Nitrogen metabolism and growth in experimental uremia

Growth in length, weight gain and gain of body nitrogen were compared in rats with stable long-term uremia (U) resulting from subtotal two-stage nephrectomy with irradiation of residual parenchyma, in sham-operated pair-fed control rats (PFC) and in ad libitum fed control rats (LC). Growth in length and weight gain were considerably lower in U than in LC rats, reflecting mainly diminished intake of food in uremia. However, they were also significantly lower in U than in PFC despite identical intake of food, pointing to a specific adverse effect of uremia on growth. Whole body dry matter, whole body nitrogen and weight of a reference muscle (triceps surae) were significantly lower in U than in PFC animals, showing that dietary nitrogen and/or energy are less efficiently utilized for protein synthesis in U animals. Diminished net nitrogen retention was paralleled by increased urinary nitrogen loss (excretion of urea, alpha-amino nitrogen, protein, and creatinine). Within the precision of the method used, no significant difference of oxygen consumption between U and PFC animals could be demonstrated. The plasma amino acid pattern was deranged and the tyrosine/phenylalanine ratio was decreased despite no change in hepatic phenylalanine hydroxylase. The findings document increased nitrogen and/or energy cost of growth in rats with stable chronic uremia; this finding agrees with previous observations of disturbed protein metabolism and hypercatabolism in experimental uremia.