Perinatal cellular ion metabolism: P-nuclear magnetic resonance spectroscopic analysis of intracellular free magnesium and pH in maternal and cord blood erythrocytes
We sought to establish and compare the distribution of intracellular and extracellular magnesium and pH in cord and maternal erythrocytes at the time of delivery. We used 31P-nuclear magnetic resonance spectroscopy and a magnesium-specific ion-selective electrode apparatus to evaluate plasma and intracellular red cell content of free magnesium, pH, and ionized calcium in blood obtained from cord and corresponding maternal samples. Cord erythrocyte intracellular free magnesium content (110 +/- 4 mumol/L) and pH (7.02 +/- 0.01) were lower than corresponding maternal intracellular values (140 +/- 9 mumol/L, P < .05; and 7.20 +/- 0.02, P < .0005, respectively). The extracellular cord ionized magnesium concentration in plasma was closely related to the intracellular free magnesium concentration (r = 0.71, P < .005). Extracellular ionized magnesium and calcium were both greater in cord than in maternal samples (P < .05 and P < .0005, respectively). These data indicate a differential distribution of extracellular and intracellular magnesium and pH in cord versus maternal blood cells. We hypothesize that these deviations are physiological and may serve to maintain tissue oxygen delivery, while at the same time mediating the changes in vascular tone characteristic of birth.