Regulation of polyunsaturated fatty acid metabolism in tissue phospholipids of obese (fa/fa) and lean (fa/−) Zucker rats. 1. Effect of dietary lipids on cardiac tissue

The present investigation addressed three questions: (i) Does the obese syndrome alter the fatty acid composition of cardiac tissue and membrane phospholipids in obese (fa/fa) rats? (ii) Are changes, if they occur, similar to those reported for tissues of the genetically obese (ob/ob) mouse? (iii) Can cardiac tissue phospholipids and their component fatty acids be modified by dietary lipids and if so does this occur to the same extent in both fa/fa and lean (Fa/−) rats? Proportions of polyunsaturated fatty acids (PUFA) in cardiac total phospholipids of fa/fa rats differed significantly from those of Fa/− rats and from those reported for ob/ob mice. Increased 18∶2n−6 and decreased 20∶4n−6 and 22∶6n−3 in fa/fa rats indicated impaired PUFA metabolism, possibly reduced Δ6 and/or Δ5 desaturase activity, compared with Fa/− rats. No differences in hepatic Δ6 and Δ5 desaturase activity between fa/fa and Fa/− were found but enhanced activity of Δ9 desaturase activity in fa/fa as compared to Fa/− was evident. Inclusion of sunflower oil (SO) or triolein (TO) at 5% and 20% by weight in the diet elicited marked changes in the fatty acyl composition of cardiac phospholipids in both fa/fa and Fa/− rats when compared with animals fed the control Oxoid diet alone. Supplementation with triolein was most effective, reducing 18∶2n−6 and increasing 20∶4n−6 proportions in fa/fa rats so that they resembled those in Fa/− rats fed the control Oxoid diet. The type of fat rather than the amount of its dietary intake appears to be the main determinant of the observed changes in phospholipid composition. Pair feeding hyperphagic fa/fa rats to the lower intakes of Fa/− rats did not abolish the characteristic differences in the proportions of PUFA in cardiac phospholipids between the two phenotypes. The effect of triolein on cardiac phospholipid fatty acid composition in the present studies is intriguing and may be relevant in understanding the beneficial role of dietary olive oil in ameliorating cardiovascular disease in man.