Neonatal umbilical cord blood lipoproteins. Isolation and characterization of intermediate density and low density lipoproteins.

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Abstract
Intermediate density lipoproteins (IDL) (d[density] = 1.006-1.019 g/ml) and low density lipoproteins (LDL) (d = 1.019-1.063 g/ml) were isolated from human umbilical cord blood plasma by sequential ultracentrifugation. The concentration, chemical and apolipoprotein composition, size and size distribution of the neonatal IDL and LDL for both sexes were determined. IDL and LDL from the neonates showed no sex-related differences in composition or concentration. The IDL and LDL were lower in concentration and differed in composition with regard to each other and with regard to the comparable adult fractions. The apolipoprotein (apo) composition showed only the high MW form of apo B present in the IDL, while the LDL showed the presence of 2 lower MW forms of apo B in addition to the high MW form, along with appreciable amounts of apo E and apo A-I. The size distribution of the neonatal IDL and LDL showed a constant pattern, with peaks at .apprx. 300 .ANG. for IDL and 257 and 244 .ANG. for neonatal LDL. The alterations in composition, size and size distribution, and the lower concentrations present in the neonate point to differences between the neonate and the adult in the metabolism of lipoproteins with a density of 1.006-1.063 g/ml.