Effect of dietary long-chain fatty acids on the rates of cholesterol turnover processes, cholesterol origin and distribution in the rat intestinal lumen.

Adult male rats were fed a semi-purified diet containing 20 p. 100 of lard or homogeneous triglycerides (tripalmitin, tristearin, triolein, trierucin) for 4 months. The rates of the processes (absorption, synthesis, degradation into bile acids, fecal and urinary excretion) involved in cholesterol turnover were measured using the isotope equilibrium method. The absorption coefficient of dietary cholesterol attained 71 +/- 3 p. 100 in rats fed the lard diet. It was unchanged in rats eating the triolein (73 +/- 3 p. 100) or tripalmitin (75 +/- 4 p. 100) diet but was drastically reduced in those receiving trierucin (45 +/- 1 p. 100) or tristearin (34 +/- 1 p. 100). Some functional and topological aspects of cholesterol absorption are discussed. Four to 6 times more endogenous cholesterol was found in the intestinal lumen of rats fed trierucin than in that of rats receiving a normolipid diet. Micelle cholesterol increase was also proportionally less. There was no direct relationship between the quantity of cholesterol found in the micelles and that absorbed. Dietary cholesterol was absorbed in the second as well as in the first half of the intestine, while the proportions of micellar cholesterol decreased continuously from the jejunum to the ileum. The rates of fecal excretion and fecal external secretion were inversely correlated to the absorption coefficient of dietary cholesterol, as has been previously described. The internal secretion was stimulated two to threefold in rats fed tristearin (22.3 +/- 0.7 mg/d), tripalmitin (28.4 +/- 4.6 mg/d) and trierucin (33.2 +/- 2.8 mg/d) as compared to rats fed lard (12.5 +/- 0.6 mg/d) or triolein (14.4 +/- 1.2 mg/d). Feeding a tripalmitin or a trierucin diet greatly increased cholesterogenesis (probably in the liver), while tristearin stimulated non-hepatic cholesterogenesis. The variations in daily bile acid elimination may be seen as an adaptive parameter, modulating its rate according to the cholesterol supply (absorption and synthesis).