title: Problems in the assessment of magnesium depletion in the rat by in vivo 31P NMR.
abstract: Prior in vitro studies, utilizing 31P nuclear magnetic resonance (31P NMR) to measure the chemical shift (sigma) of beta-ATP and lengthening of the phosphocreatine spin-spin (T2) relaxation time, suggested an assessment of their efficacy in measuring magnesium depletion in vivo. Dietary magnesium depletion (Mg2+ decreases) produced markedly lower magnesium in plasma (0.44 vs 1.13 mmol/liter) and bone (130 vs 190 mumol/g) but much smaller changes in muscle (41 vs 45 mumol/g, P less than 0.01), heart (42.5 vs 44.6 mumol/g), and brain (30 vs 32 mumol/g). NMR experiments in anesthetized rats in a Bruker 7-T vertical bore magnet showed that in Mg2+ decreases rats there was a significant change in brain beta-ATP shift (16.15 vs 16.03 ppm, P less than 0.05). These chemical shifts gave a calculated free [Mg2+] of 0.71 mM (control) and 0.48 mM (Mg2+ decreases). In muscle the change in beta-ATP shift was not significant (Mg2+ decreases 15.99 ppm, controls 15.96 ppm), corresponding to a calculated free Mg2+ of 0.83 and 0.95 mM, respectively. Phosphocreatine T2 (Carr-Purcell, spin-echo pulse sequence) was no different with Mg2+ decreases in muscle in vivo (surface coil) (Mg2+ decreases 136, control 142 ms) or in isolated perfused hearts (Helmholtz coil) (control 83, Mg2+ decreases 92 ms). 31P NMR is severely limited in its ability to detect dietary magnesium depletion in vivo. Measurement of beta-ATP shift in brain may allow studies of the effects of interaction in group studies but does not allow prediction of an individual magnesium status.
authors.affiliation: Renal Unit, Repatriation General Hospital (Heidelberg), Melbourne, Australia.
authors.forename: W R
authors.initials: WR
authors.lastname: Adam
authors.forename: D J
authors.initials: DJ
authors.lastname: Craik
authors.forename: J G
authors.initials: JG
authors.lastname: Hall
authors.forename: M M
authors.initials: MM
authors.lastname: Kneen
authors.forename: R M
authors.initials: RM
authors.lastname: Wellard
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008275:Magnesium Deficiency / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D008274:Magnesium