Lymphatic delivery and in vitro pancreatic lipase hydrolysis of glycerol esters of conjugated linoleic acids in rats

We examined the intestinal delivery of conjugated linoleic acids (CLA) given in their triacylglycerol form in the mesenteric lymph of rats. Emulsions containing a mixture of the trilinolein/triester of CLA (9:1) and a tri-[1-(14)C]-linoleyl-sn-glycerol tracer were administered by force-feeding. Lymph was collected over two time periods (0-6 and 6-24 h), and the apparent recovery of CLA was determined relative to that of [1-(14)C]-18:2(n-6). A mixture of CLA-triester/trilinolein (1:9), trilinolein or CLA-triester was separately subjected to pancreatic lipase hydrolysis in vitro to determine whether the lymphatic recovery of CLA was correlated with the initial step of digestion. Lymphatic recovery of CLA was similar to that of 18:2(n-6) (95.6+/-9.0% of the linoleic acid recovery), and isomer repartition was similar in lymph and in the oil fed, indicating that all the CLA isomers were equally absorbed by the enterocytes. Unexpectedly, the in vitro release of CLA into the absorbable forms (free fatty acids and 2-monoacyl-sn-glycerol) was consistently lower than that of 18:2(n-6). Moreover, the 9c, 11t-isomer of CLA was also released faster into the absorbable forms than its 10t,12c homolog (P = 0.05). We cannot ascribe a distinct cellular accumulation or a difference in the biological effects of different CLA isomers on the ground of a selective intestinal absorbability. Also, the physiological conditions prevailing in vivo in the digestive tract are likely to overcome the relative resistance of CLA ester bonds to pancreatic lipase hydrolysis and allow a lymphatic recovery of CLA similar to that of linoleic acid.