EFFECTS OF FEEDING OYSTER ON LIPID METABOLISM IN RATS
Tsubasa HARAGUCHI, Kazunari TANAKA
Graduate School of Human Health Science, University of Nagasaki, 1-1-1 Manabino, Nagayo-cho, Nishisonogi-gun, Nagasaki, 851-2195, Japan
Key words: dietary oyster, peptide, triglyceride, cholesterol, lipogenesis, fecal excretion
Oyster contains a relatively large amount of glycogen, protein, and minerals such as calcium and zinc. The protein content of lyophilized oyster was approximately 44%. Oyster is also rich in lipid components, EPA, DHA and non-cholesterol sterols. Feeding oyster induced the reduction of serum and liver cholesterol and triglyceride concentrations and the increment of HDL-cholesterol/LDL-cholesterol ratio in SD rats. Also, defatted oyster showed lipid-lowering activity, and the effects were more potent than soybean protein. The excretion of fecal steroids was increased in rats fed oyster and defatted oyster. Therefore, it is thought that components other than lipid fractions are responsible for hypolipidemic actions. Oyster peptides were obtained by hydrolysis of oyster protein with proteases. High molecular oyster peptides (molecular weight: 7,100 ~ 53,400) exerted reduction of serum cholesterol and hepatic triglyceride concentrations in rats.
The activities of hepatic fatty acid synthase and glucose 6-phosphate dehydrogenase, both lipogenic enzymes, were lowered in rats fed oyster peptides. Low molecular peptides which more than 40% of peptides were molecular weight of less than 500 were prepared by some proteases. Feeding low molecular peptides decreased serum and liver triglyceride levels in rats. Low molecular peptide-containing products coating with dextrin also reduced lipid levels. Feeding oyster exerts a potent hypolipidemic actions, and the effect is in partly ascribed to protein and peptide fractions in oyster. It was suggested that the lowering activity is induced through the acceleration of fecal steroid excretion and the suppression of hepatic lipogenesis.