Effects of Urea in Rats Deprived of Arginine

Abstract

The effects on intermediary carbohydrate metabolism of arginine deficiency were studied in male weanling rats fed diets containing only L-amino acids and urea as sources of dietary nitrogen. When arginine was omitted with or without urea substituted for nonessential amino acids (NEAA), food intakes and weight gains were significantly lower during 14 days of feeding. Substituting urea for NEAA produced a significant reduction in weight gain but no reduction in food intake compared to the control diet containing essential amino acids (EAA) with NEAA. Rats fed urea in lieu of NEAA or arginine-deficient diets had a five- to sixfold higher urinary excretion of urea and a two- to threefold increase in blood urea compared to control. Feeding arginine-deficient diets containing NEAA or urea increased urinary excretion of cis-aconitate, trans-aconitate, citrate, isocitrate, α-ketoglutarate and orotate. Rats fed urea with or without arginine excreted less succinate, lactate and α-amino nitrogen in their urine. These results demonstrate that feeding an arginine-deficient diet causes carbamyl phosphate to be shunted toward pyrimidine nucleotide synthesis and also causes significant changes in metabolism via the Krebs cycle. Feeding EAA with or without arginine or urea in lieu of NEAA increased the liver to body weight ratio and reduced liver glycogen.