Effects of n-3 polyunsaturated fatty acids on coronary heart disease.

The purpose of this paper is to discuss the role of n-6 and n-3 polyunsaturated fatty acids in coronary heart disease (CHD). The level of n-6 and n-3 fatty acids in plasma and cardiac phospholipids was examined in relation to CHD in man. The fatty acid profile of cardiac phospholipids was also examined in relation to various risk factors of CHD, such as the composition of dietary fat, aging and stress. Life expectancy in Iceland is higher than in other Nordic countries, and the cardiovascular diseases mortality is lower in Iceland in the older age groups. There is a positive correlation between the level of arachidonic acid (AA) in plasma phospholipids (PL) in the normal population and cardiovascular disease mortality in Nordic countries. The level of AA in plasma PL is significantly higher in patients with CHD than in normal subjects. Dietary intake of fish or fish oil lowers cellular levels of AA and favorably influences eicosanoid metabolism in platelets and leukocytes. The roles of n-6 and n-3 fatty acids in heart muscle are less well understood. Rats fed diets containing either 10% butter, corn oil or cod liver oil showed markedly different fatty acid composition of individual phospholipids in sarcolemma. Dietary cod liver oil lowered the AA level in sarcolemmal phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) by 50% compared to butter or corn oil fed rats, replacing AA with docosahexaenoic acid (DHA). Adaptation to moderate to severe stress induced by repeated administration of catecholamines for 15 days resulted in marked but reversible alterations in the fatty acid profile of cardiac phospholipids. During severe stress the level of AA increased by 50% in PC replacing linoleic acid (LA), whereas in PE the DHA increased markedly replacing LA. Aging was accompanied by similar alterations in cardiac phospholipids, increased levels of AA in PC and increased DHA in PE. The incidence of ventricular fibrillation (VF) and sudden cardiac death induced by isoproterenol in adult rats fed different dietary fat was lowest in rats fed cod liver oil, with a low ratio of AA/DHA in cardiac phospholipids. Mortality due to VF was highest in rats fed corn oil with the highest ratio of AA/DHA. Sudden cardiac death in man was frequently associated with a higher ratio of AA/DHA than observed in people of the same age who died in accidents. The balance between n-6 and n-3 fatty acids in cellular phospholipids seems to play an important role in stress tolerance and survival.