Hypercholesterolemic responses in rabbits to selected groups of dietary essential amino acids

In rabbits, elevation of LDL cholesterol is produced by feeding a cholesterol-free, semipurified diet containing 30% casein amino acid mixture, but not by feeding the same diet containing 14.7% of the casein amino acid mixture, corresponding to a normal level of dietary protein. The hypercholesterolemic response was greater when all essential amino acids except arginine or all ketogenic essential amino acids (lysine, leucine, isoleucine, threonine, phenylalanine, tryptophan and glycine) were selectively fed at three times the normal level. In the present experiments, the same high levels of lysine, leucine and methionine produced a substantial hypercholesterolemia, addition of either isoleucine + threonine or isoleucine + valine did not enhance the effect, and a mixture of threonine, histidine, phenylalanine, tryptophan and glycine gave only a moderate response. A combination of lysine and methionine produced a greater effect than either lysine and leucine or leucine and methionine. Hypercholesterolemic diets containing high levels of lysine and leucine did not cause significantly greater plasma ketone bodies or free fatty acids. Differences in growth rates and ketogenic responses were not generally correlated with hypercholesterolemia.