Morphological effects of rapeseed oil in rats. II. Long-term studies.

In long-term studies covering up to 160 days young Sprague-Dawley rats were fed diets containing 40 cal% of fat. The fat component consisted of either conventional rapeseed oil, or Canadian rapeseed oil low in erucic acid, or arachis oil. Myocardial fatty accumulation was demonstrated in light microscopic studies throughout the experiments in rats fed conventional rapeseed oil, but the number of fat droplets decreased with time. The controls fed arachis oil showed no fatty accumulation. In the rats fed conventional rapeseed oil focal myocardial lesions appeared after 40 days on the diet. These consisted of histiocytic infiltration, occurrence of macrophages, myolysis, proliferation of fibroblasts and finally scarring. Such foci were found widely spread in the myocardium of these rats. In the experimental groups given Canadian rapeseed oil from the cultivar Oro no histiocytic foci or scarring were observed. Small myocardial lesions were occasionally found in the control rats. These latter findings were observed on serial sections. It was concluded that this type of lesion is a "normal" finding. The number and size of the foci observed in animals fed conventional rapeseed oil (10% and 2% (w/w) erucic acid in the diet) indicate, however, that they have to be considered pathological under such circumstances. The pathogenesis of the myocardial alteration is discussed and it is concluded that the long-chain fatty acids are responsible. No direct proof has been presented that the described events are of importance in human pathophysiology, However, several circumstances pointing in this direction are discussed. It is concluded that on the basis of our present knowledge a pathological effect of erucic acid and its homologues in man cannot be excluded.