Development of bronchiolar epithelium in rats.

We used ultrastructural and morphometric means to examine aspects of the regulation of the maturation of rat bronchiolar Clara cells and the development of the epithelium of small conducting airways in the perinatal period. We found the nuclear numerical density per cubed centimeter (Nvn) of Clara cells fell and the Nvn of ciliated cells increased from birth to age 60 days, the prenatal administration of a glucocorticosteroid (dexamethasone) to dams caused a 35% decrease in the Nvn of ciliated cells present at birth but did not alter the Nvn of Clara cells, the administration of dexamethasone to pups from postnatal days 1 to 6 did not alter the Nvn of bronchiolar Clara or ciliated cells present at age 7 days but did diminish the total number of lung cells as assessed by measurements of lung DNA, the administration of dexamethasone to dams from gestation days 18 to 20 or from gestation days 20 to 22 did not alter the volume density of Clara cell glycogen, secretory granules, rough endoplasmic reticulum, or mitochondria of pups at gestation day 21.5 or on the day of birth, and glucagon, epinephrine, and 8-bromoadenosine 3',5'-cyclic monophosphate resulted in a decrease of Clara cell glycogen when individually incubated in vitro for 4 h with bronchiolar tissue from rat fetuses 21.5 days of age.