GAMMA-LINOLENIC ACID, BLACK-CURRANT SEED AND EVENING PRIMROSE OIL IN THE PREVENTION OF CARDIAC-ARRHYTHMIA IN AGED RATS

Cardiac Arrhythmia frequently develops as a consequence of reduced blo od flow to the heart. In a rat model of cardiac ischaemia, the suscept ibility to develop sustained ventricular fibrillation is increased wit h the age of the animal, but this increased susceptibility can be dimi nished by inclusion of polyunsaturated fatty acids (PUFA) in the diet. As the mechanism of action of PUFA probably involves the metabolism o f linoleic acid (LA) to arachidonic acid (AA) and thence to the myocar dial eicosanoids, an age effect on the conversion of LA to gamma-linol enic acid (GLA) by Delta 6-desaturase may be involved. If this is so, replacement of LA rich PUFA oils with others containing both GLA and L A may be of enhanced benefit in aged animals. We have examined this po ssibility by feeding either evening primrose oil (9% GLA) or black cur rant seed oil (17% GLA) to already mature rats for another 48 weeks pr ior to occlusion of their coronary artery and measurement of the incid ence and severity of induced arrhythmias. The results were compared to those from similar age-matched animals fed either saturated animal fa t (SF) or sunflower seed oil (SSO) dietary supplements. All PUFA enric hed diets were effective with a trend towards diminished arrhythmia wi th enhanced GLA in the diet. However black current seed oil also conta ins less LA and more alpha-linolenic acid (ALA; 18:3 n-3) than either sunflower seed oil or evening primrose oil, two circumstances which co uld lead to enhanced metabolism of dietary n-3 PUFA rather than n-6 PU FA. Previous studies in this laboratory have already demonstrated the effectiveness of the relatively small amount of dietary n-3 PUFA in ca nola oil in reducing the susceptibility to ischaemic arrhythmia in rat s, and this may account for the apparently enhanced benefit of blackcu rrant seed oil over evening primrose oil or sunflower seed oil in thes e experiments.