Urea synthesis after oral protein ingestion in man

In an attempt to assess hepatic functional capacity, hourly urea production, and corresponding serum amino acid concentrations after the ingestion of single protein meals (60, 120, and 240 g of protein) were evaluated in 18 normal subjects and in 8 patients with liver disease. In normal subjects, the relationship between urea production and serum amino acid concentration was linear (urea production in milligram urea nitrogen/kilogram lean body mass/hour = 6.3 times mg amino acid nitrogen/100 ml minus 20.5 SE of the estimate 6.9, r = 0.74, P less than 0.001), and variation of protein intake from 50 to 150 g/day for 3 days before testing did not change this relationship. The patients demonstrated impairment of urea synthesis proportional to the clinical severity of their liver disease. The potential clinical applications of these findings need to be determined.