To investigate body protein turnover and the pathogenesis of increased
concentration of plasma phenylalanine in liver cirrhosis, we have studied
phenylalanine and leucine kinetics in cirrhotic (diabetic and nondiabetic)
patients, and in normal subjects, both in the postabsorptive state and during a
mixed meal, using combined intravenous and oral isotope infusions. Postabsorptive
phenylalanine concentration and whole body rate of appearance (Ra) were
approximately 40% greater (P < 0.05) in patients than in controls. Leucine
concentrations were comparable, but intracellular leucine Ra was also increased
(P < 0.05), suggesting increased whole body protein breakdown. Postprandial
phenylalanine Ra was also greater (P < 0.05) in the patients. This difference was
due to a diminished fractional splanchnic uptake of the dietary phenylalanine
(approximately 40% lower in the cirrhotics vs. controls, P < or = 0.05).
Postprandial leucine Ra was also increased in the patients, but splanchnic uptake
of dietary leucine was normal. Thus both increased body protein breakdown and
decreased splanchnic extraction of dietary phenylalanine can account for the
increased phenylalanine concentrations in liver cirrhosis
