Urinary Excretion of Amino Acids and Peptides by Dogs Fed Protein Hydrolysates or Amino Acids

Abstract

The urinary excretion of amino acids by dogs was negligible during a 4-day period of oral feeding of protein hydrolysates or amino acid mixtures. After intravenous administration over a period of one hour per day, the loss of free amino acids in the urine ranged from 5 to 20% and there was a decrease in nitrogen retention of approximately 25%. When the daily allotment was given by vein in only 15 min., the loss of amino acids in the urine increased 10 to 15% and the utilization of nitrogen decreased approximately 60%, due to greater excretion of urea and ammonia nitrogen. After oral feeding of preparations containing peptides, 2 to 11% of the peptide fraction was lost in the urine. After infusion by vein during a one-hour period an average of 30% of the peptides was excreted, in contrast to only 14% of the free amino acids of these preparations. A 4-fold increase in the rate of infusion resulted in no additional loss of peptides in the urine. One preparation, which was utilized approximately as well as casein when administered orally, was found to have no biological value in terms of nitrogen retention when given intravenously. This was apparently related to the excessive urinary loss of its peptides (45%) and its amino acids (12%). The degree of utilization of protein hydrolysates and amino acid mixtures depends upon the method of feeding and upon the rate of infusion.