Studies of the slow bidirectional transport of iron and transferrin across the blood-brain barrier.

Although iron is involved in brain function, very little is known about the regulation of its concentrations in the central nervous system. We quantitatively measured the entry and exit rates of iron, transferrin (its major transport protein), and albumin in mice. The blood to brain transport of iron greater than transferrin greater than albumin and the brain to blood transport of transferrin greater than albumin greater than iron. The results suggest that iron and transferrin have slow, bidirectional, probably saturable, and to some degree independent transport systems, although iron introduced directly into the brain is not readily available for brain to blood transport.