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 blood flow to the heart. In a rat model of cardiac ischaemia, the susceptibility to develop sustained ventricular fibrillation is increased with the age of the animal, but this increased susceptibility can be diminished by inclusion of polyunsaturated fatty acids (PUFA) in the diet. As the mechanism of action of PUFA probably involves the metabolism of linoleic acid (LA) to arachidonic acid (AA) and thence to the myocardial eicosanoids, an age effect on the conversion of LA to gamma-linolenic 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 LA may be of enhanced benefit in aged animals. We have examined this possibility by feeding either evening primrose oil (9% GLA) or black currant seed oil (17% GLA) to already mature rats for another 48 weeks prior to occlusion of their coronary artery and measurement of the incidence and severity of induced arrhythmias. The results were compared to those from similar age-matched animals fed either saturated animal fat (SF) or sunflower seed oil (SSO) dietary supplements. All PUFA enriched diets were effective with a trend towards diminished arrhythmia with enhanced GLA in the diet. However black current seed oil also contains less LA and more alpha-linolenic acid (ALA; 18:3 n-3) than either sunflower seed oil or evening primrose oil, two circumstances which could lead to enhanced metabolism of dietary n-3 PUFA rather than n-6 PUFA. Previous studies in this laboratory have already demonstrated the effectiveness of the relatively small amount of dietary n-3 PUFA in canola oil in reducing the susceptibility to ischaemic arrhythmia in rats, and this may account for the apparently enhanced benefit of blackcurrant seed oil over evening primrose oil or sunflower seed oil in these experiments.