Compartmental analysis of magnesium kinetics in Mg-sufficient and Mg-deficient rats

In this study, we determined magnesium kinetic values in normal rats using stable-isotope techniques. Additionally, we calculated the mass of the exch angeable pools of Mg in Mg-deficient rats to determine whether it can be us ed as a marker of Mg status. Rats were fed either a control diet (1,000 mg Mg/kg) or a Mg-deficient diet (60 mg Mg/kg). After 2 weeks on the experimen tal diets, each rat received an intravenous injection of Mg-26. The plasma Mg disappearance curve over the next 7 days was used to measure the mass an d fractional transport rate of 3 rapidly exchanging Mg metabolic pools. In control rats, the mass of pool 1 (1.37 mg) was half that of pool 2 (2.46 mg ), and pool 3 (47.7 mg) accounted for greater than 90% of exchangeable Mg. In Mg-deficient rats, we observed a significant decrease in the size of the 3 exchangeable pools of Mg (0.36, 0.72, and 20.2 mg, respectively) relativ e to the control rats. Furthermore, the fractional transport rate of Mg fro m pool 1 to pool 3 in Mg-deficient rats was 3 times the rate in the control rats, and the rate of irreversible loss from pool 1 was lower in Mg-defici ent rats. In summary, this study allows us to establish Mg kinetic data in Mg-sufficient and Mg-deficient rats. The present experiment supports the co nclusion that the isotopic test identifies animals with severe Mg deficienc y. Copyright (C) 2000 by W.B. Saunders Company.