Exchangeable magnesium pool masses reflect the magnesium status of rats

A sensitive and valid marker to assess magnesium (Mg) status in humans is n ot available. The kinetically determined exchangeable pool masses have been used for other minerals, such as zinc and selenium, as markers of whole-bo dy mineral status. To evaluate the validity of this relationship for Mg, we measured the exchangeable pools of Mg in rats over a range of magnesium di etary intakes. Rats weighing similar to 170 g were fed a control diet (500 mg Mg/kg), a marginally Mg-deficient diet (200 mg/kg) or a severely Mg-defi cient diet (60 mg Mg/kg) for 2 wk. Subsequently, rats were administered an intravenous injection of Mg-25,and the plasma Mg-25 disappearance curve was followed for the next 7 d. The following two methods were employed to anal yze the exchangeable pools of Mg: 1) formal compartmental modeling and 2) a simplified determination of the total mass of the rapidly exchangeable Mg pool (EMgP). The mass of the three exchangeable pools (two extracellular po ols and one intracellular pool) determined by compartmental analysis decrea sed in proportion to dietary Mg intake. EMgP, the combined pools of Mg that exchange with the plasma Mg within 48 h, decreased significantly as dietar y Mg was lowered. It was positively correlated with conventional markers of Mg status (total Mg in plasma, erythrocyte and tibia Mg levels). Compartme ntal analysis assesses Mg exchangeable pools more accurately, but determina tion of EMgP is simpler and faster. Our findings demonstrate that the excha ngeable pools of Mg constitute a good marker of Mg status in rats.