A rapid and specific enzymatic method for the quantification of phosphatidylcholine, disaturated phosphatidylcholine,...

An enzymatic procedure for the quantification of phosphatidylcholine, disaturated phosphatidylcholine, and phosphatidylglycerol in amniotic fluid is described. By use of this method, choline and glycerol are released enzymatically from phosphatidylcholine and phosphatidylglycerol, respectively, in reactions catalyzed by phospholipase D. The hydrogen peroxide generated from choline (by the action of choline oxidase) and from glycerol (by the combined action of glycerokinase and glycerol-3-phosphate oxidase) is quantified spectrophotometrically after the addition of horseradish peroxidase, aminoantipyrine, and phenol. The phosphatidylcholine concentration in amniotic fluid was found to be approximately 10 to 30 nmol/ml between the twenty-third and thirty-sixth week of gestation and increased sevenfold to eightfold between the thirty-seventh week and term. The procedure can be modified for the quantification of disaturated phosphatidylcholine. The concentration of phosphatidylglycerol was approximately 2 nmol/ml between the twenty-third and thirty-sixth week and increased to 10 to 20 nmol/ml between the thirty-seventh and forty-first week of pregnancy. Since contamination of amniotic fluid with bile pigments does not interfere with either assay, the phosphatidylcholine and phosphatidylglycerol concentrations in amniotic fluid can be determined in samples that are contaminated with meconium.