We investigated the effects of the proportion of arachidonic acid on lymph lipoprotein synthesis in rats, when infused in the presence of lipids with varying degrees of saturation. A single dose of 90 mumol of lipid was administered intraduodenally and intestinal lymph was collected. Emulsion lipid constituents were 90 mumol of [14C]arachidonic acid alone, or either 30 mumol of [14C]arachidonic acid or 5 mumol of [14C]arachidonic acid and 25 mumol of linoleic acid, with 30 mumol of a free fatty acid and 30 mumol of a monoglyceride (the more saturated: oleic acid + monopalmitin; the more unsaturated: linoleic acid + monoolein). Radioactive lymph recovery of [14C]arachidonic acid infused alone reached 32.6 +/- 1.3% of the radioactivity administered and the presence of another fatty acid and a monoglyceride increased it from 38.7 +/- 2.6 to 51.9 +/- 1.1%. For 30 mumol of arachidonic acid, integration into lymph phospholipids was higher when arachidonic acid was infused with oleic acid and monopalmitin than with linoleic acid and monoolein (7.3 +/- 2.7 and 2.8 +/- 0.2% at the absorption peaks, respectively), and it was 4.8 +/- 0.5% when arachidonic acid was infused alone. For 5 mumol of arachidonic acid, the degree of unsaturation of the added lipid did not modify phospholipid incorporation, which was maintained at 6.9 to 7.2%. The proportion and size of chylomicrons increased with the degree of lipid emulsion unsaturation. Percentages of [14C]phospholipids and of chylomicrons were highly correlated. The proportion of arachidonic acid and degree of lipid emulsion unsaturation affected lymphatic arachidonic acid absorption modalities.

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