EARLY POSTNATAL-DEVELOPMENT IN THE RAT IS CHARACTERIZED BY ACCUMULATION OF HIGHLY UNSATURATED TRIACYLGLYCEROLS

Our objective was to determine the quantitative changes of individual triacylglyercol (TG) species in liver and carcass during early postnatal growth. Pregnant rats were killed at d 21 of pregnancy, and neonatal rats were killed at d 3 or 9 after birth. Quantitative changes in fatty acids and TG species of fetal/neonatal liver and carcass were determined using capillary gas liquid chromatography. At postnatal d 3 or 9 compared with fetal d 21, total carcass TG increased 11- to 12-fold, with nonessential fatty acids increasing 8- to 9-fold, n-6 essential fatty acids (EFA) increasing 34- to 44-fold, and n-3 EFA increasing 19- to 29-fold, respectively. Total neonatal liver TG increased 13-fold from fetal d 21 to postnatal d 3, with a 6-fold increase in non-EFA, a 34-fold increase in total n-6 EFA and a 65-fold increase in total n-3 EFA. At postnatal d 3 compared with fetal d 21, larger molecular weight liver TG classes (C56-C64) increased 68-fold, followed by lower molecular weight TG classes C40-C48 (19-fold) with only a 6-fold increase in C50-C54. In liver, highly unsaturated TG classes (C56-C64) accounted for 49% of total TG at postnatal d 3 and consisted mainly of arachidonic, docosahexaenoic, and linoleic acids accompanied by palmitic and oleic acids. During early postnatal development, TG species containing one, two, or even three 20-22 EFA may be structurally important themselves or serve as direct substrates for synthesis of phospholipids. The unique accumulation of C54-C64 TG species, especially in liver, indicates that highly unsaturated TG are a quantitatively important EFA pool during early life.