Ultrastructural features of alveolar epithelial cells in the late fetal pulmonary acinus: A comparison between normal and hypoplastic lungs using a rat model of pulmonary hypoplasia and congenital diaphragmatic hernia

Abstract

The aim of this study was to describe and compare the ultrastructural features and functional maturity of alveolar epithelial cells in hypoplastic and normal fetal rat lungs. Pulmonary hypoplasia in association with congenital diaphragmatic hernia was induced in fetuses by administration of 2,4-dichlorophenyl-p-nitrophenylether (Nitrofen) to pregnant Sprague Dawley rats (100 mg on day 10 of gestation). Lung tissue of Nitrofen-exposed and control fetal rats aged 19-22 days (vaginal plug day 1, birth day 23) was embedded in Epon. Semithin (1 micron) toluidine blue-stained sections were examined by light microscopy; ultrathin sections (approximately 80 nm) were studied via transmission electron microscopy. In bronchoalveolar lavage fluid from control and Nitrofen-exposed fetuses (day 22), phospholipid fractions and surfactant protein A content were measured semiquantitatively. On day 19 both control and Nitrofen-exposed lungs contained only cuboid alveolar epithelial cells; from day 20 there were cuboid, low cuboid, and thinner epithelial cells. The (low) cuboid cells contained large glycogen fields, some precursory stages of multilamellar bodies (MLBs), and just a few mature MLBs on day 19 and 20; smaller glycogen fields, more precursory stages, and more mature MLBs on day 21; and little or no glycogen but many precursory stages and mature MLBs on day 22. The thinner cells contained little or no glycogen and a few precursory stages of MLBs on days 20-22; very thin cells on day 22 contained neither glycogen nor any precursory stages of MLBs. MLBs and tubular myelin were seen in the lumens of future air spaces from day 20 onward. Nitrofen-exposed lungs differed from control lungs in that inclusion bodies (IBs) were less numerous in (low) cuboid alveolar cells on days 19 and 20, and more glycogen was seen on day 22. In addition intra- and extracellular "MLBs" in exposed lungs more often had an unusual appearance, i.e., a confluent structure and higher electron density. However, despite morphologic differences, there was no clear difference in phospholipid composition and SP-A content per mol phospholipid in bronchoalveolar lavage fluid. We conclude that morphologically hypoplastic lungs are less mature near term, without an apparent effect on surfactant composition.

Expression and Activity of Matrix Metallo Proteinases 2 and 9 and Their Inhibitors in Rat Lungs During the Perinatal Period and in Diaphragmatic Hernia

“…Since the lungs in CDH have thicker septa, are more compact and have altered collagen and elastin levels [2,13,14], we speculated that MMP/TIMP levels in the hypoplastic lungs would be altered in comparison to normal lung tissue levels.…”

Impaired VEGF and nitric oxide signaling after nitrofen exposure in rat fetal lung explants

“…When a maternal rat or mouse is fed nitrofen at precise time points of lung embryogenesis (E9.5 in rats, E8.5 in mice), the fetus often develops features of CDH that include bilateral lung hypoplasia, with more severe changes on the left lung, and in many cases, diaphragmatic defects (6,14,23,25,35,50). Nitrofen exposure induces small lungs with reduced airway branching and septation, thickened interstitium, and reduced vascular density (10,35). Interestingly, abnormal lung growth has been shown to precede the normal timing of diaphragm closure, suggesting that pulmonary hypoplasia is at least partly due to a direct teratogenic insult (14,25).…”

Pulmonary Surfactant Protein A, B, and C mRNA and Protein Expression in the Nitrofen-Induced Congenital Diaphragmatic Hernia Rat Model

“…It has to be kept in mind that a secondary surfactant deficiency may develop due to the negative effects of artificial ventilation on surfactant function after birth (21). So far, data from human and different animal CDH models (22) failed to report consistent results concerning the surfactant status in CDH (summarized in Table 1) (17)(18)(19)(20)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39).…”