Effect of prenatal glucocorticoids on pulmonary vascular muscularisation in nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND/
PURPOSE: Pulmonary hypertension (PH) contributes significantly to the mortality of congenital diaphragmatic hernia (CDH). Pulmonary vascular changes in CDH include a reduced vascular bed with increased arterial medial wall thickness and peripheral extension of muscle into intraacinar vessels. Antenatal steroids improve biochemical immaturity, lung compliance, and morphology in experimental CDH animals. The aim of this study was to examine the effects of prenatal glucocorticoid therapy on pulmonary artery muscularisation in CDH rats.
METHODS: CDH was induced in fetal rats by the maternal administration of 100 mg of nitrofen by gavage on day 9.5 of gestation (term, day 22). Control animals received olive oil (OO). Dexamethasone (Dex, 0.25 mg/kg) or normal saline (NS) was given by intraperitoneal injection on days 18.5 and 19.5, and fetuses were delivered by caesarean section on day 21.5. Lung sections from five fetuses in each of four experimental groups were studied by a blinded investigator- OO-NS controls, CDH-NS, CDH-Dex, and non-CDH-NS. The external diameter (ED), medial wall thickness (MT), percent of medial wall thickness, and wall structure were evaluated from preacinar arteries accompanying conducting airways, and the intraacinar arterioles associated with the respiratory bronchi and saccules.
RESULTS: In the preacinar arteries, CDH-NS animals had a significantly increased MT percentage compared with OO-NS controls (21.2+/-8.8 v 17.8+/-10.3, P = .0001). CDH-Dex rats had a lower MT percentage than CDH-NS rats (15.5+/-6.7 v 21.2+/-8.8, P = .0001). In the intraacinar region, CDH-Dex fetuses had a reduced percentage of muscularised intraacinar blood vessels compared with CDH-NS and OO-NS controls (10% v 24% and 28%, respectively, P = .01). Dexamethasone-treated CDH pups also displayed a significantly lower MT percentage of the intraacinar arteries compared with CDH-NS and OO-NS animals (15.7+/-13 v 23.4+/-9 and 25.4+/-12, P = .003).
CONCLUSIONS: Medial hypertrophy is present in the preacinar but not the intraacinar blood vessels of CDH rats before birth. Dexamethasone inhibits medial hypertrophy and reduces the number of muscularised intraacinar vessels. Antenatal glucocorticoids may reduce the risk of PH developing in human newborns with antenatally diagnosed CDH.