A stereoscopic scanning electron microscope study of pulmonary hypoplasia in chondrodystrophic mice.

Pulmonary hypoplasia is a life threatening condition in newborns resulting from a generalized underdevelopment of the lungs. The lung disorder is usually secondary to conditions outside the lung such as thoracic volume reduction. The precise mechanism by which thoracic volume reduction prevents normal lung development and growth is unknown. As a model for human pulmonary hypoplasia associated with lethal skeletal dysplasia, a stereoscopic SEM study of chondrodystrophic (cho) fetal mouse lungs fixed by intratracheal instillation with 3% glutaraldehyde was conducted. In comparison with lungs of phenotypically normal littermates, the mutant's lungs appeared unaffected with respect to structure of major bronchiolar airways and in the morphology and amount of surfactant precursors (multilamellar bodies). The primary saccules within the mutant's lungs were significantly smaller and more numerous relative to those of normal littermates. These observations provide evidence that the lungs for this type of pulmonary hypoplasia are ultrastructurally normal with respect to upper airways, but that the primary saccules, or units of function in neonatal breathing in the rodent, are significantly smaller. This effect, however, does not appear to inhibit differentiation of type II pneumocytes or production of surfactant.