Exudative lung injury is associated with decreased levels of surfactant proteins in a rat model of meconium aspiration.
OBJECTIVE
Meconium aspiration syndrome remains a common cause of respiratory failure in neonates. The acute effects of meconium aspiration are inactivation of lung surfactant in vivo and in vitro. This study investigated the delayed effects of meconium on alveolar surfactant phospholipids and protein levels in spontaneously breathing animals.


METHODS
Twenty-two adult rats were given 4.3 mg of dry weight human meconium after endotracheal intubation. Rats were briefly mechanically ventilated in room air, extubated, then killed after 16 (n = 6), 24 (n = 6), 48 (n = 6), and 72 hours (n = 4). Control animals received the same volume of normal saline (n = 7) or no meconium (n = 7). Bronchoalveolar lavage and tissue specimens were evaluated for inflammatory cells, total proteins, surfactant phospholipids, and surfactant proteins.


RESULTS
Meconium caused exudative lung injury that was reflected in increased cell counts and proteins in alveolar lavage fluid. The peak injury occurred at 16 hours after instillation, whereas recovery occurred by 72 hours. Although total lavage fluid phospholipids did not change over time, phospholipid and dipalmitoyl phosphatidylcholine in large aggregates tended to decrease at 24 hours. Western blot analysis demonstrated time-dependent qualitative decreases in surfactant proteins A and B (SP-A, SP-B) in meconium-instilled animals compared with the controls. ELISA for SP-B confirmed the Western blot findings with total SP-B in large aggregate decreasing from 25 +/- 4 microg in controls to 6.6 +/- 0.8 microg at 24 hours of injury.


CONCLUSIONS
Our study suggests that the exudative lung injury with meconium instillation is associated with decreased levels of SP-A and SP-B in the large aggregate fraction of lung surfactant. We speculate that decreased secretion and/or increased degradation accounts for lower levels of SP-B in bronchoalveolar lavage fluid.
Cleary
G M
GM
Division of Neonatal-Perinatal Medicine, Department of Pediatrics, Thomas Jefferson University and Hospital, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
Antunes
M J
MJ
Ciesielka
D A
DA
Higgins
S T
ST
Spitzer
A R
AR
Chander
A
A
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry* / Q000166:cytology; D004195:Disease Models, Animal; D006801:Humans; D007231:Infant, Newborn; D008171:Lung Diseases / Q000209:etiology / Q000473:pathology; D008297:Male; D008471:Meconium Aspiration Syndrome / Q000150:complications / Q000473:pathology*; D011510:Proteolipids / Q000032:analysis*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants