Human amniotic fluid contains fibroblast-pneumonocyte factor

We have studied 41 samples of human amniotic fluid collected at 27-40 wk gestation. After 'stripping' with Florisil, most fluids studied stimulated [3H] choline incorporation into saturated phosphatidylcholine by human fetal alveolar Type II cells. The activity declined with advancing gestation and was inversely related to cell number following incubation. Following acid-ethanol extraction, activity eluted from Sephadex G75 columns in 1 M acetic acid with a Kd of approximately equal to 0.4-0.6, and was greater at earlier gestations (27-31 wk) than at later periods (32-36 or 37-40 wk). In contrast, chromatography at neutral pH without prior extraction resulted in retarded elution. The active material was shown to be heat-stable. Thus, the biochemical features of activity recovered from human amniotic fluid are identical to fibroblast-pneumonocyte factor recovered from supernatant culture media of cortisol-treated human fetal lung fibroblasts.