Triacylglycerol: an important pool of essential fatty acids during early postnatal development in rats.

Developmental changes in the content and composition of major organ lipid pools are not well known. Our objective was to assess quantitatively the changes in lipids, particularly those containing long-chain fatty acids, in the placenta and the brain, liver, and carcass of the fetal and suckling rat. Pregnant dams were killed at days 15, 18, and 21 (term) of pregnancy and the placentas and fetuses removed and analyzed; suckling rats were killed at days +3, +6, and +9 of lactation. Whereas the long-chain fatty acid content of the phospholipids (mg/g) of the fetal or suckling rat remained relatively constant from day 18 of pregnancy to day +9 of lactation, long-chain fatty acids in triacylglycerols increased from prenatal values by 10- to 12-fold during the first 9 postnatal days. Prenatally, triacylglycerol accounted for no more than 32% of total whole body essential fatty acids (day 21), but postnatally this increased to 81-88%. From day 21 to day +9, the proportion of n-6 and n-3 essential fatty acids within the total triacylglycerol pool of the suckling rat increased 71 and 317%, respectively. We conclude that in the suckling rat, triacylglycerol is quantitatively the most important source of essential fatty acids during at least the first 9 days of life.