CONJUGATED LINOLEIC-ACID (9,11-OCTADECADIENOIC AND 10,12-OCTADECADIENOIC ACID) IS PRODUCED IN CONVENTIONAL BUT NOT GERM-FREE RATS FED LINOLEIC-ACID

Conjugated linoleic acid (CLA) is an anticarcinogen in several model a nimal systems. Conjugated linoleic acid occurs naturally in food and i s present at higher concentrations in products from ruminant animals. Given that certain rumen microorganisms produce CLA from free linoleic acid, we studied the effect of feeding free or esterified linoleic ac id on tissue CLA concentrations using conventional and germfree rats. Conventional rats were fed a 5% (wt/wt) corn oil control diet alone or supplemented with 5% free linoleic acid or 8.63% corn oil (equivalent to 5% linoleic acid in triglyceride). Germ-free rats were fed autocla vable nonpurified diet alone or supplemented with 5% free linoleic aci d. Analyses of CLA concentrations were performed on lipids extracted f rom liver, lung, kidney, skeletal muscle and abdominal adipose tissue, and on liver phospholipid and neutral lipid fractions. Tissue CLA con centrations were higher in conventional rats fed free linoleic acid (t he major isomers were cis-9, trans-11 and trans-9, cis-11) than in con trol animals. Conjugated linoleic acid concentrations in free linoleic acid-fed rats were maximal at 4 wk, and levels were 5-10 times higher than those of controls. Elevated CLA concentrations were also observe d in liver phospholipid and neutral lipid fractions. In contrast, CLA concentrations in the tissues of germ-free rats were not affected by d iet. Feeding the corn oil-fortified diet to conventional rats did not increase CLA concentration in the tissues. We conclude that the intest inal bacterial flora of rats is capable of converting free linoleic ac id (but not linoleic acid esterified in triglycerides) to cis-9, trans -11 and trans-9, cis-11 CLA isomers.