Effect of extracts from narezushi, a fermented mackerel product, on cholesterol metabolism in Wistar rats

Heshiko extract was separated into peptide and amino acid fractions by ion-exchange column chromatography. Heshiko extract and these fractions were administered to rats in a diet enriched with lipid and cholesterol for 30 days. In the heshiko extract group, increase of triglyceride, total cholesterol, and low-density lipoprotein (LDL)-cholesterol levels in plasma and accumulation of total lipids in the liver were suppressed, while amounts of both lipid and cholesterol excreted to feces were increased. Administration of heshiko extract tended to increase fecal bile acids and promoted the activity of cholesterol 7α-hydroxylase, the rate-limiting enzyme in the synthesis of bile acid from cholesterol in the liver. However, activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol synthesis system in the liver, decreased due to regulation by the feedback of lipid transportation from diet to the liver. The same effect was observed in the peptide and free amino acid fraction groups. These data suggest that both excretion of cholesterol and bile acid to feces and promotion of cholesterol 7α-hydroxylase activity are related to the hypocholesterolemic effects of heshiko extract and that both peptides and amino acids contribute to that effect.