Effects of Different Triglyceride Saturated Fatty Acids on Tissue Lipid Level, Fatty Acid Composition, Fecal Steroid Excretion, Prostacyclin Production, and Platelet Aggregation in Rats.

Male Sprague-Dawley rats were fed for 3 weeks cholesterol-enriched diets containing 7% interesterified fats in which saturated fatty acids, lauric, myristic, palmitic, and stearic acids, were the sole variable. The dietary fat was composed of 50% saturated fatty acid, 30% oleic acid, 14% linoleic acid, and 6% α-Iinolenic acid (P/S =0.4, n-6/n-3 =2.3). There was no difference in food intake, body weight gain, or liver and epididymal adipose tissue weight among the groups, although the apparent fatty acid absorption decreased with increasing chain-length of dietary saturated fatty acids. Plasma lipid levels were comparable among the groups, but the concentration of liver cholesterol was significantly lower, and fecal excretion of neutral but not acidic steroids was significantly higher in the stearic acid group even compared with the palmitic acid group. The liver triglyceride decreased upon feeding palmitic or stearic acid fats. The fatty acid composition of adipose tissue but not liver triglyceride apparently reflected the source of dietary fats, but a considerable portion of stearic acid appeared to be desaturated to oleic acid. The proportion of arachidonic acid in plasma cholesterol ester and that of linoleic acid in liver phosphatidylethanolamine decreased with the chain-length of saturated fatty acids. The stearic acid-fat significantly reduced platelet aggegation by ADP and aortic production of prostacyclin, and there was a similar but to a less marked response pattern in the palmitic acid-fat. These observations suggest that the different saturated fatty acids exert differential effects on various lipid parameters.