The developing rat lung fibroblast and alveolar type II cell actively recruit surfactant phospholipid substrate.

Timely, adequate production of pulmonary surfactant is critical for survival at birth. This process is dependent on both maternal nutrition and glucocorticoids. Fetal rat lung lipofibroblast triglyceride accumulation is saturable, temperature-dependent and stimulated by glucocorticoids and cyclic AMP in primary cell culture. Spontaneous triglyceride uptake by fibroblasts increases ninefold between 17 and 21 days (= term) gestation and is stimulated 30-80% by exogenous glucocorticoid treatment. Coculture of Type II cells with fibroblasts preloaded with 3H-trioleate and increasing amounts of triglyceride results in a concomitant increase in saturated phosphatidylcholine (SPC) synthesized by Type II cells. Dexamethasone stimulates mobilization of fibroblast triglyceride incorporation into Type II cell-SPC by 36-40%. The hormonally regulated uptake and mobilization of triglyceride suggest active recruitment of surfactant phospholipid substrate by both alveolar connective tissue and epithelial cells.