Total hydrolyzable glycerol in amniotic fluid, and its relationship to fetal lung maturity

We describe an enzymic quantification of total hydrolyzable glycerol in amniotic fluid. An extract of amniotic fluid is hydrolyzed in mild alkali, without pretreatment with lipase. The resulting glycerol (some of which may be derived from trace amounts of triglyceride) is then enzymatically phosphorylated with adenosine 5'-[gamma 32P]triphosphate to yield glycerol [gamma 32P]phosphate. After removal of excess [gamma 32P]ATP by charcoal, the radioactivity of the glycerophosphate is measured in a liquid scintillation counter. The close correlation (r = 0.96) we found between total hydrolyzable glycerol and phosphatidylglycerol indicates that the contribution of triglyceride to the value for total glycerol is inconsequential. This method is less time consuming and more precise than the method for phosphatidylglycerol.