Effect of excess dietary lysine on plasma lipids of the chick.

Feeding diets with 4% L-lysine to the chick produces an elevation of plasma lipids which does not occur when feeding an excess of any other amino acid. Experiments were conducted to determine whether lysine-induced hyperlipidemia is secondary to the antagonistic effect of lysine on arginine or to the anorexia which accompanies lysine feeding, and in addition, whether the lysine-induced hypercholesterolemia is affected by chick age. In all experiments gain and food intake were reduced by feeding chicks 4% lysine. Plasma cholesterol and triglyceride were elevated, but high-density-lipoprotein cholesterol, as a percentage of total, was reduced. Addition of dietary arginine up to 4% failed to reverse the depression in performance and elevation of plasma lipids. Pair-feeding the control diet to the amount consumed by lysine-fed chicks did not elevate plasma lipids above control levels. Thus, lysine-induced hyperlipidemia is not mediated by the antagonistic effect of lysine on arginine nor by the effect of lysine on food intake. The high-lysine diet prevented the normal decline in plasma cholesterol expected with advancing age of chicks. Preliminary results suggested that excess lysine stimulated cholesterol biosynthesis.