Vascular to alveolar leak of iron dextran (120 kD) in the immature ventilated rabbit lung

Rabbit fetuses were delivered by hysterotomy on day 27 or 28 of gestation. Immediately after birth, the animals were tracheotomized and received by intravenous injection 0.2 mu Ci radiolabeled albumin and 11 mg iron dextran in 0.2 ml saline. The newborn rabbits then were ventilated artificially with a tidal vol of 12 ml/kg for 5-20 min. One group of nonventilated animals served as controls. At the end of the experiment, one lung was lavaged via the airways and the other was fixed for histologic examination. The recovery of labeled albumin and iron dextran in the lavage fluid was quantified. Iron dextran complexes were easily identified in the lung sections by staining with Prussian blue. Iron dextran accumulated in the airspaces of animals delivered on day 27 (about 4% of the injected dose during 10-20 min of ventilation). The albumin leakage was slightly higher than that of the dextran, a result consistent with different mol wt of the markers. The vol density of leaking alveoli in histologic sections increased with time, from 0 at birth to a mean value of 0.36 after 20 min of ventilation. The leakage starts as a focal event, gradually involving more and more terminal airspaces. In the histologic sections, there was no indication of a significant leakage at the bronchiolar level, although the epithelium of terminal and preterminal airways was clearly injured in all ventilated animals.