Partitioning of polar fatty acids into lymph and portal vein after intestinal absorption in the rat.

We tested the hypothesis that fatty acids destined for the portal vein after intestinal absorption would be diverted into lymph when infused along with a saturated long-chain fatty acid. Thoracic fistula rats were infused intraduodenally with either linolenic (18:3), lauric (12:0), or decanoic (10:0) acid, or with each fatty acid in combination with 5 mM palmitic acid (16:0), in micellar solutions of taurocholate (10 mM) and 2-mono-oleoylglycerol. Lymphatic transport of linolenic acid was enhanced by co-absorption with palmitic acid: when 0.1 mM linolenic acid was infused alone, 32 +/- 8% of that absorbed and transported beyond the mesentery was carried in lymph. The addition of palmitic acid to the infusate increased the percentage transported in lymph to 56 +/- 10% (P less than 0.005). The increment was due to enhanced intracellular re-esterification of linolenate into triacylglycerol. When 5 mM linolenic acid was infused, the comparable figures for lymphatic transport were 55 +/- 2% for linolenate infused alone and 66 +/- 6% for linolenate infused with palmitate (P less than 0.005). In contrast, the predominantly portal venous transport of lauric and decanoic acids was unaffected by co-absorption with palmitate. We conclude that the partitioning of long-chain fatty acids between portal blood and lymph is dependent on the luminal milieu, in addition to polarity of the fatty acid and the rate of absorption. Unsaturated long-chain fatty acids have a substantial portal transport under conditions which simulate normal food ingestion.