Abstract 1856 Poster Session IV, Tuesday, 5/4 (poster 317)

Fetal tracheal obstruction (TO) can reverse the lung hypoplasia associated with experimental congenital diaphragmatic hernia through its ability to induce massive lung growth. The histology of these lungs shows an increase in alveolar number, normal vascularization, but a dramatic decrease in the number and the function of type II cells. Previous studies in fetal sheep have shown that the rate of lung growth, as measured by DNA incorporation of [3H]-thymidine, is maximale after 3 d of TO and is not different from controls after 10 d. RNA levels of insulin growth factors 1 and 2 (IGF-1 and -2) have been shown to increase after prolonged TO. In this study, we examined cell specific of IGF-1 mRNA after a short occlusion period in fetal sheep. At 113-120 d of gestation, cannulas were implanted 2-4 cm into the trachea and joined externally to form a tracheal loop that allowed flow of lung fluid. From 125 to 128 d, the trachea was either occluded by clamping the catheter (TO group, n=5) or the fluid was allowed to flow through (control group, n=5). IGF-1 mRNA expression was studied by in situ hybridization using a [33P]-labeled riboprobe. In the control group, slight expression of IGF-1 was seen around some blood vessels. In contrast, in the TO group, intense signal was consistently observed over the smooth muscle cells of medium size arteries. Because the pattern of IGF-1 expression resembled the distribution of transforming growth factor beta (TGF-β) during lung development, TGF-β2 mRNA expression was also studied. In the control group, TGF- β2 was occasionally observed over the epithelium of airways. After TO, TGF- β2 expression decreased in airways while it increased abundantly in the alveolar epithelium. The intense IGF-1 expression in the smooth muscle cells of blood vessels must be related to the rapid growth of that tissue which accompanies airway development. TGF- β2 expression is probably related to alveolar growth yet its negative effect on type II cell differentiation may account for decrease number of type II cells and the surfactant deficiency observed after TO.

Support: Canadian MRC, FRSQ and Foundation de la recherche sur les maladies infantiles