Fatty Acid Components of Rat Liver Lipids: Effect of Composition of the Diet and of Restricted Access to Food

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Abstract
The compositions of the fatty acid moieties of the principal liver lipid fractions were determined for groups of young rats fed ad libitum and with access to food for only two one-hour periods daily. Plasma lipid data for the same rats were reported previously. Diets were semisynthetic, and differed only in respect to fat and cholesterol content. One contained 10% of cottonseed oil, the other, 10% of coconut oil. Each fat was fed with and without 1% of cholesterol. Animals were supplied with the diet at weaning and sacrificed 7 weeks thereafter. Variations in the proportions of the fatty acids of the principal liver lipid fractions with diet and method of feeding are reported. It was evident that linoleic acid must be selectively retained in liver. Linoleic acid percentages in the liver cholesterol ester of coconut oil-fed animals were higher than in coconut oil itself even when time of access to food was limited and cholesterol was fed. The percentages of arachidonic acid in liver cholesterol ester were much lower than in plasma ester, particularly so in animals with restricted access to cholesterol-rich diets. On the other hand, the percentage of arachidonic acid of the mono- and diglyceride and free fatty acid fraction was maintained between 6 and 10% in the livers—and was too small to measure in plasma. Lauric and myristic acids, which constitute over 60% of the fatty acids in coconut oil, were present only in small amounts either in liver or plasma. Although percentages of monoenoic acids in liver lipids were increased when the polyunsaturated acids were decreased, percentages of saturated acids of some of the lipid fractions were decreased at the same time. Variations in the fatty acid components of the liver lipids with the stresses imposed by dietary fat, by restricted access to food, and by addition of cholesterol to the diet, suggest that there is a tendency toward maintenance of physical properties of each lipid within a characteristic range, rather than maintenance of a relatively constant ratio of saturated to unsaturated acid such as that found in the plasma lipids. Composition of the phospholipids was more nearly independent of diet and method of feeding than was that of the other lipids. The latter was true for both liver and plasma.