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Growth and Metabolism of Rats Fed Nonprotein Nitrogen Diets Supplemented with Nicotinamide, Succinate and Pyridoxine

Department of Animal Science, Cornell University, Ithaca, New York 14850

The effects of adding nicotinamide, pyridoxine and sodium succinate to purified L-amino acid diets, containing ammonium acetate or urea in place of the nonessential amino acids, were evaluated in the rat. Growth, food intake, liver and intestinal isocitrate dehydrogenase activity, and blood levels of urea, ammonia, glucose and amino acids were determined after 14 days of feeding. During this period, growth (g/day) was 1.9 for the negative control diet (containing only the essential amino acids), and 3.7 and 3.5 when nonessential amino acids and ammonium acetate, respectively, were added. Replacing the nonessential amino acids with ammonium acetate or urea increased blood urea concentrations two- to threefold. Plasma tyrosine, phenylalanine and histidine concentrations were lower when ammonium acetate replaced the nonessential amino acids. Replacement of nonessential amino acids with ammonium acetate or addition of pyridoxine did not alter liver NADP-isocitrate dehydrogenase activity while mitochondria of intestinal mucosa from ammonium acetate-fed rats tended to be lower in NAD-isocitrate dehydrogenase activity. Factors other than decreased glycolytic or Krebs cycle enzymes in the liver appear responsible for the reduced growth rate when dietary nonessential amino acids were replaced with ammonium acetate or urea. The present experiments further suggest that replacement of nonessential amino acids with ammonium acetate retarded growth by altering the amino acid supply to the tissues. Evidence suggesting that metabolism within the intestinal mucosa was more severely deranged than in the liver when ammonium acetate replaced nonessential amino acids is also presented.

KEY WORDS: • nonprotein nitrogen • ammonia • amino acids • liver enzymes • intestinal mucosa enzymes

¹ Present Address: Department of Nutrition, University of California, Davis, Calif. 95616.

Manuscript received 5 July 1972.