The N Balance Index of Low-Valine Amino Acid Mixtures and of Whole Egg Protein in the Adult Rat

Abstract

Nitrogen balance was determined on adult rats receiving amino acid mixtures or whole egg protein as a source of nitrogen. Each experiment included a 7-day period on a N-free diet and a 7-day period on an amino acid mixture or an egg protein diet that supplied about half the maintenance requirement of nitrogen; this was followed by another 7-day period on a similar diet but with the nitrogen intake doubled. These diets were fed by stomach tube twice daily so that each rat received the same quantity of diet every day. The nitrogen balance index of ingested nitrogen, K′, for the complete amino acid mixtures is 0.99; for egg protein K′ = 1.18. When valine is reduced to one-sixth, or less, of the amount present in the complete amino acid mixture, K′ = 0.51 or less. Such a diminution of valine, therefore, reduces significantly the utilization of the nitrogen of the whole mixture. A relationship is described between valine nitrogen intake and nitrogen balance. It is estimated that the adult rat, under these conditions, requires 2.1 mg of nitrogen from l-valine and 4.2 mg from dl-valine per day per kilogram^3/4. Using the same relationship, it is estimated that the fraction of a gram of nitrogen that must be supplied as valine, in order to cause the rentention of 1 gm of nitrogen by the rat, is 0.017 for l-valine and 0.038 for dl-valine.