Tissue phospholipids during human pregnancy by 31P NMR: myometrium, decidua, placenta and fetal membranes.

The biophysical environment formed by phospholipids, rather than the amount of functional proteins, can be rate limiting for factors controlling myometrial contractility and pregnancy maintenance. We therefore studied myometrial, decidual, placental and fetal membrane phospholipids using the 31P NMR spectrum. This enabled us to identify bulk phospholipids over 0.05 mmol/kg. The method was checked for reliability for the reproductive tissues studied. The chemical shift of phospholipid standards was slightly different according to whether a single compound or a mixture was analyzed. The bulk phospholipids found were phosphatidylcholine (PC), phosphatidylethanolamine, sphingomyelin (SM) and phosphatidylinositol. The ratio PC/SM decreased during pregnancy in the decidua, placenta and fetal membranes, but not in the myometrium. Pregnancy did not induce significant changes in the total myometrial phospholipids. Their composition was stable even during clinical labor. The fetal tissues, placenta and fetal membranes contained about twice as much phospholipid as the maternal tissues, myometrium and decidua. There was no sign of lysocompounds, cardiolipin or phosphatidic acid. This supports the view that the extraction and analyzing techniques used earlier probably created artefacts. The increased fluidity of the myometrial and placental phospholipids during pregnancy may depend on factors other than the composition of phospholipids.