Elimination of infused amino acids from plasma of control subjects and of patients with cirrhosis of the liver

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Abstract
In four control subjects and four patients with cirrhosis of the liver a multiple amino acid mixture was infused for 12 h at a constant rate of 68 and 56 μmol α‐amino N/s, respectively. Before infusion the plasma amino N concentration was 2·4 pL 0·2 (mean pL SD) mmol/l in control subjects and 3·5 pL 0·7 mmol/l in patients (P 0·025). The concentration of alanine, proline, arginine, tyrosine, and citrulline was significantly increased in the cirrhosis group. 12 h after the infusion began approximately constant amino N concentrations of 11·4 pL 1·8 mmol/l in controls and 13·7 pL 3·9 mmol/l in patients were attained, and the urea N synthesis rate was 63 pL 17 and 44 pL 8 μmol/s, respectively (P < 0·05). After correction for loss of amino acids in urine this means that on the average 94 per cent of the N load was recovered as urea. The plasma clearance of infused amino acids, calculated as the ratio between infusion rate and steady state concentration, was 6·0 pL 1·2 and 4·1 pL 0·9 ml/s for amino N in the control and cirrhosis group, respectively (P < 0·025). The clearance of individual amino acids ranged between 2·5 and 28 ml/s. The clearance of most amino acids was decreased in the cirrhosis group, and of glycine, proline, lysine, threonine, and arginine significantly so (P < 0·05), reflecting accumulation of amino acids in patients. This indicates that a primary defect in the conversion of amino N in cirrhosis is the reduced urea synthesis.