Effects of dietary alpha- or gamma-linolenic acid on levels and fatty acid compositions of serum and hepatic lipids, and activity and mRNA abundance of 3-hydroxy-3-methylglutaryl CoA reductase in rats.

The effects of diets containing equal amounts of alpha (alpha)- or gamma (gamma)-linolenic acid on lipid metabolism were compared in rats. Four groups of male Wistar rats were given the diets containing 20% perilla/corn mixed oil or borage oil in the absence (PO- and BO-diets, respectively) or presence (CPO- and CBO-diets) of cholesterol for 20 days. The PO-diet yielded lower serum cholesterol than the BO-diet, although the difference was not observed between the CPO and CBO groups. The PO and CPO groups showed lower high-density lipoprotein cholesterol than the BO and CBO groups, respectively. A similar tendency was observed in serum phospholipids. The CPO-diet gave markedly lower hepatic triglycerides than the CBO-diet. The activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was much lower on the PO-diet than on the BO-diet. mRNA abundance of HMG-CoA reductase was lower in rats on the PO-diet than on the BO-diet, though there was no significant difference between the CPO and CBO groups. The present results indicate that alpha-linolenic acid exhibits a larger hypocholesterolemic effect than gamma-linolenic acid, and it may be displayed mainly through the repression of the activity and mRNA expression of HMG-CoA reductase.