Effect of cold stress on rapeseed oil fed rats

Food safety and health effects of canola oil

Canola oil is a newly marketed vegetable oil for use in salads and for cooking that contains 55% of the monounsaturated fatty acid; oleic acid, 25% linoleic acid and 10% alpha-linolenate [polyunsaturated fatty acid (PUFA)], and only 4% of the saturated fatty acids (SFAs) that have been implicated as factors in hypercholesterolemia. It is expressed from a cultivar of rapeseed that was selectively bred from old varieties in Canada to be very low in erucic acid--a fatty acid suspected to have pathogenic potential in diets high in the original rapeseed oil in experimental animals. Canola oil is free of those problems. It is the most widely consumed food oil in Canada, and has been approved for Generally Recognized as Safe (GRAS) status by the Food and Drug Administration (FDA) of the United States Department of Health and Human Services. The fatty acid composition of canola oil is consistent with its use as a substitute for SFAs, in meeting the dietary goals recommended by many health associations: an average diet containing about 30% of calories as fat made up of less than 10% SFAs, 8-10% PUFAs in a ratio of linoleic to linolenic acids between 4:1 and 10:1, the remainder being monounsaturated fatty acids. No single oil meets these current recommendations for ratios of PUFA/monounsaturated/polyunsaturated fatty acid ratios as the sole source of cooking and salad oil.

Effects of methionine supplementation on the incidence of dietary fat induced myocardial lesions in the rat

Purified diets were prepared to evaluate the effect of methionine supplementation on the incidence and severity of vegetable oil-induced myocardial lesions in the rat. The unsupplemented basal diet fed was similar in nutrient composition to typical semipurified diets currently utilized for cardiopathogenic evaluation of dietary rapeseed oils and contained 1.276 mg of S-amino acid per kilocalorie. The methionine-supplemented diet contained an additional 0.25% (w/w) L-methionine or a total of 1.815 mg of S-amino acid per kilocalorie. Feeding trials were conducted in which weanling rats were fed either a diet containing 20% (w/w) soybean oil (SBO), low erucic acid rapeseed oil (LER) or high urucic acid rapeseed oil (HER) for 16 or 28 weeks. Dietary supplementation with methionine was found to reduce the incidence of focal myocardial lesions in SBO-fed animals to zero. These results suggest that marginal deficiencies in methionine may interact with the frequency and severity of myocardial changes reported for Sprague-Dawley rats fed various dietary oils. The results indicate that levels of essential nutrients should be adjusted when the energy level of the diet is increased.

Effects of cold stress on rats fed different levels of docosenoic acids

Male Sprague-Dawley rats, 4 weeks old, were subjected to an ambient temperature of 4 C for periods up to 24 days and fed a synthetic diet containing one of the following oils: peanut oil (PO), rapeseed oil (RO), low erucic acid rapeseed oil (LO), and partially hydrogenated marine oil (HO), each at 20% w/w. A parallel experiment using the same oils was performed at room temperature (23 C). During cold stress, animals on the RO diet showed higher mortality than all other groups; all 20 animals in this group died within 5 days. At room temperature, however, all animals survived. The lipid accumulation in the heart reached its peak in all groups after 3 days and then gradually declined. The accumulation was most pronounced in the RO animals and coincided with the high mortality at 4 C. The fatty acid composition of the cardiac triglycerides reflected that of the diet, while the composition of the cardiac lecithin was only marginally modified.

Relationship between erucic acid and myocardial changes in male rats

The back and belly fat of pigs fed a diet containing 20% by wt rapeseed oil (22% erucic acid) for 16 weeks was rendered into oil. This rendered pig fat, which contained 5.6% erucic acid, was fed to male rats in three separate experiments at 20% by wt of the diet for 16 weeks. In experiment I rendered pig fat was compared only to Brassica campestris var. Span rapeseed oil containing 4.8% erucic acid. In experiments II and III, rendered pig fat was compared to commercial lard containing 0.2% docosenoic acid, commercial lard to which 5.4% free erucic acid was added, and Span rapeseed oil. There was no significant (P less than 0.01) differences observed in the level of erucic acid in the hearts of rats fed diets of rendered pig fat, Span rapeseed oil, or commercial lard plus erucic acid. However, the incidence (P less than 0.001) and severity (P less than 0.01) of cardiac lesions were significantly higher in Span rapeseed oil fed rats compared to rats fed control diets. The number of rats affected or the severity of lesions in the rendered pig fat fed group was not significantly different from controls. The results of this study indicate that the myocardial lesions associated with feeding 20% rapeseed oil diets are not related to the content of erucic acid per se. The possible reasons why rapeseed oil causes cardiac lesions in rats are discussed. It is suggested that a triglyceride imbalance in the oil might play an important role in causing these lesions in rats.