COMPARISON OF THE EFFECTS OF DIETARY FISH OILS WITH DIFFERENT N-3 POLYUNSATURATED FATTY-ACID COMPOSITIONS ON PLASMA AND LIVER LIPIDS IN RATS

The effects of dietary fish oils with different n-3 polyunsaturated fatty acid compositions on plasma lipid profiles in rats have been studied. Forty-eight male rats, previously maintained on a cholesterol-free diet for 15 days, were fed for 60 days with diets supplemented with 10% fat of either marine hilsa fish (Hilsa ilisa, family clupeidae) or fresh-water chital fish (Notopterus chitala, family notopteridae). The diets had similar levels, of total saturated (35-41%), monounsaturated (43-47%) and n-3 polyunsaturated (9-10%) fatty acids. Cholesterol contents of the diets were adjusted to 0.85%; gamma-linolenic acid (3.3%) in chital oil and eicosapentaenoic acid (4.9%) in hilsa oil diets were the major n-3 contributors. The percentage of eicosapentaenoic acid in the chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic (EPA) to arachidonic acid (AA) ratio in the latter (4.08) was 3.2 times that of the former (1.27). Sixty days of hilsa oil diet feeding decreased the levels of cholesterol (53.3 +/- 2.9 to 50.0 +/- 1.1 mg/dL), triacylglycerol (75.7 +/- 3.8 to 64.3 +/-2.6 mg/dL) and phospholipid (55.8 +/- 1.5 to 51.7 +/- 3.1 mg/dL) in rat plasma. Similar treatment with chital oil diet elevated the plasma cholesterol level (53.3 +/- 2.9 to 62.3 +/-7.6 mg/dL) while triacylglycerol and phospholipid contents remained unaltered. Both the dietary treatments decreased the levels of linoleic and arachidonic acids in liver but only under the hilsa oil diet did the eicosapentaenoic acid percentage increase markedly (0.8 +/- 0.06% to 5.5 +/-0.06%) at the expense of arachidonic acid. This study strongly suggests that the hypolipidemic effect depends on the composition of the n-3 polyunsaturated fatty acids rather than on the total n-3 polyunsaturated fatty acid content of the dietary fish oil.