Male Sprague-Dawley rats were fed for one week diets containing 20% by weight fat/oil mixtures with different levels of
erucic acid (22:1n-9) (approximately 2.5 or 9%) and total
saturated fatty acids (approximately 8 or 35%).
Corn oil and high
erucic acid rapeseed (HEAR) oil were fed as controls. The same hearts were evaluated histologically using
oil red O staining and chemically for cardiac
triacylglycerol (TAG) and 22:1n-9 content in cardiac TAG to compare the three methods for assessing
lipid accumulation in rat hearts. Rats fed
corn oil showed trace myocardial
lipidosis by staining, and a cardiac TAG content of 3.6 mg/g wet weight in the absence of dietary 22:1n-9. An increase in dietary 22:1n-9 resulted in significantly increased myocardial
lipidosis as assessed histologically and by an accumulation of 22:1n-9 in heart
lipids; there was no increase in cardiac TAG except when HEAR oil was fed. An increase in
saturated fatty acids showed no changes in myocardial
lipid content assessed histologically, the content of cardiac TAG or the 22:1n-9 content of TAG at either 2.5 or 9% dietary 22:1n-9. The histological staining method was more significantly correlated to 22:1n-9 in cardiac TAG (r = 0.49; P less than 0.001) than to total cardiac TAG (r = 0.40; P less than 0.05). The 22:1n-9 content was highest in cardiac TAG and
free fatty acids. Among the cardiac
phospholipids, the highest incorporation was observed into
phosphatidylserine, followed by
sphingomyelin. With the addition of saturated fat, the
fatty acid composition showed decreased accumulation of 22:1n-9 and increased levels of arachidonic and
docosahexaenoic acids in most cardiac
phospholipids, despite decreased dietary concentrations of their precursor
fatty acids, linoleic and
linolenic acids.