Effects of Altering the Proportions of Essential to Nonessential Amino Acids on Growth and Plasma Amino Acid Levels in the Rat

Abstract

The quantitative relationship between essential and nonessential amino acids was studied in weanling rats fed L-amino acid diets supplying either 2.23 or 2.90% dietary nitrogen for 14 days. The proportion of total essential to total nonessential amino acids was varied, and weight gains, food consumption, and free amino acids in plasma after a 15- to 18-hour fast were measured. For the 2.23% dietary series, maximum growth was achieved when the ratio of total essential amino acids per gram total dietary nitrogen (E/TN ratio) was between 3.37 and 4.71; for the 2.90% N series, it was achieved when the E/TN ratio was between 3.03 and 4.04. Increased proportions of dietary total essential amino acids resulted in increases in plasma threonine, lysine, phenylalanine, and valine as maximum growth rate was obtained. At the highest essential amino acid intake, growth rate declined, and the levels of all these plasma amino acids except threonine decreased.