Determination of the route of medium-chain and long-chain fatty acid absorption by direct measurement in the rat

Background: Medium-chain triglycerides are used for the treatment of malabsorptive states. We measured directly the absorption of medium- and long-chain fatty acids via the mesenteric lymphatics and portal vein in normal animals. These results may be useful in guiding therapy for short- bowel syndrome. Methods: Under anesthesia, male Lewis rats (n = 6) underwent placement of jugular and portal venous lines, mesenteric lymphatic duct cannula, and a duodenal tube. After recovery, a 0.3% lauric acid (C12:0) and 0.37% palmitic acid (C16:0) solution solublized with 3.25 mmol/L lecithin and 23.75 mmol/L taurocholic acid in phosphate-buffered saline was infused at a rate of 3 mL/h via the duodenal tube. After stabilization of lymphatic flow (6 hours), a pulse of radiolabeled lauric and palmitic acid was given via the duodenal tube; absorption was measured by collection of lymphatic fluid and sampling of the portal and jugular venous blood for 4 hours. Results: The amount of acid recovered in the lymphatics was 51% ± 6% (mean ± SD) for lauric and 59% ± 6% for palmitic. For both fatty acids, <1% in total was recovered from the portal vein during the 4-hour postbolus period; thereafter, levels in the blood were constant and very low. At necropsy, the majority of the remaining label was found in the intestine. Conclusions: These results show no evidence for the preferential absorption of medium- chain fatty acids directly via the portal vein in this model. We suggest that further studies be done to measure directly portal vein absorption of the medium-chain fatty acids.