Fetal lamb amniotic fluid: Relationship of lipid composition to surface tension

Abstract

The amniotic fluid from 22 lambs delivered near term was used for surface tensionstudies and analysis of the major lipid fractions. Amniotic fluid did not possess “low” surface tension values as did fetal tracheal fluid and lung extracts. The total lipid composition was one fifth to one tenth that found in fetal tracheal fluid, and there was a higher proportion of neutral lipids to phospholipids. The major phospholipids contained in the amniotic fluid were: lecithin, sphingomyelin, and phosphatidylethanolamine, present in amounts less than one fifteenth that in tracheal fluid. The phospholipid fraction isolated from the amniotic fluid possessed “low” surface tension and had a hysteresis loop similar to that of tracheal fluid. These results suggest that the high surface tension of amniotic fluid may be due to quantities of active phospholipids at the air-liquid interface insufficient to form a monomolecular film. The studies also suggest that inspiration of amniotic fluid into the fetal lung would be disadvantageous for normal respiration.