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Effects of Excess Dietary Tyrosine or Certain Xenobiotics on the Cholesterogenesis in Rats1

Satoshi Nagaoka, Hisanori Masaki, Yoritaka Aoyama and Akira Yoshida2

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

Comparison of the effects of excess dietary tyrosine, DDT, chlorobutanol (Chloretone) or butylated hydroxyanisole (BHA) on serum cholesterol, hepatic activities of the rate-limiting enzyme of cholesterol synthesis,3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) and in vivo rates of the hepatic cholesterol synthesis measured by 3H2O incorporation were investigated in rats. Serum cholesterol concentration was significantly higher in rats fed the DDT, chlorobutanol, BHA or excess tyrosine diets than in rats fed the control diet for 7 days. Serum cholesterol concentration remained higher compared to control rats when excess tyrosine was fed for 21 d. When rats were fed a basal diet after feeding a tyrosine excess diet for 2 wk, liver weight and serum cholesterol level returned to normal within 7 d. The incorporation of 3H2O into liver cholesterol and the activity of liver 3-hydroxy-3-methylglutaryl coenzyme A reductase were greater in rats fed excess tyrosine or certain xenobiotics than in control rats. Present results suggested that the increase in serum cholesterol concentration due to excess dietary tyrosine or certain xenobiotics is mainly attributable to the stimulation of liver cholesterol synthesis.

KEY WORDS: • tyrosine • DDT • chlorobutanol • butylated hydroxyanisole • cholesterol • xenobiotics • hypercholesterolemia

1 Supported in part by a grant from the Nissan Science Foundation and Elizabeth Arnold Fuji Foundation, Japan.

2 To whom reprint requests should be addressed.

Manuscript received 25 June 1985. Revision accepted 7 January 1986.






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