Effect of intravenous phosphate on the red cell phosphate metabolites of the preterm infant

The effect of two different amounts of intravenous phosphorus (Pi) suppleme ntation on intracellular phosphorus (RBCPi) and 2,3 diphosphoglycerate (2,3 DPG) was studied in two groups of preterm newborn infants on total parente ral nutrition (TPN) during the first 7-10 days of life. Group A (n = 10) ne onates received 30 mg/kg/day and group B (n = 15) 60 mg/kg/day inorganic Pi intravenously. Sixteen preterm neonates who were fed with milk formula fro m day 2 (group C) were used as controls. Blood and spot urine specimens wer e collected on days 1,4, 7, 15 and 30 after birth. By the end of the first month of life, group B neonates had levels of plasma Pi (PlPi) higher than group A (5.69 +/- 0.8 mg/dl vs 4.71 +/- 0.3 mg/dl, p < 0.05) and comparable to the controls (5.9 +/- 0.7 mg/dl). Red blood cell Pi (RBCPi) increased i n group B infants after the fourth day of life and remained higher until th e end of the month when compared to the group A infants who received less p hosphate (2.34 +/- 0.8 mg/dl vs 1.36 +/- 0.3 mg/dl, p < 0.05). The 2,3 DPG levels were similar in group B and control infants all through the study pe riod, except on the 15th day. In group A infants 2,3 DPG levels were lower than in controls and on the 30th day they were also lower than in group B i nfants (4.63 +/- 0.7 in group A vs 6.48 +/- 1.3 in group B, p < 0.01 and 6. 54 +/- 1.1 mmol/l in controls, p < 0.01). A positive correlation was found between the concentrations of PlPi and RBCPi and 2,3 DPG levels for the stu dy groups together. Serum alkaline phosphatase (ALP) levels by the end of t he month were found increased in the neonates supplemented with lower phosp hate amounts (group A: 974 +/- 70 IU/L) than in group B (575 +/- 63 IU/L, p < 0.01) and controls (520 +/- 30 IU/L, p < 0,05). The beneficial effect of higher Pi supplementation on components of phosphate metabolism seems to l ast well beyond cessation of TPN. (C) 2001 Elsevier Science Inc. All rights reserved.