Renal handling of magnesium

Abstract

The mechanisms of tubular transport of magnesium (Mg) are still not fully understood. It was presumed by recent in vivo studies that a tubular transport maximum for Mg (TmMg) possibly exists. In addition, it is not clear whether Mg homeostasis is achieved by intrarenal mechanisms or if extrarenal factors are essential in this connection. In order to clarify the conflicting in vivo data, isolated rat kidneys were perfused with a medium containing increasing concentrations of Mg (0.25- to 2-fold of the normal Mg concentration). When Mg in the perfusate was raised linearly, the corresponding urine concentrations showed the typical behavior for a substance with a Tm. In the subnormal level, the urine concentrations run in parallel to the concentrations in perfusate; above this level, urine concentrations increased disproportionally. Other renal functional parameters such as the perfusion flow, glomerular filtration, oxygen consumption or albumin excretion remained unchanged after the addition of Mg to the perfusate. These data suggest that there is a TmMg. The renal Mg threshold concentration seems to be near the normal Mg plasma concentration.