Quantitative changes in long-chain fatty acids during fetal and early postnatal development in rats.

The quantitative importance of triacylglycerol as a source of total essential fatty acids during early postnatal development is reported in the accompanying article. Our objective here was to measure the quantitative changes in individual long-chain fatty acids in specific lipid classes of the carcass, liver, and brain of the developing rat mainly to describe the relative accumulation of long-chain vs. precursor fatty acids. Fatty acids in carcass phosphatidylcholine (micrograms/g) were lower at fetal days 18-21 than at either fetal day 15 or postnatal days +3 to +9. Individual long-chain fatty acids in liver phosphatidylcholine and phosphatidylethanolamine increased markedly by day +3 postnatally, whereas in brain phosphatidylethanolamine, the postnatal increase was delayed to between days +6 and +9. Fatty acids in carcass and liver triacylglycerols increased quantitatively by 10- to 300-fold from fetal day 21 to postnatal day +3 with amounts of both arachidonic and docosahexaenoic acid equaling linoleic acid. The ratios of linoleic and alpha-linolenic acids to respective long-chain products were significantly higher in triacylglycerols, whereas that of stearic to oleic acid was higher in phospholipids. We conclude that, during early postnatal life, oleic, linoleic, and alpha-linolenic acids are required in quantitatively greater amounts in triacylglycerols, whereas stearic acid and long-chain essential fatty acids are required in phospholipids.