title: Postnatal development of alveoli. Regulation and evidence for a critical period in rats.
abstract: In many species, including humans, pulmonary alveoli are formed after birth by septal subdivision of the large gas-exchange saccules present at birth. In rats septation occurs mainly between the 4th and 14th postnatal days (Burri, P. H. 1974. Anat. Rec. 180:77-98), but little is known about the regulation of this process. We found that dexamethasone (0.1 micrograms daily) given to rats from age 4 to 13 d markedly impaired saccule septation to at least age 60 d and also diminished the extent of the increase of alveolar surface area (Sa). Underfeeding from birth to age 14 d did not diminish saccule septation but did result in diminished Sa. We conclude dexamethasone-treated rats have a critical period during which the gas-exchange saccules present at birth must be subdivided. Since Sa increased in dexamethasone-treated rats without a change in alveolar size, and, the enlargement of Sa was diminished in underfed rat pups without a deficit of saccule septation, we postulate new alveoli were formed by means other than septation of the large gas-exchange saccules present at birth. Furthermore, these various means of forming alveoli, and hence of increasing Sa, were differently regulated: dexamethasone decreased the enlargement of Sa brought about by both septation of the gas-exchange saccules present at birth and by other, as yet unidentified, means of forming alveoli; underfeeding did not diminish Sa increases produced by saccule septation but did decrease the extent of Sa enlargement due to the other means of forming alveoli.
mesh_terms: D000818:Animals; D001835:Body Weight; D004247:DNA / Q000032:analysis; D004261:DNA Replication / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D008098:Litter Size; D008176:Lung Volume Measurements; D008297:Male; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains / Q000254:growth & development
chemical_list: D003907:Dexamethasone; D004247:DNA