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Time Sequence of Changes in Hepatic Fatty Acid Synthesis in Rats Meal-Fed Polyunsaturated Fatty Acids¹

Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824

Rats were meal-fed once daily methyl esters of palmitate (C_16:0); stearate (C_18:0); linoleate (C_18:2) and linolenate (C_18:8) to determine the influence of these fatty acids on glucokinase and fatty acid synthetase activities and on in vivo rates of fatty acid synthesis in the liver. Addition of 7% C_16:0 or 3% C_18:3 to a fat-free basal diet did not alter the rate at which the diet was removed from the stomach and small intestine. Consumption of a diet containing C_18:2 for eight meals significantly reduced hepatic fatty acid synthetase activity and in vivo rates of fatty acid synthesis by 40%, but did not alter glucokinase activity. At least three meals of a diet containing C_18:2 or C_18:3 were required to inhibit hepatic fatty acid synthesis. Conversely, after rats consumed C_18:2, more than two meals of a fat-free diet were required to increase hepatic rates of fatty acid synthesis. Dietary C_16:0 and C_18:0 did not alter rates of fatty acid synthesis in rat liver. Glucokinase was not influenced by any of the methyl esters fed in all trials except one. The results of this study suggest that polyunsaturated fatty acids can specifically influence hepatic fatty acid synthesis and fatty acid synthetase activity without altering glucokinase activity, and that meal-fed rats must consume at least three meals containing polyunsaturated fatty acids before hepatic fatty acid synthesis or fatty acid synthetase activity is altered.

KEY WORDS: • dietary polyunsaturated fatty acids • fatty acid synthesis • fatty acid synthetase • glucokinase • liver • rat

¹ Supported in part by NIH AM 18957, by NIH GM 01818 and by the Fats and Protein Research Foundation. DRR is the recipient of Career Development Award KO4 AM 00112. SDC was the recipient of an NIH Traineeship. Michigan Agricultural Experiment Station Journal Article No. 7800.

² Current address is Nutrition Program, Johns Hopkins University, School of Hygiene and Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205.

Manuscript received 2 December 1976.