DEVELOPMENTAL-CHANGES IN TRANSFERRIN AND IRON UPTAKE BY THE BRAIN IN THE RAT

The uptake of transferrin and iron by the brain, liver and femurs was investigated in rats using 125I-59Fe-transferrin (Tf), and 131I-albumin in order to measure the plasma content of the organs. Measurements in rats ranging in age from birth to 70 days revealed that the rate of iron uptake by the brain increased rapidly over the first 15 days of life, peaking at 15 days and thereafter declining. A similar pattern occurred in the uptake of 125I-Tf. These changes were accompanied by rapid growth of the brain up to 15 days and a decrease in the concentration of non-haem iron. The turnover of 59Fe and 125I-Tf in the brain was also determined by measuring radioactivity in the brain of 15-day rats at various times after injection from 15 min to 13 days. The amount of 59Fe in the brain increased over the first 4 h and thereafter remained constant. By contrast, the 125I-Tf values increased rapidly during the first 15 min to reach a relatively constant level which was maintained for at least 6 h after which it declined. The patterns of uptake by the brain were different from those found in the liver and femurs, indicating that the changes in the brain were specific for that organ. It is concluded that Tf and iron uptake by brain capillary endothelial cells are maximal during the period of rapid brain growth, that iron transport into the brain in the 15-day rat is a uni-directional process while the uptake of Tf by the blood-brain barrier involves two components, one associated with rapid recycling to the circulation and the other with Tf catabolism and transport into the brain. The changes in Tf uptake during the growth phase may be due to the effects of cellular proliferation or iron deficiency on Tf receptor expression. © 1990.