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Effect of Dietary Lipid Composition on Rat Liver Microsomal Phosphatidylcholine Synthesis¹

Nutrition and Metabolism Research Group, Departments of Foods & Nutrition and Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2C2

Effects of dietary lipid on microsomal membrane fatty acid composition and phosphatidylcholine synthesis were examined with respect to the degree of saturation and chain length of dietary fatty acids. Diets containing 20% fat (wt/wt), primarily in the form of coconut oil, beef tallow, or soybean oil were fed to weanling rats for 28 d. All diets were adequate in essential fatty acids. Feeding the coconut oil diet, containing more than 50% saturated medium-chain fatty acids, increased the long-chain 3 fatty acid levels and altered the ratio of 6 to 3 fatty acids in membrane phosphatidylcholine and phosphatidylethanolamine compared to that in animals fed diets containing a saturated tallow or polyunsaturated soybean oil diet. Change in membrane fatty acid composition in response to the coconut oil diet was accompanied by decreased synthesis of phosphatidylcholine via the cytidine diphosphate choline (CDP-choline) pathway, and increased synthesis via the phosphatidylethanolamine methyltransferase (PEMT) pathway. An overall decrease in phosphatidylcholine production was reflected in a lower ratio of phosphatidylcholine to phosphatidylethanolamine in the membrane. Modulation of hepatic phosphatidylcholine synthesis during early growth thus appears to be in response to the ratio of long-chain 6 fatty acids to 3 fatty acids in membrane phospholipid rather than levels of specific fatty acids or the relative degree of saturation of fatty acids in the diet.

KEY WORDS: • rat • microsomal membrane • phospholipid synthesis • dietary fat

¹ Supported by the Natural Sciences and Engineering Research Council of Canada. D. Pehowich was supported by an Alberta Heritage Foundation for Medical Research Postdoctoral Fellowship. K. M. Hargreaves was supported by a Studentship from the Alberta Heritage Foundation for Medical Research. M. T. Clandinin is a Scholar of the Alberta Heritage Foundation for Medical Research.

² Dr. K. M. Hargreaves, Neurosurgical Research Unit, LaSalle Building, Queen's University, Kingston, Ontario K7L 3N6.

³ Address reprint requests to: Dr. M. T. Clandinin, Department of Foods & Nutrition, 318f Home Economics Building, University of Alberta, Edmonton, Alberta, CANADA, T6G 2M8.

Manuscript received 10 March 1988. Revision accepted 14 November 1988.

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