The role of sera, growth factors, and hormones in the in vitro production of disaturated phosphatidylcholine and propagation of undifferentiated type II alveolar cells from the fetal rabbit lung.

Undifferentiated type II alveolar cells isolated from the fetal rabbit lung were cultured in chemically-defined medium supplemented with 10% carbon-stripped fetal bovine serum for 2-3 days and then placed in serum-free medium, or medium supplemented with either 10% carbon-stripped fetal bovine serum (sFBS) or 10% unstripped fetal bovine serum. Cells exposed to the latter treatment showed the highest growth rate but the lowest level of [3H]choline incorporation into disaturated phosphatidylcholine (DSPC). Cells in serum-free medium showed the lowest rate of growth but removal of serum components stimulated a rapid increase in radioactive precursor incorporation. Cells exposed to the stripped serum were intermediate in both measurements. Incubation of undifferentiated type II cells with EGF stimulated growth but only in the presence of sFBS. EGF also stimulated [3H]choline into DSPC after 48 hours of exposure to the peptide. This latter response could only be elicited in serum-free medium. In the presence of sFBS no effect of the peptide was detected on radioactive precursor incorporation. Similarly dexamethasone (0.55 nM) or 20% medium which had been conditioned by fetal lung fibroblast monolayers did not stimulate [3H]choline in DSPC in the presence of sFBS. In contrast these agents did evoke a significant increase in radioactive precursor incorporation when the undifferentiated type II alveolar cells were incubated in serum-free medium.