LIPOGENIC ENZYME GENE-EXPRESSION IS QUICKLY SUPPRESSED IN RATS BY A SMALL AMOUNT OF EXOGENOUS POLYUNSATURATED FATTY-ACIDS

An examination was conducted of the time courses of incorporation of p olyunsaturated far, acids (PUFA) into lipids of plasma, liver and its nuclei, and the time courses of hepatic lipogenic enzyme gene expressi on after oral administration of perilla oil by a stomach tube to rats fed a fat-free diet. Linolenic acid, 18:3(n-3), and eicosapentaenoic a cid, 20:5(n-3), were considered indices of exogenous fatty acids. in t otal lipids of liver and its nuclei, linolenic acid was detected 1 h a fter the intubation, continued to increase during the first 4 h, then decreased and almost disappeared by 48 h. Eicosapentaenoic acid also i ncreased within only 1 h of intubation, reached a maximum after 8 h an d then gradually decreased. In contrast with the increase of exogenous PUFA, the mRNA concentrations of hepatic lipogenic enzymes began to d ecrease 2 h after the perilla oil intubation, were at a minimum at 8 h , and then increased. In another experiment to examine the effects of dietary perilla oil concentration on PUFA incorporation and gene expre ssion, rats were given diets containing 0-10% perilla oil (supplemente d with hydrogenated fat to 10% fat) for 3 d. Only 1% perilla oil eleva ted the exogenous PUFA concentrations in liver and its nuclei in compa rison with concentrations in rats fed a hydrogenated fat diet. Perilla oil at 2% of the diet was sufficient to suppress lipogenic enzyme gen e expressions, which were suppressed to the minimum level by 5% perill a oil in the diet. Thus, lipogenic enzyme gene expression was quickly suppressed by a small amount of exogenous PUFA, in contrast with the i ncrease of PUFA incorporation into liver and its nuclei. Newly incorpo rated exogenous PUFA appear to be involved in suppression of lipogenic enzyme gene expression.