Immaturity alters plasma lipoprotein composition of intravenously alimented newborn infants

Plasma lipoprotein composition in infants receiving fat-free parenteral nutrition reflects the endogenous synthesis and metabolism of lipids. We studied the composition of plasma lipoproteins in 49 appropriate for gestational age newborn infants after surgery who received only glucose and amino acid solutions for 5.4 +/- 0.3 days (M +/- SE). Of the infants studied, 31 were fullterm (gestational age 39.5 +/- 0.2 weeks) and 18 premature (34.3 +/- 0.7 weeks). Plasma lipid levels (total lipids, triglycerides, free cholesterol, sterol, esters, phospholipids) did not differ between term and premature infants, but triglycerides and cholesterol were markedly lower than in young, fasting adults. The contribution of triglycerides to lipoprotein lipids was strikingly low in chylomicrons (21% vs. 90% in young fasting adults) and VLDL (34 vs 60%) and the infants had a consistently lower cholesterol content of HDL (21 mg/dl vs. 45-50 mg/dl in adults) and LDL (43 mg/dl vs. 100 mg/dl). All infantile lipoproteins were enriched with phospholipids. These results are comparable to those reported for cord plasma. In premature babies, VLDL were markedly reduced and contained less triglycerides, free and esterified cholesterol than in term infants. In contrast, HDL were increased in preterm infants and carried more phospholipids. VLDL contributed to al lesser and HDL to a greater extent to plasma lipid transport in premature infants. We conclude that in premature infants hepatic synthesis of triglycerides and cholesterol and their secretion as VLDL is reduced, which may be caused by low substrate availability or an immaturity of the synthetic pathway. In premature infants, HDL appears to play a major role in transporting plasma lipids to peripheral tissues.