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Developmental aspects of lung lipids.

From this review, it is evident that multiple maternal/fetal endogenous or completely exogenous factors have been associated with the complex process regulating fetal lung development. Recent in vitro experiments with human fetal lung explants are especially noteworthy and may establish a perspective for future research. Snyder et al (108) and Medelson et al (74) have found that lung explants from 16-22-week abortuses show differentiated type II cells and augmented PC synthesis within 4 days of culture, rather than the minimum 10- to 15-week period expected in utero. Such a phenomenon is reminiscent of the usual time for clinical recovery from uncomplicated RDS (34). Thus, although expression of the genes influencing lung surfactant phospholipid synthesis and related biochemical processes normally occurs relatively late in gestation, the potential for biochemical differentiation is clearly present in earlier stages. It appears then that the "programming" of the fetal lung for maturation is not absolute but may be altered under certain influences. Whether the advent of lung biochemical maturation occurs as a result of release from inhibition, as the human lung explant data imply, or occurs in response to stimuli, as suggested by exogenous corticosteroid effects, remains to be clarified and is a very challenging scientific problem. It will also be of great interest to define further other biochemical regulators, such as fibroblast pneumocyte factor, that may play an important role in fetal lung maturation.