Renal handling of aluminium

Aluminium (Al) is absorbed from a variety of foodstuffs and medications. Its major route of elimination from the body is in the urine. However, current knowledge concerning its glomerular filtration and, more particularly, its reabsorption/secretion is fragmentary. Most (80-90%) of Al in the plasma is normally bound to protein (mainly transferrin) and is therefore unfilterable; the remainder is bound to low molecular mass compounds, of which citrate appears to be the most important. In vitro determinations using artificial membranes indicate that approximately 10% of Al is filtered at normal plasma concentrations. However, when plasma Al is raised experimentally, its filterability falls, unless the excess Al is complexed with citrate; the aluminium citrate complex appears to be freely filtered. Information on tubular Al reabsorption at normal plasma concentrations is inconsistent. Filtered Al appears to be at least partially reabsorbed, although the reabsorptive mechanisms remain speculative. A consensus is emerging that elevated plasma Al concentrations result in a fall in fractional Al reabsorption, and a recent micropuncture study indicates that under these circumstances the only significant site of Al reabsorption is the loop of Henle.