EFFECTS OF DIETARY ALPHA-LINOLENIC, EICOSAPENTAENOIC AND DOCOSAHEXAENOIC ACIDS ON HEPATIC LIPOGENESIS AND BETA-OXIDATION IN RATS

The effects of dietary alpha-linolenic, eicosapentaenoic and docosahex aenoic acids on the enzyme activities related to hepatic lipogenesis a nd P-oxidation were compared under constant polyunsaturated/monounsatu rated/saturated fatty acids and n-6/n-3 ratios of dietary fats in rats . Dietary fat containing linoleic acid as the sole polyunsaturated fat ty acid (PUFA) was also given as a control. The concentration of serum triglyceride and phospholipid in the three n-3 PUFA groups was lower than in the linoleic acid group. The hepatic triglyceride concentratio n was lower and the phospholipid concentration was higher in the three n-3 PUFA groups than in the linoleic acid group. Cytosolic fatty acid synthase (FAS) activity was lower in the n-3 PUFA groups than in the linoleic acid group, the reduction being more predominant in the eicos apentaenoic acid and docosahexaenoic acid groups than in the alpha-lin olenic acid group. The cytosolic activities of the NADPH-generating en zymes, glucose-6-phosphate dehydrogenase (G6PDH) and the malic enzyme, were lower in the three n-3 PUFA groups. The activity of carnitine pa lmitoyltransferase (CPT) in mitochondria was higher only in the eicosa pentaenoic acid group than in the other groups. The activity of Mg2+-d ependent phosphatidate phosphohydrolase (PAP) in microsomes and cytoso l was lower in the eicosapentaenoic and docosahexaenoic acid groups th an in the linoleic acid group, while there was no effect of dietary fa ts on the activities of diacylglycerol acyltransferase (DGAT) and glyc erol-3-phosphate acyltransferase (G3PAT) in microsomes. The CTP: phosp hocholine cytidylyltransferase (CT) activity in the homogenate was low er in the n-3 PUFA groups, the reduction being more prominent in the e icosapentaenoic and docosahexaenoic acid groups than in the alpha-lino lenic acid group. The choline kinase (CK) activity in cytosol was lowe r in the eicosapentaenoic acid group than in the linoleic acid group. These results showed that dietary alpha-linolenic, eicosapentaenoic an d docosahexaenoic acids differently influenced hepatic lipogenesis and the partition of fatty acid into oxidation or glycerolipid synthesis.