Rat LDL metabolism in the perinatal period.

In fetal rats at term LDL carries 75% of the total serum cholesterol, whereas in adult ones this value amounts to 20% only. Using a time-dependent two pool model the flux rates for LDL cholesterol can be calculated for the newborn. The data reveal that at birth the LDL cholesterol flux is 15-20 times higher than in the adult. During the first 2 h of postnatal life the FCR drops down from 0.4 at birth to values measured in the adult. Since at least 75% of LDL is of another origin than VLDL, a direct hepatic LDL synthesis is postulated for the newborn. The liver contributes to about 30% of the total LDL uptake which is mainly realized by a receptor-dependent mechanism, even though the fetus and the newborn exhibit markedly elevated LDL serum concentrations.