On the Mechanism of Renal Sodium Handling in Newborn Infants

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Abstract
In an attempt to delineate the specific tubular defect in sodium reabsorption in low-birth-weight neonates, fractional sodium excretion (CNa/Ccr), distal tubular sodium delivery (CNa+CH2O), and distal tubular sodium reabsorption [(CH2O/CH2O+CNa) × 100] were determined in 8 healthy premature and 10 full-term newborn infants. The mean birth weight was 1,701 g (range: 1,240–2,120 g) and the mean gestational age was 32.6 weeks (range: 28–35 weeks) for premature; and 3,199 g (range: 2,670–3,670 g) and 38.9 weeks (range: 38–41 weeks) for full-term neonates. It was demonstrated that the significantly higher fractional sodium excretion in premature infants (1.44 ± 0.33 SE versus 0.36 ± 0.09%, p < 0.01) resulted from significantly decreased proximal (CNa+CH2O: 0.674 ± 0.105 versus 0.360 ± 0.069 ml/min/1.73 m2, p < 0.05) and distal [(CH2O/CH2O+CNa) × 100:69.9 ± 3.3 versus 85.8 ± 3.4%, p < 0.01] tubular sodium reabsorption.