Maximal Rates of Excretion and Synthesis of Urea in Normal and Cirrhotic Subjects

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Abstract

When normal individuals eat 0.33 g protein N/kg body weight (BW)¾ per day, they excrete 10-15 mg urea N/h per kg BW¾. If they now ingest (at 0 h) 0.27 (dose A), 0.40 (dose B), 0.53 (dose C), 0.94 (dose D), or 1.33 (dose E) g protein N/kg BW¾ (in the form of casein, ovalbumin, or lactalbumin), the rate of urea N excretion accelerates within 4 h. At dose C a maximal rate of urinary urea N excretion (MRUE) is reached, which averages 55 mg urea N/h per kg BW¾ and which persists for 16 h. Higher doses of protein do not further accelerate urea excretion, but prolong the duration of MRUE to 28 h (after dose E). Blood urea N (BUN) rises by 7-20 mg/100 ml during the first 8 h after dose C to E, and remains stable within ±5 mg/100 ml during the ensuing 8-28 h of MRUE. Each increment of protein above dose C causes a further increment in plasma α-amino N. During infusion of free amino acids at a rate of 110 or 165 mg amino acid N/h per kg BW¾ for 12 h, rate of urea excretion increases to the MRUE value produced by dose C-E of oral protein.

Authors

Daniel Rudman, Thomas J. DiFulco, John T. Galambos, Robert B. Smith III, Atef A. Salam, W. Dean Warren