Pulmonary epithelial liquid absorption, expressed in relation to alveolar surface area, is reduced in fetal lambs following in utero tracheal occlusion

We examined the effect of accelerated lung growth, induced by in utero tracheal occlusion (TO), on lung liquid uptake in near-term fetal sheep. In utero TO was performed in five fetal sheep at 110 days of gestation (term, approximately 145 days); six SHAM operated fetuses served as controls. The rate of liquid movement across the pulmonary epithelium was measured, using a previously established technique, in anesthetized fetal sheep between 133-137 days of gestation during a 2-hr adrenaline infusion (0.50 microg/min/kg, I.V.) and while lung luminal pressure was maintained at 5 mmHg. The rate of fetal lung liquid uptake was linear in all fetuses (mean r(2) < 0.97, n = 11). Mean values of lung liquid uptake expressed in relation to dry lung weight and luminal surface area of the right lung were significantly lower in TO fetuses (1.8 +/- 0.3 mL/hr/g and 1.0 +/- 0.2 mL/hr/m(2)) than in SHAM fetuses (2.6 +/- 0.2 mL/hr/g and 1.8 +/- 0.1 mL/hr/m(2)); surface area of the right lung was 140% greater in TO fetuses than in SHAM fetuses. There was a linear relationship between lung liquid uptake and pulmonary epithelial surface area in SHAM animals, but not in TO fetuses. We hypothesize that loss of alveolar epithelial type-II cells induced by increased levels of fetal lung expansion may impair alveolar liquid clearance in the perinatal period.