SummaryWe investigated the fate of exogenous fatty acid in connection with decreased hepatic accumulation and secretion of cholesteryl esters in rats fed diets containing taurine. Providing taurine as 5% of the diet for 14 d significantly decreased concentrations of cholesterol, especially cholesteryl esters in both serum and liver. Ketone body production and incorporation of exogenous [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]oleate into ketone bodies in liver perfusate were consistently higher during a 4-h perfusion period in taurine-fed rats than in control rats. The elevation was accompanied by increased activity of liver mitochondrial carnitine palmitoyltransferase, a rate-limiting enzyme for fatty acid oxidation. Dietary taurine significantly reduced hepatic secretion of cholesteryl ester and decreased incorporation of exogenous oleic acid substrate into this lipid molecule. Further, the extent of reduction in hepatic secretion of cholesteryl ester was closely related to its diminished accumulation in the liver. The conversion pattern of exogenous [1-14 C]oleic acid substrate suggested a decreased esterification-to-oxidation ratio in the taurine group compared with the control. These results suggest that taurine-induced reduction in hepatic accumulation of cholesteryl ester was associated with reduced hepatic secretion of this lipid molecule, and was inversely related to enhanced ketone body production and fatty acid oxidation. Key Words taurine, cholesterol ester secretion, fatty acid oxidation, rat liver Taurine, a sulfur-containing amino acid present in high concentrations in animal tissues, is available from dietary sources and also can be synthesized in vivo from other amino acids. Dietary taurine exhibits various physiologic and pharmacological actions, including hypocholesterolemic and antiatherogenic effects, in experimental animals, especially rats, mice, and Japanese (LAP) quail fed high cholesterol diets ( 1-6 ). These beneficial effects of taurine have recently been reproduced in humans ( 7 , 8 ). Although these effects have attracted attention, the underlying mechanisms are not clearly understood. With regard to the hypocholesterolemic action of dietary taurine, we previously reported that in rats fed high-cholesterol diets, the lowering of serum cholesterol by taurine was partly attributable to a reduced secretion rate of cholesteryl ester by the liver, and that reductions in hepatic secretion rate and in hepatic accumulation of cholesteryl ester were inversely related to increased ketone body production, an index of fatty acid oxidation ( 9 ). This pattern of changes suggested that dietary taurine influences the metabolic fate of fatty acids, specifically whether they undergo esterification or oxidation. However, in that study, we did not assess the relative significance of these two pathways in the metabolism of exogenous fatty acids.We therefore undertook a more detailed examination of fatty acid metabolism using an exogenous [1-14 C]oleic acid, and found for the first time that th...