Growth retardation and the development of the respiratory system in fetal sheep

In an experimental model of fetal growth retardation which involves the reduction of placental mass in ewes, we have investigated the effects of intrauterine deprivation on aspects of structural development of the trachea and lungs of fetal sheep (140 days gestation). We have also measured the volume of luminal liquid aspirated from the lungs and the phospholipid content of this liquid as an index of pulmonary surfactant production. The effects of growth retardation are evident in the trachea where the structural development of the mucosal and submucosal layers has been affected. Abnormal aspects of development include the frequent lack of a ciliated border on epithelial cells in the mucosal layer and the reduction in the extent of the folds usually characteristic of this layer in near term fetal sheep. Although the fetal lungs are smaller in growth retardation (P < 0.01) they are appropriate for fetal weight and their structural development does not appear to have been retarded. In contrast, lung liquid volume is significantly reduced in relation to lung weight in growth retarded fetuses and the concentration of phospholipids in lung liquids is also reduced (P < 0.01).