Essential amino acids in relation to hypercholesterolemia induced in rabbits by dietary casein

Rabbits fed a cholesterol-free, semi-purified diet containing 25% casein amino acids (25% AA) for 2 wk had significantly higher serum total and low density lipoprotein (LDL) cholesterol levels than animals fed the same diet containing 11.2% casein amino acids (11.2% AA). These results were similar to those obtained by feeding diets containing 27% and 12% casein, respectively. When rabbits were fed the 11.2% AA diet supplemented with essential amino acids to the 25% level (11.2% AA + essential AA), their LDL cholesterol level was significantly higher than that in animals fed the 11.2% AA diet supplemented with nonessential amino acids to the 25% level (11.2% AA + nonessential AA). LDL protein and phospholipid levels were significantly higher in rabbits fed the 25% AA diet than in those fed 11.2% AA and tended to be elevated in animals fed 11.2% AA + essential AA compared to those fed 11.2% AA + nonessential AA. Fecal excretion of bile acids and cholesterol was similar with all dietary regimens, and the level of liver lipids showed no correlation with the degree of hypercholesterolemia produced by dietary amino acid mixtures.