinetic studies was measured after ultracentrifugal fractionation of plasma on a sucrose gradient, based on the greater molecular weight of ferritin compared with other iron containing components. After injection of heat-treated 59Fe-RBC in rats, peak labelling of SF fraction was at 30 min; other 59Fe in plasma, primarily transferrin-bound, was maximally labelled at 2 h. No labelling of the SF fraction was detected after injection of 59Fe-transferrin in man or in the rat or after 59Fe-hemoglobin-haptoglobin in the rat. Purified rat liver 59Fe-ferritin, injected intravenously in the rat, was removed by the liver at an exponential rate with a half-life of 4 min. The turnover of SF in man was estimated by an unusual approach, based on an 8-fold higher concentration in the newborn compared with the adult. SF concentration was measured in 10 ml increments of blood removed during 1.5 - 2.0 volume exchange transfusions of the newborn for hyperbilirubinemia. The decrease in serum SF during the 1 h exchanges was slow and of small magnitude. The rate of synthesis of SF was computed to correspond to a half-life as short as 5 min. The rapid turnover of iron in SF, compared with transferrin iron, suggests a quantitatively important role for SF in the transport of iron from the RE cell to the liver.