A comparison of the metabolism of cis,cis-, cis,trans/trans,cis- and trans,trans-9,12-octadecadienoic acids in rat liver

The effect of geometrical isomers of 9,12-octadecadienoic (18:2) acid on ketogenesis and lipid secretion was compared in isolated perfused rat liver. The hepatic uptake of 18:2 acid isomers was similar in the cis,cis (cc)-, trans,trans (tt)-and a mixture of cis,trans/trans,cis (ct/tc)-isomers. The trans-isomers in comparison with the cis-counterpart stimulated ketogenesis, while reduced hepatic secretion of triacylglycerol and cholesterol and the concentration of triacylglycerol in the post-perfused liver. This reciprocal response was dependent on the number of trans double bonds. The trans-isomers infused during the 4h-perfusion periods were actively incorporated into hepatic lipids and secreted at the expense of endogenous cc-18:2 acid, although the mixture of the mono-trans isomers as compared to the di-trans isomer incorporated more into liver lipids except for phospholipid. On the other hand, less ct-18:2 was incorporated than tc-18:2 into both hepatic and perfusate lipids. These results indicate that both the position and the number of the trans-double bonds in the 18:2 acid determine the pathways of oxidation and esterification.