Ionized magnesium and gestational age.

OBJECTIVE: Investigation of magnesium (Mg) homeostasis has re-emerged as an area of interest in preterm born neonates who are at risk for brain pathology. However, data regarding the association between the biologically active ionized form of Mg and gestational age (GA) at an early stage of life in newborn infants are controversial. METHODS: We evaluated the total and ionized Mg electrolyte (TMg and IMg) as well as the calcium (TCa and ICa) and pH in the cord blood and on day 2 of life in 22 neonates born at different gestational ages (< 32, 32-34 and > or =35 week) without magnesium tocolysis and absence of serious complications during pregnancy and delivery. RESULTS: The IMg fraction that accounted for 68.1+/-5.1% of the TMg in the cord blood and 67.9+/-4.5% of the TMg on day 2 of life, was significantly higher in very preterm infants (GA< 32 week) as compared to neonates with GA > 35 week. Higher IMg levels were correlated with the lower pH that was recorded in the cord blood of the very preterm infants (correlation coefficient, r=-0.80, p< 0.0001) and ICa (r = -0.52, P< 0.01). Lower pH also was correlated with the GA (P< 0.0001). However, standard multiple regression analysis showed significant association between IMg levels and decreased pH but not the gestational age or ICa (beta=-1.10+/-0.21, p< 0.00009). CONCLUSION: Extremely preterm infants even without additional exposure to tocolytic magnesium are at risk for the lower pH associated elevation of ionized Mg, which should be considered during the management of these infants in order to prevent hypermagnesemia-related pathology.

Effect of metabolic control on parathyroid hormone secretion in diabetic patients

The metabolic derangement caused by diabetes mellitus may potentially affect bone mineral metabolism. In the present study we evaluated the effect of diabetes metabolic control on parathyroid hormone (PTH) secretion during stimulation with EDTA infusion. The study was conducted on 24 individuals, 8 of them normal subjects (group N: glycated hemoglobin - HbA1C = 4.2 + or - 0.2 percent; range = 3.5-5.0 percent), 8 patients with good and regular metabolic control (group G-R: HbA1C = 7.3 + or - 0.4 percent; range = 6.0-8.5 percent), and 8 patients with poor metabolic control (group P: HbA1C = 12.5 + or - 1.0 percent; range: 10.0-18.8 percent). Blood samples were collected at 10-min intervals throughout the study (a basal period of 30 min and a 2-h period of EDTA infusion, 30 mg/kg body weight) and used for the determination of ionized calcium, magnesium, glucose and intact PTH. Basal ionized calcium levels were slightly lower in group P (1.19 + or - 0.01 mmol/l) than in group N (1.21 + or - 0.01 mmol/l) and group G-R (1.22 + or - 0.01 mmol/l). After EDTA infusion, the three groups presented a significant fall in calcium, but with no significant difference among them at any time. Basal magnesium levels and levels determined during EDTA infusion were significantly lower (P<0.01) in group P than in group N. The induction of hypocalcemia caused an elevation in PTH which was similar in groups N and G-R but significantly higher than in group P throughout the infusion period (+110 min, N = 11.9 + or - 2.1 vs G-R = 13.7 + or - 1.6 vs P = 7.5 + or - 0.7 pmol/l; P<0.05 for P vs N and G-R). The present results show that PTH secretion is impaired in patients with poorly controlled diabetes