) Pulmonary edema is a common cause of acute and chronic respiratory failure after premature birth. Protein-rich liquid enters the airspaces as a result of vascular and epithelial injury in lungs that are not yet fully developed. The major driving force for postnatal removal of liquid from the airspaces into the pulmonary circulation is active Na transport across the respiratory epithelium. Previous work with lungs from fetal and newborn rabbits suggested that abnormal Na-K-ATPase activity in the respiratory tract epithelium might slow liquid clearance from the lungs after premature birth. It is unknown how postnatal lung injury affects these processes, nor is it known how these processes operate to regulate lung liquid clearance after birth either in human infants or in non-human primates. The purpose of this project is to determine the effects of acute and chronic lung injury on ion transport in epithelial cells derived from the trachea and terminal air sacs of premature baboons, and to see how these effects influence liquid absorption from the lung lumen. This project takes advantage of a unique animal model of neonatal lung injury after premature birth in non-human primates that are delivered by cesarean section and treated with mechanical ventilation for up to 3 weeks after birth.
Specific aims focus on the central hypothesis that absorption of liquid from the airspaces of the developing lung is driven by active Na transport across the respiratory tract epithelium, a process that is impaired after premature birth and subsequent lung injury induced by mechanical ventilation with oxygen enriched gas. The project uses complementary experimental approaches to study birth-related changes in respiratory epithelial ion transport and liquid movement, and the influence of postnatal lung injury on these processes: (1) airway and distal lung epithelial cells will be isolated from fetal and newborn baboons in order to measure fluxes of radiolabeled ions (86Rb, 36CJ, 22Na) in the presence or absence of various inhibitors of ion transport; (2) molecular techniques will be used to measure MRNA for the cc, and B, subunits of Na-KATPase and to quantify Na-K-ATPase protein abundance in tracheal and distal lung epithelial cells; (3) immunohistochemistry and in situ hybridization will be used to localize Na-K-ATPase and Na and Cl channels on respiratory epithelium of fetal and newborn baboons with and without postnatal lung injury; and (4) excised lungs will be used to measure net production (secretion and absorption) of luminal liquid under basal and experimental conditions (with and without preceding injury, treatment with glucocorticoids before birth, and treatment with surfactant). This investigation should provide new insight into the possible role of pulmonary epithelial dysfunction in the pathogenesis of lung edema that often occurs in newborn infants with acute and chronic respiratory distress syndromes.
