Intestinal lymph lipid fatty acid origin and characteristics in fasting rats prefed with sunflower, menhaden or medium chain triglyceride high fat diets

A study was undertaken to compare the influence of different high fat diets on fatty acid composition and output of bile and lymph lipids in fasting rats. Moreover, the lipid fatty acid composition and concentration of adipose tissue and liver on the one hand and plasma on the other hand were determined. Male Wistar rats were fed a normolipidic diet (NL) or hyperlipidic diets containing 15% sunflower oil (HSFO), 15% menhaden oil (HMO) or 15% medium chain triglyceride (HMCT) for 4 weeks. The appearance of the characteristic fatty acids of the diets or of those resulting of their hepatic metabolism at the different levels of the organism was emphasized. Indeed the HSFO diet led to an increased fatty acid concentration in adipose tissue, the lipemia was increased by HMCT diet and decreased by HMO diet. An original result was the significant decreases in bile flow and fatty acid output observed with the HSFO diet when compared to the NL diet. Biliary fatty acid outputs were subjected to variations which did not lead, in all groups, to concommitant modifications of lymph lipid fatty acid outputs. Particularly, after a HMCT diet, the total biliary fatty acid output was significantly reduced and was roughly one quarter of the lymph fatty acid output while it was roughly half after a NL, HSFO or HMO feeding. So the contribution of plasma fatty acids to the constitution of lymph lipoproteins was thought to be more important in the HMCT prefed rat group. For example, fatty acids like 16:0, 18:0, or 20:4n-6 were undoubtly provided by the plasma according to their low biliary concentrations and their relative high proportions in the lymph. These data showed the central role of the liver in determining the fatty acid composition of plasma and bile and consequently of intestinal lymph in the fasting rat and probably in the postprandial state.