DIETARY MEDIUM-CHAIN FATTY-ACIDS RAISE AND (N-3) POLYUNSATURATED FATTY-ACIDS LOWER HEPATIC TRIACYLGLYCEROL SYNTHESIS IN RATS

The hypothesis tested was that dietary medium-chain or (n-3) polyunsat urated fatty acids, when compared with (n-6) polyunsaturated fatty aci ds, alter plasma triacylglycerol levels by affecting hepatic triacylgl ycerol synthesis as reflected by the activities of acetyl-CoA carboxyl ase, fatty acid synthase and diacylglycerol acyltransferase in liver. In two separate experiments rats were fed purified diets containing (n -6) polyunsaturated fatty acids in the form of corn oil and either (n- 3) polyunsaturated fatty acids in the form of fish oil or medium-chain triacylglycerols (MCT). Consumption of MCT significantly raised plasm a triacylglycerol concentrations, whereas fish oil feeding had a lower ing effect compared with the corn oil-fed group. In individual rats, t he hepatic triacylglycerol concentration was directly correlated with the plasma triacylglycerol concentration (r = 0.60, P < 0.001). The MC T oil diet vs. the corn oil diet markedly raised the activities of hep atic acetyl-CoA carboxylase, fatty acid synthase and diacylglycerol ac yltransferase. In the rats fed fish oil, the activities of fatty acid synthase and diacylglycerol acyltransferase were significantly reduced , whereas the activity of acetyl-CoA carboxylase was not affected rela tive to activities in rats fed corn oil. The activities of the three e nzymes were directly correlated with plasma triacylglycerol concentrat ions in individual rats (r = 0.60-0.75, P < 0.001). The type of fat in the diet probably affects the rate of hepatic triacylglycerol synthes is which is an important determinant of plasma triacylglycerol concent rations.