Differential utilization of long chain fatty acids during fasting-induced triacylglycerol depletion. III. Comparison of n-3 and n-6 fatty acids in rat plasma and liver.

Previous research has shown that arachidonic acid (20:4(n-6)) is preferentially retained in liver triacylglycerol in fasted compared to fed rats consuming a diet containing n-6 fatty acids. It was hypothesized that eicosapentaenoic (20:5(n-3)) and docosahexaneoic acids (22:6(n-3)) would be similarly retained in liver and plasma triacylglycerol of fasted rats consuming a diet containing n-3 fatty acids. In comparison with fed rats, it was observed that in partially fasted rats consuming diets which contained 5% sunflower oil (78% 18:2(n-6)) or 5% marine fish oil (30% 20:5(n-3) and 22:6(n-3)), both liver and plasma had significantly depleted triacylglycerol levels containing higher proportions of both arachidonic and docosahexaneoic acids but a lower proportion of eicosapentaenoic acid (marine fish oil group only). Separation of liver and plasma triacylglycerol by silicic acid column chromatography and silver nitrate TLC showed that the majority of long chain fatty acids utilized during fasting were derived from the triacylglycerol subclasses containing palmitic acid (16:0), palmitoleic acid (16:1(n-7)) and oleic acid (18:1(n-9)) with retention o both highly saturated and polyunsaturated subclasses. Greater utilization of eicosapentaenoic acid than either arachidonic acid or docosahexaenoic acid during fasting may be due to triacylglycerol speciation of the former with readily oxidized monounsaturated fatty acids.