Effects of Dietary Sea Squirt Viscera on Lipid Metabolism in Rats
Masashi Kawasaki
Department of Science of Living, Morioka Junior College, Iwate Prefectural University
152-52 Sugo, Takizawa, Iwate 020-0693, JAPAN

Sea squirt (Halocynthia roretzi) belongs to Protochordata and can be found mainly around the coast of Japan. In Japan, Halocynthia roretzi is utilized for food. In this study, the effects of dietary sea squirt viscera on serum and liver lipid levels and steroid excretions into feces were investigated in rats.
Rats were fed a basal diet or an experimental diet containing 1, 3, 5 or 10 % of the sea squirt viscera for 3 weeks. The sea squirt viscera were freeze-dried and powdered. The serum total cholesterol concentration was significantly increased at the concentration of more than 3 % of the sea squirt viscera. As for the lipoprotein cholesterol concentrations, the HDL-cholesterol concentration was significantly increased at the concentration of more than 1 % of the sea squirt viscera, whereas the (VLDL+LDL)-cholesterol concentration was not significantly different by the sea squirt viscera. The liver cholesterol and triglyceride contents were significantly decreased at the concentration of more than 3 % and 5 % of the sea squirt viscera, respectively. At the same time, the neutral and acidic steroid excretions into feces were significantly increased by the sea squirt viscera at the concentration of more than 3 % and 5 %, respectively.
Sea squirt contains a high level of taurine as compared with other seafoods. It is well known that taurine increases the fecal excretion of bile acids accompanied by the induction of cholesterol 7α-hydroxylase activity. The conversion of cholesterol into 7α-hydroxycholesterol is the rate-determining step of bile acid biosynthesis and is catalyzed by the enzyme cholesterol 7α-hydroxylase. There is a possibility that taurine might be, at least in part, responsible for the decrease in the liver cholesterol content by the dietary sea squirt viscera in the present study.