TYROSINE METABOLISM IN CIRRHOSIS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 94  (6) , 832-840
Abstract
The enzyme defect responsible for tyrosinemia in cirrhotic patients was studied. The principal hepatic degradation pathway for tyrosine, tyrosine .fwdarw. p-hydroxyphenylpyruvic acid [PHPA] .**GRAPHIC**. homogentisic acid .**GRAPHIC**. CO2 was studied in 18 cirrhotic patients and 8 controls. The classic method employed in elucidation of hereditary tyrosinosis was used. Metabolic intermediates on the pathway were measured in the basal state, and following oral loading doses (50 mg/kg body wt) of tyrosine, PHPA and homogentisic acid. Cirrhotic patients showed a significant increase (P = 0.005) in fasting plasma tyrosine and in basal PHPA excretion and impaired tolerance to all 3 metabolites whem compared to normals. Of the 18 cirrhotic patients, 15 showed tyrosine intolerance which was not accompanied by change in distal metabolites compared to their basal levels. Nevertheless 13 of the 18 did exhibit intolerance of either PHPA or homogentisic acid. In contrast to the single complete defect in hereditary disorders of tyrosine metabolism, cirrhotic patients have partial defects at tyrosine transaminase, PHPA oxidase, and homogentisic acid oxidase, the initial step being rate-limiting.

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