LONG-TERM ADAPTATION TO HIGH-FAT DIETS MODIFIES THE NATURE AND OUTPUTOF POSTPRANDIAL INTESTINAL LYMPH FATTY-ACID IN RATS

These studies were designed to investigate the lymph absorption of a l ipid emulsion in rats prefed different long-term high-fat diets. Parti cular emphasis was placed on the consequences of endogenous fatty acid alteration on the lymph recovery of two labeled fatty acids. Male Wis tar rats were fed a standard diet (LF) containing 3.5 g/100 g fat or h igh-fat diets containing 15 g/100 g sunflower oil (HSFO), menhaden oil (HSFO) or medium-chain triglyceride oil (HMCT) for 4 wk. The lymph wa s collected for 3 h before and after the intraduodenal infusion of a 9 0 mu mol lipid emulsion (30 mu mol monopalmitin, 30 mu mol oleic acid, 25 mu mol linoleic acid, 5 mu mol arachidonic acid) labeled with [H-3 ] oleic (OA) and [C-14] arachidonic (AA) acids. This [H-3] OA and [C-1 4] 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 out put, respectively, compared with rats prefed the LF diet. In rats pref ed both the HSFO and HMO diets, lymph fatty acid characteristics provi ded evidence of a dilution of exogenous fatty acids coming from the em ulsion by endogenous fatty acids. In rats prefed the HMCT diet, the to tal lymph fatty acid output after the infusion of the lipid emulsion w as not greater than that of starved rats. Nevertheless, 27% [H-3] OA a nd 21% [C-14] AA were recovered in the lymph, suggesting a limited dil ution of exogenous fatty acids by endogenous fatty acids. In rats pref ed 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 [H-3] OA and [C-14] AA taken up by the mucosa and not recovered in the lymph. Thus we demons trated that during absorption of a single long-chair. 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 al ter the absorption efficiency of long-chain fatty acids by the lymphat ic pathway and modify the fatty acid characteristics of lymph lipoprot ein.