Hypermagnesemia does not increase brain intracellular magnesium in newborn swine

Phosphorus-31 magnetic resonance spectroscopy was used in 2-day (n = 4) and 40-day (n = 4) miniswine to determine whether plasma hypermagnesemia alters brain intracellular magnesium concentration and if the plasma-brain intracellular magnesium relationship changes with age. At control, brain intracellular magnesium concentration was similar in the 2-day (0.24 ± 0.04 mM) and 40-day groups (0.21 ± 0.01 mM). Intravenous infusions of magnesium sulfate (MgSO 4, 60 minute) raised plasma magnesium concentration to 4-6 mM in both groups. During and for 3 hours after MgSO 4 infusions, there were no changes in brain intracellular magnesium concentration in either group and no correlation between plasma and brain intracellular magnesium ( r = 0.11 and 0.08 for 2- and 40-day groups, respectively). Brain intracellular magnesium concentration appears to be tightly regulated.