Kinetics of intravenous administered L-phenylalanine in patients with cirrohosis of the liver.

The metabolism of intravenously administered L-phenylalanine has been studied in 13 patients with cirrhosis of the liver and in 17 control subjects. The decline in the plasma phenylalanine concentration followed a biexponential curve and the kinetics could be evaluated assuming a two-compartment model. The volume of the central compartment was reduced in the cirrhotic patients, reflecting a diminished liver pool size. The total phenylalanine clearance was lower in the cirrhotic patients, due mainly to a reduction of the liver cell mass or to changes in the intrahepatic membrane permeability and only to a minor extent to a reduced hepatic blood flow. The elimination rate constant from the central compartment was similar in both groups, suggesting that the remaining liver cells, had a normal capacity to hydroxylate phenylalanine to tyrosine. There was considerable overlapping in the kinetic parameters between the two groups, and even in patients with well established cirrhosis an apparently normal phenylalanine metabolism was observed.