[Enzymatic colorimetric determination of phosphatidylglycerol in amniotic fluid]

Although the concentration of phosphatidylglycerol (PG) in amniotic fluid is generally considered indicative of fetal lung maturity, the thin layer chromatographic techniques currently used to measure this concentration have been criticized. We have investigated a highly sensitive method for determining amniotic fluid phosphatidylglycerol by using L-glycerol-3-phosphate (G-3-P).dihydroxyacetone phosphate enzymatic cycling reaction and relate this finding to the assessment of fetal lung maturity. Under the assay conditions described above, glycerol oxidase eliminates endogenous glycerol in the amniotic fluid prior to analysis. The subsequent enzymatic reaction sequence involves conversion of phosphatidylglycerol to G-3-P by phospholipase D and glycerol kinase in the presence of ATP. G-3-P is subsequently determined with amplification by enzymatic cycling reaction of G-3-P oxidase and G-3-P dehydrogenase in the presence of oxygen and NADH2. The absorbance is measured at 542 nm. The quantitation of phosphatidylglycerol is linear over the concentration range of 0-20 microM and the detection limit is 0.4 mumol/l. Within run CV's were found to be 1.25% at 13.8 mumol/l (n = 7) and 3.0% at 4.2 mumol/l (n = 7). The results obtained from 48 samples using this procedure, revealed that a level less than 1.0 mumol/l of PG persisted until the 29th week of gestation. A gradual increase in PG (more than 1.0 mumol/1) beginning in the 30th week of gestation was observed. A sharp increase in PG was also found in the 37th week of gestation.