Perinatal anatomic development of alveolar type II cells in rats.

We studied the perinatal development of rat alveolar type II cells. The volume density (Vv) of lamellar bodies increased twofold from gestational day 21.5 to postnatal day 1 and 1.6-fold between age 1 and 60 days. The Vv of glycogen areas fell sharply between late gestation and postnatal day 1; this decrease was greater in pups delivered from dexamethasone- compared with diluent-treated dams. In utero administration of glucagon to fetuses on gestational day 21.5 caused a decline in the Vv of glycogen areas within 4 h. Pups from dams underfed in late gestation had a higher Vv of glycogen areas and a lower Vv of lamellar bodies on the first 2 postnatal days compared with pups from dams allowed food ad libitum. We conclude that rat alveolar type II cells are somewhat immature at birth; prenatal maternal underfeeding slows the pre- and postnatal maturation of alveolar type II cells; and 3) exogenous glucagon causes a fall in the Vv of glycogen areas in type II cells of fetal rats at gestational day 21.5.