Short-term perinatal 10% O2 alters postnatal development of lung alveoli.

We studied the effect of breathing 10% O2 for less than or equal to 9 h by rat dams during the last day of gestation and (with their pups) for 1-2 h immediately after birth on the development of the lung's gas exchange region in the pups. Our major finding is that this brief stress resulted in substantially altered lung development noted at age 7 days and still partially present at age 30 days. In particular, perinatal hypoxia slowed the postnatal increase of lung volume, delayed septation of the large gas exchange saccules, diminished the increase of the gas exchange surface area, but accelerated thinning of the wall of the gas exchange structures. The changes produced by briefly breathing 10% O2 had as great an effect on these aspects of lung development as the same prenatal exposure to 10% O2 plus continuous postnatal exposure to 10% O2 for 7 days. Breathing 10% O2 had a particularly strong effect on alveolar wall thinning, since 2 h of breathing 10% O2 immediately after birth, without prenatal hypoxia, accelerated thinning of the alveolar wall.