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.

The fatty-acid composition of rat heart phospholipids was examined after long-term, i.e. more than 12 months, feeding of diets supplemented with n-6 fatty acids as sunflower seed oil (SSO), or n-3 fatty acids as tuna fish oil (TFO) which is a particularly rich source of docosahexenoic acid (DHA). Although some small changes occurred in the relative proportions of palmitic and stearic acids and in the ratio of total saturates to total unsaturates, the most important changes were in the relative proportions of 18:2 n-6 and 20:4 n-6 to 20:5 n-3 and 22:6 n-3. In general, the n-6/n-3 ratio of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and diphosphatidyl glycerol (DPG) was altered in favour of the family of fatty acids administered, although the proportions of the individual long-chain polyunsaturated fatty acids which contributed to this ratio varied from one class of phospholipids to another. In cardiac PC and PE, feeding TFO supplements reduced the proportions of arachidonic acid (AA) and significantly elevated (p less than 0.01) the proportions of DHA but produced relatively little change in those of eicosapentenoic acid (EPA). In DPG, feeding TFO led to a significant increase in the proportion of AA as well as an increase in DHA. The level of EPA was relatively low in PC, PE and DPG even after TFO feeding and never reached comparable levels with that of either AA or DHA. Nevertheless the n-6/n-3 ratio in all these classes of major cardiac phospholipids was significantly reduced by feeding TFO compared to the SSO diet or the commercial rat chow (CC) reference group. In contrast to the reports of other workers who have studied the fatty-acid composition of platelet membranes after feeding various fish oil supplements, in the rat heart the major effect of tuna fish oil is an increase in the proportion of DHA rather than EPA in the cardiac phospholipids.