Fetal Homeostasis in Maternal Malnutrition. II. Magnesium Deprivation

Abstract

ExtractIn rats, supplied with an adequate dietary intake of magnesium, the mean fetal magnesium concentration in plasma was 2.4 mEq/liter compared with a maternal concentration of 1.6 mEq/liter. Equilibrium dialysis experiments resulted in a disappearance of the fetal to maternal gradient, with maternal levels becoming slightly higher than fetal levels. Determination of ultrafiltrable magnesium concentrations also demonstrated a slightly lower binding capacity for magnesium in fetal plasma so that the fetal to maternal gradient reflected the unbound magnesium.When a diet containing magnesium in a concentration of 0.88 mEq/kg (compared with a control diet containing 120 mEq/kg) was introduced on day 2 of gestation, only one of eight pregnant rats bore a litter to term. If the diet was introduced on day 10 of gestation, pregnancy continued until term but there was an increased resorption rate and the surviving fetuses were small, weak, and anemic. Analyses of maternal muscle for magnesium, calcium, sodium, and potassium revealed normal concentrations, even though magnesium concentrations in plasma rapidly fell to 20% of the normal level. There appeared to be a reduction in bone magnesium. The significant changes in the fetus were a reduction in magnesium levels in plasma with a disappearance of the fetal to maternal gradient and an elevation in sodium levels. Analysis of the total fetus demonstrated a reduction in magnesium and potassium and an increase in calcium concentrations. The last was also evident in the placenta. Speculation"Fetal parasitism" as a general concept appears to be. an over-simplification which can be denned with accuracy only by the study of deprivations of specific nutrients, and eventually by the interaction of such nutrients.

Evidence for Active Maternofetal Transfer of Magnesium across the in Situ Perfused Rat Placenta

“…Lowered plasma Mg concentrations have been reported previously in pregnant rats (1) and rabbits (3), the latter study suggesting that this may partly reflect maternofetal Mg transfer. Studies in humans, however, suggest that a decrease in maternal plasma Mg concentration during pregnancy is related to a dilutional process inasmuch as plasma protein and Mg concentrations were correlated (14).…”

Effect of chronic maternal dietary magnesium deficiency on placental calcium transport.

“…Even a threefold decrease in ma ternal serum Mg concentrations failed to significantly af fect placental Ca transport. One reason may be that de pendence of the placental Ca ATPase on Mg may not have been affected if intracellular Mg concentrations were pre served at the expense of serum concentrations [26]. Alter natively, we suggest that this noninteraction is the result of the possible presence of two independent transporters for the two ions, similar to that hypothesized for intestinal Ca transport.…”

A role for magnesium in neonatal parathyroid gland function?

“…Transfer of Mg from mother to fetus ap pears to be an active ATPase-dependent transport process [30]. However, in maternal Mg deficiency the mother may maintain a normal intracellular Mg concentration while her fetus will be Mg-deficient [31]. Mg, with its integral role in the secretion and function of PTH, may have a permissive role in the newborn's PTH response to falling serum CA concentrations.…”