Distribution of the molecular species of phospholipids in human umbilical cord blood.

The composition of phosphatidylcholine (PC) and sphingomyelin (SM) was studied in cord blood lipoproteins to determine whether equilibration of the molecular species of phospholipids among lipoproteins was comparable with that reported for adults. The molecular species distributions of PC in low density lipoprotein (LDL) differed from that of high density lipoprotein (HDL). Whereas LDL PC was richer in combinations of fatty acids with 16 and 18 carbon atoms than HDL, the HDL was markedly enriched in combinations of fatty acids with 18 and 20 carbon atoms. Sphingomyelins in LDL were richer in palmitic acid than HDL while HDL had a greater proportion of long chain sphingomyelin than LDL. The molecular species of PC and SM do not equilibrate in cord blood. The results for the SM distributions were similar to other reports for adult human lipoprotein. However, the marked differential distribution of PC among lipoproteins appears unique to cord blood. The mechanisms responsible for equilibrating PC among lipoproteins are less well developed in the neonate when compared with the adult.