ALVEOLAR EPITHELIAL COMPOSITION AND ARCHITECTURE OF THE LATE FETAL PULMONARY ACINUS - AN IMMUNOCYTOCHEMICAL AND MORPHOMETRIC STUDY IN A RATMODEL OF PULMONARY HYPOPLASIA AND CONGENITAL DIAPHRAGMATIC-HERNIA

The aim of the present study was to compare the architecture and alveo lar epithelial cell composition of the pulmonary acinus in hypoplastic and normal fetal rat lungs. For this purpose, a rat model of pulmonar y hypoplasia in association with congenital diaphragmatic hernia (CDH) induced by Nitrofen (100 mg on day 10 of pregnancy) was studied. Sect ions (5 mu m) from lungs of control and Nitrofen-exposed fetal Sprague Dawley rats with or without CDH aged 18-22 days (vaginal plug on day 1, birth on day 23) were stained with hematoxylin and eosin. To identi fy developing alveolar epithelial cells, sections were incubated with anti-surfactant protein A (SP-A; rabbit anti-mouse) or preimmunization serum (indirect immunofluorescence). On days 18 and 19, control lungs and exposed lungs from fetuses with and without CDH looked similar (p seudoglandular stage of lung development). The prospective pulmonary a cinus consisted of acinar tubules with small round lumens, lined by cu boid, fluorescent type II cells. Morphometric analysis on day 19 showe d significantly smaller lung volumes and lung tissue volumes after Nit rofen exposure. On day 20 (canalicular stage), some tubules were sligh tly dilated and lined by cuboid and thinner fluorescent cells; these d ilated tubules were less numerous in lungs from exposed fetuses with C DH. On days 21 and 22 (saccular stage), the saccular lining consisted of cuboid to thin fluorescent cells in exposed lungs from fetuses with and without CDH, and fluorescent (low) cuboid cells interspersed with dark zones (type I cell areas) in control lungs. In the exposed lungs from fetuses with CDH, the lumens of all airspaces were frequently sl it-like, and the septa were thicker. These phenomena gave the lungs a primitive, compact aspect. Morphometric analysis on day 22 showed smal ler lung volumes and lung tissue volumes, smaller airspace/tissue rati os, smaller epithelial surface areas, and more type II cells per surfa ce area in Nitrofen-exposed lungs than in normal control lungs. The re sults suggest that Nitrofen-exposed, and thus hypoplastic, fetal rat l ungs are retarded with respect to the differentiation of cuboid type I I cells into squamous type I cells whether or not CDH is present, and with respect to the development of the future airspaces between days 2 0 and 22 if CDH is present.