Effect of total parenteral nutrition with linoleic acid-rich emulsions on tissue omega 6 and omega 3 fatty acids in the rat.

The effect of total parenteral nutrition (TPN) with lipid emulsions containing ca. 48% 18:2 omega 6 plus 8% 18:3 omega 3 (Intralipid) or 76% 18:2 omega 6 plus 0.5% 18:3 omega 3 (Liposyn) on the fatty acid composition of liver and plasma triglyceride and phospholipid (PL) was studied in the rat. Plasma PL showed a clear influence of the egg PL present in the infused lipid, suggesting replacement of endogenous lipoprotein PL. The incorporation of 20 and 22 carbon omega 6 and omega 3 fatty acids was reduced in liver phosphatidylcholine of rats infused with either Intralipid or Liposyn. Phosphatidylethanolamine was much less affected and showed reduced 20:4 omega 6 and 20:5 omega 3 in the Liposyn group only. Reduction in levels of long chain essential fatty acid metabolites was compensated for by an increased content of saturated fatty acids. There was no accumulation of 18:2 omega 6 or 18:3 omega 3 in liver PL. The similarity between the effects of Intralipid and Liposyn supports the conclusion that 18:2 omega 6, not 18:3 omega 3, was responsible. The data suggest that intravenous administration of high levels of 18:2 omega 6 in parenteral lipid reduces desaturation/elongation of essential fatty acids but does not competitively inhibit esterification of other fatty acids into PL.