Effect of dietary lipid composition on rat liver microsomal phosphatidylcholine synthesis.

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 omega 3 fatty acid levels and altered the ratio of omega 6 to omega 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 omega 6 fatty acids to omega 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.