1. In patients with cirrhosis of the liver and in healthy control subjects, the rates of nitrogen flux, protein synthesis and protein breakdown were studied, using a single oral dose of 200 mg of [15N]glycine as a tracer. The nitrogen flux through the amino acid pool was measured separately with both urinary ammonia and urinary urea as end products; the average value was used for further calculations.
2. Subjects were studied in the fed state, both on an adequate and a protein-restricted diet, and also in the fasting state.
3. The rates of protein synthesis were markedly increased in the patients, not only in the fed but also in the fasting state. Protein breakdown rates were increased in the patients in the fed state.
4. The nitrogen balance in steady-state conditions in the fed state was more positive in the patients, while their nitrogen loss in the fasting state was no higher than that of control subjects.
5. A hypothesis is put forward that the high protein requirements of cirrhotic patients could be caused by small and inadequate liver glycogen stores; due to these small stores, gluconeogenesis from amino acids will take place and lead to an extra amino acid loss even during short-term fasting. This increased amino acid loss could explain the elevated protein requirements in cirrhotic patients.