Long-term adaptation to high-fat diets modifies the nature and output of postprandial intestinal lymph fatty acid in rats.

These studies were designed to investigate the lymph absorption of a lipid emulsion in rats prefed different long-term high-fat diets. Particular emphasis was placed on the consequences of endogenous fatty acid alteration on the lymph recovery of two labeled fatty acids. Male Wistar rats were fed a standard diet (LF) containing 3.5 g/100 g fat or high-fat diets containing 15 g/100 g sunflower oil (HSFO), menhaden oil (HMO) or medium-chain triglyceride oil (HMCT) for 4 wk. The lymph was collected for 3 h before and after the intraduodenal infusion of a 90 micromol lipid emulsion (30 micromol monopalmitin, 30 micromol oleic acid, 25 micromol linoleic acid, 5 micromol arachidonic acid) labeled with [3H] oleic (OA) and [14C] arachidonic (AA) acids. The [3H] OA and [14C] AA lymph recoveries were measured and the lymph samples were tested for fatty acid, phospholipid and triglyceride content. Prefeeding an HSFO or HMO diet led to a 65 or 32% greater total lymph fatty acid output, respectively, compared with rats prefed the LF diet. In rats prefed both the HSFO and HMO diets, lymph fatty acid characteristics provided evidence of a dilution of exogenous fatty acids coming from the emulsion by endogenous fatty acids. In rats prefed the HMCT diet, the total lymph fatty acid output after the infusion of the lipid emulsion was not greater than that of starved rats. Nevertheless, 27% [3H] OA and 21% [14C] AA were recovered in the lymph, suggesting a limited dilution of exogenous fatty acids by endogenous fatty acids. In rats prefed the HMCT diet, some exogenous long-chain fatty acids must have been transported by the portal vein in response to low biliary phopholipid production, as indicated by the proportions of [3H] OA and [14C] AA taken up by the mucosa and not recovered in the lymph. Thus we demonstrated that during absorption of a single long-chain fatty acid meal a dilution of exogenous fatty acids by endogenous fatty acids occurred. The nature and the quantity of these endogenous fatty acids could alter the absorption efficiency of long-chain fatty acids by the lymphatic pathway and modify the fatty acid characteristics of lymph lipoprotein.