Altered Levels of n-6/n-3 Fatty Acids in Rat Heart and Storage Fat following Variable Dietary Intake of Linoleic Acid

Abstract

Fat-supplemented diets enriched with linoleic acid by the addition of 12% w/w sunflower seed oil or proportionally reduced in linoleic acid by addition of 12% mutton fat were fed to rats for 18 months before the fatty acid composition of perirenal storage fat and myocardial membranes (phospholipids) was determined. Although the fatty acid composition of perirenal fat generally reflected that of the diet, there was an inverse relationship between the consumption of n-6 and the deposition of n-9 fatty acids. In addition, enhanced deposition of oleic acid (18:l, n-9) appears to be related to the dietary intake of stearic acid (18:0). In contrast, in myocardial membranes the n-3 polyunsaturated fatty acids are found to be increased when the intake of n-6 polyunsaturated fatty acids is reduced. This is particularly evident for docosahexaenoic acid (22:6, n-3) which is significantly increased in phosphatidylcholine, phosphatidylethanolamine, and diphosphatidylgycerol fractions of myocardial membranes, when the mutton fat diet was fed. After feeding the sunflower seed oil diet, the increased consumption of linoleic acid produced only small changes in the 18:2, n-6 content of cardiac phosphatidylcholine and phosphatidylethanolamine. These major classes of membrane phospholipids also showed only small increases in 20:4, n-6. In diphosphatidylglycerol, increased 18:2, n-6 also followed increased dietary intake, but this was not accompanied by increased 20:4, n-6. These changes in myocardial phospholipid fatty acid composition are similar to those observed after short-term feeding reported previously and confirm that changes in dietary n-6/n-3 fatty acid intake affect the fatty acid composition of both myocardial membranes and storage fat. These changes persist for the duration of the feeding period.

Comparative Changes in the Fatty-Acid Composition of Rat Cardiac Phospholipids after Long-Term Feeding of Sunflower Seed Oil- or Tuna Fish Oil-Supplemented Diets

“…Thus, there was no evidence of the retarded growth rate which is indicative of essential fatty-acid deficiency, confirming our earlier observation [ 19] that the levels of 18:2 n-6 provided in these diets are suffi cient to avoid this nutritional deficiency even over the long period of the present study. At sacrifice all animals appeared to be healthy and free of evidence of gross organ pathology.…”

“…Previous studies in this laboratory have demonstrated significant changes in the poly unsaturated fatty-acid profile of the cardiac muscle membranes (phospholipids) of rats after feeding different lipid supplements for either 'short' or 'long'-term periods [17,19]. This general effect was again demonstrated for n-6 and n-3 fatty-acid enriched diets by the results shown in table III, which gives the fatty-acid composition of the total phospho lipids of the left ventricle of the rat heart obtained after 15 months of feeding either an n-6-enriched fatty-acid supplement (the SSO diet) or a diet enriched with n-3 fatty-acids (the TFO diet).…”

“…The fatty-acid composition of the remain ing phospholipids of the cardiac membranes, which is made up of phosphatidylserine, phosphatidylinositol and sphingomyelin [19], could not be determined because of their low levels in the small samples taken for analysis.…”

“…The other two groups received either an n-6 or an n-3 polyunsaturated fatty-acid-supplementcd diet pre pared by refabrication of the standard diet by the addition of 12% (w/w) of oil of either plant or marine origin. Thus, the n-6 unsaturated fatty-acid-rich diet was prepared as described previously [II,19] by refabricating the CC diet with SSO in which 65-70% of the total fatty acids occur as linolcic acid (18:2 n-6), whereas for the n-3-enriched diet, tuna fish oil (TFO) was added in which 30-35% of the total fatty acids occur as EPA (20:5 n-3) or DHA (22:6 n-3) acids. The tuna fish oil was a by-product of a tuna fish pro cessing plant (SAFCOL Seafoods Ltd., Vic.).…”

“…Surprisingly, in spite of these claims, relatively little or no information is available at present on the possible beneficial/deleterious effects of long-term dietary consumption of n-3 fatty acids on either the function or lipid composition of cardiac muscle. This is important as dietary fats, including saturated animal fat and polyun saturated sunflower seed oil (SSO) clearly modify the membrane lipid composition [11,19] of the heart, and alter the suscepti bility to arrhythmia and myocardial infarc tion [12,13].…”