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THIRST AND VOLUME, ELECTROLYTE HOMEOSTASIS

A compartmental model of magnesium metabolism in healthy men based on two stable isotope tracers

¹Nestle Water Institute, 88804 Vittel; ²Mass Spectrometry Unit, Institut National de la Santé et de la Recherche Médicale, 31024, Toulouse, France; and ³Western Human Nutrition Research Center, United States Department of Agriculture, University of California, Davis, California 95616

Submitted 9 December 2002 ; accepted in final form 22 May 2003

The aim of this study was to build a compartmental model of magnesium (Mg) kinetics by using data collected from six healthy adult men after oral administration of ²⁶Mg and intravenous administration of ²⁵Mg. Blood, urine, and feces were collected for 12 days after administration of the isotopes. Isotopic ratios were determined by inductively coupled plasma-mass spectrometry. Data were analyzed for each subject using SAAMII. We began with a compartmental model previously proposed (Avioli LV and Berman M. J Appl Physiol 21: 1688-1694, 1966) and developed an alternative approach to resolve the discrepancy between model-predicted curves and experimental data. This analysis enables the exploration of 25% of total body Mg that exchanges rapidly from plasma compartment with two extraplasma pools. One of the extraplasma compartments contains 80% of the exchangeable Mg with a transport rate of 48 ± 13 mg/h. The second exchanges 179 ± 88 mg of Mg/h. The model permitted estimation of kinetic parameters as well as fractional Mg absorption and fecal endogenous excretion.

magnesium absorption; magnesium fecal endogenous excretion; inductively coupled plasma-mass spectrometry