The role of magnesium in neonatal calcium homeostasis: effects of magnesium infusion on calciotropic hormones and calcium.

Abstract

Magnesium (Mg) deficiency is a possible etiologic factor contributing to neonatal hypocalcemia. In adults, parathyroid hormone (PTH) secretion is negatively feedback regulated by acute changes in serum Mg concentration, but paradoxically Mg deficiency may lead to functional hypoparathyroidism and hypocalcemia. We hypothesized that in neonates, Mg administration will cause changes in PTH secretion and serum Ca concentration that will be inversely related to serum Mg status. We also hypothesized that Mg administration will result in increased calcitonin (CT) secretion. Thirty-nine newborn infants with birth weights greater than 1500 g were studied on day 3 of life. Ten received placebo, and 29 intravenous magnesium sulfate (MgSO4), 6 mg elemental Mg/kg body weight, over 1 h. Serum Mg, Ca, PTH, and CT were measured at time 0 (baseline, preinfusion) and 1, 2, 6, 12, 24, and 48 h postinfusion. In both groups combined, baseline PTH correlated with baseline Mg (r = 0.72, p less than 0.005), and with baseline Ca (r = 0.68, p less than 0.005). In the control group there was no change in serum Mg, Ca, PTH, and CT during the study period. In magnesium sulfate-infused infants: 1) serum Mg concentration rose from 1.80 +/- 0.06 to 2.82 +/- 0.07 mg/dl (mean +/- SEM, p less than 0.001); 2) the change from baseline in serum PTH at 1, 6, and 12 h postinfusion correlated inversely with baseline Mg (p less than 0.05); 3) the change from baseline in serum Ca at 1, 2, and 24 h postinfusion correlated inversely with baseline Mg (p less than 0.005); 4) serum CT remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)