Cell proliferation and apoptosis in experimental lung hypoplasia

Background/Purpose: Current treatment for lethal pulmonary hypoplasia in co ngenital diaphragmatic hernia (CDH) may be hampered by uncertainty over its origin. Herniation of abdominal organs into the chest was thought to produ ce lung hypoplasia by compression. Experimental CDH models suggest that dis turbed lung growth precedes these events. Mammalian development comprises c ell differentiation, proliferation and programmed cell death or apoptosis, Could lung hypoplasia in CDH result from alterations in these processes wel l before visceral herniation takes place? The aim of this study was to comp are cell proliferation and apoptosis in normal and hypoplastic embryonic lu ngs before normal diaphragmatic closure using a CDH model. Methods: Sprague-Dawley rats were given 100 mg of nitrofen on day 9.5 of pr egnancy to create lung hypoplasia and CDH in newborns (term, 22 days). Cont rol rats received olive oil. Cell proliferation in embryonic lung specimens was measured by bromodeoxyuridine (BrdU) incorporation at 13.5 to 15.5 day s' gestation, before normal diaphragmatic closure in this species (day 16.5 ). Apoptosis was measured by the in situ end-nick labelling (TUNEL) method in lung sections obtained from rat embryos of 13.5 to 16.5 days' gestation. Results: High levels of cell proliferation were seen in both normal control and nitrofen-exposed lungs. However, 24 hours before normal diaphragmatic closure, nitrofen-exposed lungs had significant reductions in cell prolifer ation on day 15.5 of gestation (P = .009 vcontrols). Apoptosis occurred at low levels throughout the developmental stages examined (10.3%) without sig nificant differences encountered between the study groups. Conclusions: These findings have shown high rates of cell division during n ormal lung development before diaphragmatic closure. Decreased levels over this critical period in gestation may contribute to early lung anomalies in the nitrofen CDH model. Strategies to promote cell proliferation in the fe tal lung may therefore hold future promise in human CDH. Apoptosis appears not to play a major role in hypoplastic lung development. Therapies to inhi bit apoptosis would seem unlikely to improve this early lung growth.