Cellular-free magnesium depletion in brain and muscle of normal and preeclamptic pregnancy: A nuclear magnetic resonance spectroscopic study

Preeclampsia is a pregnancy disorder of unknown origin, characterized by vasospasm, elevated blood pressure, and increased neuromuscular irritability, features common to syndromes of magnesium deficiency. Evidence of serum and ionized magnesium metabolism disturbances have been observed in women with preeclampsia. This and the therapeutic utility of magnesium in preeclampsia led us to investigate the extent to which an endogenous tissue magnesium deficiency might be present in and contribute to its pathophysiology. We used 31P nuclear magnetic resonance spectroscopy to noninvasively measure in situ intracellular-free magnesium levels in brain and skeletal muscle of fasting nonpregnant women (n=12), and of third trimester women with uncomplicated pregnancies (n=11) and preeclampsia (n=7). Compared with nonpregnant controls (brain 519±59 μmol/L; muscle 604±34 μmol/L), brain and skeletal muscle intracellular magnesium levels were significantly lower in both normal pregnant (brain 342±23 μmol/L; muscle 482±40 μmol/L; P=0.05 for both tissues) and preeclamptic women (brain 229±17 μmol/L; muscle 433±46 μmol/L; P=0.05 for both tissues). Brain intracellular magnesium was further reduced in preeclamptics compared with normal pregnant subjects (P=0.05). For all pregnant subjects, blood pressure was significantly and inversely related to the concomitantly measured intracellular magnesium level in brain (systolic, r=-0.59, P=0.01; diastolic, r=-0.52, P=0.02) but not in muscle. Cellular magnesium depletion is characteristic of normal pregnancy and may be one factor contributing to the pathophysiology of preeclampsia. Furthermore, the influence of central nervous system factors on blood pressure may be mediated, at least in part, by ambient intracellular magnesium levels.