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NEONATAL SOCIETY ABSTRACTS

Increased sodium absorption across the nasal epithelium of ventilated moderately preterm infants on the first day of postnatal life

Presented at the Neonatal Society 2002 Summer Meeting (programme).

Gaillard EA, Shaw NJ, Wallace HL*, Subhedar NV, Southern KW*

Liverpool Women's Hospital, Neonatal Unit, Crown Street and *The Institute of Child Health, University of Liverpool, UK

Aims: To examine through the nasal potential difference (PD) profile, airway ion transport in moderately preterm infants (from 29 weeks gestation).

Background: Despite recent advances, lung disease following premature birth remains a significant clinical problem. Animal and clinical studies suggest that airway ion transport has a critical role in the adaptation to air breathing in postnatal life. In particular, sodium absorption mediated through the epithelial sodium channel (ENaC) is a major factor in lung water clearance after birth.(1) The a-ENaC subunit m-RNA expression has been found to increase with gestational age.(2) Immature airway ion transport as a result of prematurity may therefore contribute to the respiratory morbidity in infants born moderately preterm.

Methods: We studied 75 infants using a modified perfusion protocol suitable for neonates (healthy term infants n = 40; preterm 29-36 weeks gestation n = 35). We determined:
1.) Maximal baseline PD following perfusion of a physiological isotonic solution
2.) The change in PD following perfusion with amiloride 10-4 M (?amil, to assess ENaC activity)
3.) The change in PD, after perfusion with a solution low in Cl- (to assess the capacity for Cl- secretion).

Results: Maximal baseline PDs are shown in graph 1. Four ventilated infants had maximal baseline PDs greater than -50mV. Amiloride perfusion resulted in substantial reduction in PD magnitude (median ?amil in pretem, 80%) and there was little capacity for chloride secretion in either cohort.

□: ventilated male infants; ■: non-ventilated male infants
∆: ventilated female infants; ▲: non-ventilated female infants

Conclusion: This is the first reported clinical study examining the postnatal airway ion transport pattern in moderately preterm infants and these data suggest these processes are well developed in these infants on day 1 of postnatal life. The findings support a normal switch from the fetal secretory pattern to a fluid absorptive state after birth in this cohort, similar to term infants. We found increased nasal PD in some ventilated preterm infants after birth. ?amil in these infants confirms that the increased PD principally reflects ENaC-mediated sodium absorption. The sodium hyperabsorption evident in some of the ventilated preterm infants may reflect a compensatory mechanism to clear fluid from the lungs.

References
1. Hummler E, Barker P, Gatzy J, Beermann F, Verdumo C, Schmidt A, Boucher R, Rossier BC. Nature Genetics 1996;12:325-8.
2. Tchepichev S, Ueda J, Canessa C, Rossier BC, O'Brodovich H. American Journal of Physiology 1995;269:C805-12

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