Objective: In the newborn infant, removal of fetal lung liquid from the airways depends on ion transport through the airway epithelium. The epithelial sodium channel is considered rate limiting for the postnatal clearance of lung liquid, but it is unknown whether during the early postnatal period the expression of epithelial sodium channel is associated with maturity. Our objective was to study the relationship between gestational age and epithelial sodium channel expression in airway epithelium.
Methods: In 90 newborn infants (preterm [gestational age < 37]: n = 29; term [gestational age > or = 37]: n = 61), we measured the expression of epithelial sodium channel (reported as attomoles of subunit expression normalized to femtomoles of expression of cytokeratin 18) in nasal epithelium at 1 to 5 and 22 to 28 hours after birth.
Results: At 1 to 5 hours postnatally, airway expression of alpha-, beta-, and gamma-subunits of epithelial sodium channel was lower in preterm than in term infants. At this time point, significant correlations existed between gestational age and airway expression of alpha- and beta-epithelial sodium channel. By 22 to 28 hours after birth, only the expression of beta-epithelial sodium channel had decreased significantly in the preterm infants, whereas the expression of all epithelial sodium channel subunits had decreased significantly in the term infants. At this time point, no difference in expression of any of the subunits was found between preterm and term infants.
Conclusions: Airway expression of epithelial sodium channel at 1 to 5 hours of age is significantly lower in preterm than in term infants. Low postnatal expression of alpha-, beta-, and gamma-epithelial sodium channel subunits in the airway epithelium may contribute to the development of respiratory distress in the preterm infant.