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

Abstract

Sabatier, Magalie, Fré dé ric Pont, Maurice J. Arnaud, and Judith R. Turnlund. A compartmental model of magnesium metabolism in healthy men based on two stable isotope tracers. Am J Physiol Regul Integr Comp Physiol 285: R656-R663, 2003. First published May 29, 2003 10.1152/ ajpregu.00749.2002The 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 26 Mg and intravenous administration of 25 Mg. 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) 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 Ϯ 13 mg/h. The second exchanges 179 Ϯ 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 MAGNESIUM (Mg) is an essential mineral for humans, with a recommended dietary allowance (RDA) of 420 mg/day for adult men (17a). Its physiological role is mainly related to enzyme activity (27), and Mg deficiency has been associated with several pathologies. Despite its importance, minimal information is available regarding the distribution and turnover of exchangeable Mg in humans. The lack of studies of Mg metabolism is due primarily to limitations of the tracers that can be used. The Mg radioisotope has a short half-life (21.8 h), and the precise measurement of the enrichment of relatively abundant stable isotopes presented a challenge until the 1990s for nutrition research. This is accentuated by the fact that few tissues are available for analysis in humans in contrast to animals. These limitations can be overcome in part with compartmental analysis of Mg tracer kinetics, which can be used to obtain quantitative or predictive information about the dynamics of a system. This mathematical description of mineral distribution provides valuable insight into the metabolism of many nutrients in humans (41). Compartmental models have been developed for several essential minerals on the basis of stable isotope studies in humans, including calcium (37, 42, 43), zinc (13, 21, 31, 38 and 39), copper (6, 30), and molybdenum (16,33,34). In addition, parameters deduced from the model can be used as markers of trace element nutritional status. It has been demonstrated for selenium (8,19) and Zn (17) that, depending on the ingested amount of a mineral, pool size could vary and ...

Magnesium Level Changes and its Possible Effects on the Outcome of Patients Admitted to Intensive Care Unit

“…In the current study, there was no relationship between the level of Mg in serum, and age and gender, which was similar to the studies conducted by Sabatier et al (17).…”

“…In the study by Sabatier et al, there was a significant relationship between the level of Mg in serum and renal disease (P value = 0.025); however, in the current study the difference was insignificant (P value = 0.75) (16,17). In the current study, there was no significant relationship between the level of Mg in serum and other cations such as Na, K, and Ca, which was similar to the results of previous studies (16,28,30).…”

Magnesium

“…Magnesium is taken up by passive and active mechanisms which seem not to be regulated. A fractional magnesium absorption of 0.44 was detected with stable isotopes (Sabatier et al 2002). The usual diet provides between 2 and 7.5 mg magnesium per kg body weight.…”

“…The plasma magnesium concentration is in equilibrium with magnesium adsorbed to the surface of bone; hence, bone magnesium represents a buffer for the plasma magnesium concentration (Elin 1994). In a kinetic model of magnesium metabolism in healthy men based on investigations with the stable isotopes 25 Mg and 26 Mg, it has been shown that 24% of the human total magnesium exchanges rapidly; of this amount, 79% turns over in 115 h and the remainder in < 9 h (Sabatier et al 2002).…”

Scientific Opinion on Dietary Reference Values for magnesium

“…The endogenous routes of elimination of absorbed magnesium through the digestive tract are bile, pancreatic and intestinal juices, and intestinal cells; part of these endogenous losses can be reabsorbed (Swaminathan, 2003). Using stable isotopes, endogenous faecal excretion has been determined to be 49 ± 11 mg/day in six healthy men aged 26-41 years (Sabatier et al, 2003b), around 15 mg/day (0.1-0.9 mg/kg body weight per day) in 9-to 14-year-old boys and girls and from 4.7 to 21.7 mg/day in five girls aged 12-14 years, without influence of calcium intake (Sojka et al, 1997).…”