Lipoproteins and apoproteins of fetal and newborn piglets.

Serum lipids, very low in the fetus and at birth, increased rapidly after the first feeding. Cholesterol was mainly in the free form. Esterified cholesterol rose rapidly, but free cholesterol remained in high proportions (30%) until after weaning. Very high phospholipid concentrations show that triglycerides are not the only major product of esterification and suggest a possible use for energetic purposes. Fetal lipoproteins had a general pattern similar to that of adults, but high-density lipoproteins (HDL) were denser (1.128 g/ml) and correspondingly richer in proteins. The presence of apoprotein AI and of the light intestinal form of apoprotein B in the triglyceride-rich fractions as well as that of apoprotein AIV in HDL was indicative of an early contribution of enterocytes to the lipoprotein pool. Low-density lipoprotein apoproteins were heterogeneous until 14 days, as they are in the human fetus, and contained, besides apoprotein B, all the main apoproteins, HDL reached concentrations of 400 mg/100 ml at 3 and 4 weeks of age, above 3-fold higher than those of chow-fed adults, but also 1.5-fold higher than those of growing pigs fed a 20% fat diet, thereby showing a high capacity of the very young animal to synthesize HDL and apoprotein AI in particular. The many similarities with the evolution of lipoprotein in the newborn human validate the young pig as a model in the study of perinatal nutrition.