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Effects of Excess Dietary Tyrosine on Cholesterol, Bile Acid Metabolism and Mixed-Function Oxidase System in Rats

Laboratory of Nutritional Biochemistry, Department of Agricultural Chemistry, Nagoya University, Nagoya 464-01, Japan

Excess dietary tyrosine (12%) caused hypercholesterolemia in male Wistar rats and significantly increased cytochrome P-450 and b₅ contents. Bile flow and biliary output of total bile acids were significantly increased in rats fed this diet. Biliary output of cholesterol was not significantly altered, whereas that of taurocholic acid was significantly increased. Excess dietary tyrosine significantly decreased the fecal excretion of neutral steroids, whereas total steroid excretion was not significantly changed. The present results indicate that excess dietary tyrosine causes hypercholesterolemia without modifying the fecal total steroid excretion, thus supporting our previous hypothesis that stimulated synthesis of cholesterol is a main reason why excess dietary tyrosine leads to hypercholesterolemia.

KEY WORDS: • rat • tyrosine • hypercholesterolemia • bile acid • cholesterol

¹ Present address: Department of Food Science, Faculty of Agriculture, Gifu University, Gifu 501-11, Japan.

² To whom reprint requests should be addressed.

Manuscript received 10 January 1990. Revision accepted 17 April 1990.