Differential effects of geometrical isomers of octadecadienoic acids on ketogenesis and lipid secretion in the livers from rats fed a cholesterol-enriched diet

The effect of cis, cis (cc)- and trans,trans (tt)-9,12-octadecadi- enoic (18:2) acids on ketogenesis and lipid secretion was compared in isolated perfused livers from cholesterol-fed rats. The hepatic uptake of 18:2 acids was comparable in both isomers. The livers perfused with cc-\ 8:2 acid in comparison with those perfused without fatty acid substrate produced approximately 4-fold more ketone bodies accompanying the rise of the (β- hydroxybutyrate:acetoacetate ratio, while the tt-acid isomer further increased these parameters. The hepatic secretion rates of triglyceride and phospholipid as well as cholesterol were all elevated on perfusing the cc-18:2 acid as compared to without fatty acid. In contrast, the rates observed with the cc- 18:2 acid isomer except for phospholipid were intermediate, indicating a reciprocal response in ketogenesis and lipid secretion by the trans isomer. The rate of incorporation of trans- fatty acid into perfusate triglyceride and cholesterol ester were lower than c/s-acid, but vice versa into perfusate phospholipids. On the other hand, the effects of /ra«s-fatty acid on the concentration and composition of hepatic lipids were less clear. These results emphasize the differential effect of geometrical isomers of the 18:2 acids on oxidation and esterifica- tion even in the livers containing a high level of cholesterol.