Antenatal Dexamethasone Administration Increases Fetal Lung DNA Synthesis and RNA and Protein Content in Nitrofen-Induced Congenital Diaphragmatic Hernia in Rats

Abstract

Antenatal glucocorticoids treatment has been shown to correct pulmonary immaturity. The thymidine analog bromodeoxyuridine (BrdU) is incorporated into S-phase cells and used as a marker of DNA synthesis. In this study, we investigated the effect of antenatal glucocorticoid administration on DNA synthesis and RNA and protein content in nitrofen-induced congenital diaphragmatic hernia (CDH) in rats to better understand the effect of antenatal glucocorticoids on CDH lung. The CDH model was induced in pregnant rats using nitrofen. Dexamethasone (0.25 mg/kg) was given on d 18.5 and 19.5 of gestation (term ϭ 22 d). BrdU was administered 1 h before fetuses were killed on d 21, and detected by immunohistochemistry. DNA synthesis was evaluated by percentage of BrdU-incorporated nuclei (BrdU labeling index). Total RNA and soluble protein were extracted from another set of left lungs to measure RNA and protein content. BrdU labeling index and total RNA content were significantly decreased in CDH lung compared with control rats. Antenatal dexamethasone treatment significantly increased BrdU labeling index and RNA and protein content in the left CDH lung. Our findings of decreased DNA synthesis and decreased RNA and protein content in CDH lung suggest that lung growth and development are suppressed in hypoplastic CDH lung. Increased DNA synthesis and increased RNA and protein content in dexamethasone-treated CDH lung suggest that antenatal glucocorticoids may accelerate fetal lung growth and development in CDH. The high mortality in patients with CDH has been shown to be the result of pulmonary hypoplasia and persistent pulmonary hypertension (1). Although newer treatment modalities, including high-frequency ventilation, extracorporeal membrane oxygenation, surfactant therapy, and nitric oxide inhalation, have been introduced in an attempt to improve survival in patients with CDH, the mortality in this condition still remains high (1, 2).Recent improvements in antenatal sonography have resulted in a large number of CDH cases being diagnosed antenatally (3), which provided a possibility of antenatal treatment for severe CDH patients. Recently, antenatal administration of glucocorticoid has been proposed as a noninvasive modality in promoting fetal lung maturation and differentiation. Several control trials have shown the beneficial effects of antenatal glucocorticoid therapy as a means of promoting lung maturation and preventing respiratory distress syndrome in premature human newborns (4, 5). In experimentally produced CDH in animals, it has been reported that antenatal glucocorticoid treatment improves surfactant biochemical immaturity, increases lung compliance and distensibility, enhances lung morphology, and reduces pulmonary vascular adventitial and medial thickness (6 -11). The exact mechanism by which antenatal glucocorticoid therapy improves pulmonary immaturity in CDH is not fully understood.BrdU is a thymidine analog that is incorporated into the newly replicated DNA of S-phase cells. Since an antibody specific for...

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