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Division of Neonatology, Department of Pediatrics, University of Maryland Medical School, Baltimore, Maryland 21201
Both
glucocorticoids and alveolar fluid distension affect the rate of fetal
lung maturation, possibly representing a common cellular pathway. In an
explant culture, there is a spontaneous increase in triglyceride
incorporation into saturated phosphatidylcholine over time. This
mechanism is stimulated by prostaglandin (PG) E2, blocked by both bumetanide and
indomethacin, and overridden by exogenous
PGE2. Type II cells synthesized
and produced PGE2 between
days 16 and
21 postconception, increasing fourfold
between days 19 and
21. Fetal rat lung fibroblasts
released triglyceride in response to
PGE2, increasing 10- to 14-fold
between days 19 and
21 postconception; phloretin (1 × 10
5 M) completely
blocked this effect of PGE2 on
triglyceride release. Dexamethasone stimulated both type II cell
PGE2 synthesis (threefold) and
fibroblast triglyceride release in response to
PGE2 (60%) by
day 20 cells. Stretching type II cells
also increased PGE2 synthesis
(~100% at 1, 2, and 3 h vs. static cultures). Recombination of
[3H]triglyceride-labeled
fibroblasts with type II cells in an organotypic culture resulted in
progressive incorporation of label into saturated phosphatidylcholine
by type II cells. This process was also blocked by the addition of
indomethacin and overridden by exogenous
PGE2. These data suggest that the
combined effects of alveolar fluid dilatation and glucocorticoids may
coordinate the timely transfer of triglyceride from fibroblasts to type
II cells for augmented surfactant production through their effects on
PGE2 production and action as term
approaches.
stretch; surfactant; triglyceride
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