Urinary p-tyramine in hereditary tyrosinemia: II. Origin of urinary p-tyramine.

1. A patient with hereditary tyrosinemia (tyrosinosis) was given oral loads of p-tyramine and tyrosine with and without medication (neomycin) to investigate the respective roles of intestinal bacteria and tissues in accounting for the origin of urinary p-tyramine. 2. The excretion of a high circulating level of p-tyramine following an oral load of p-tyramine in a patient with hereditary tyrosinemia (tyrosinosis) was as conjugated p-hydroxyphenylacetic acid (p-HPAA) and conjugated p-tyramine. 3. Both intestinal bacterial activity and tissue decarboxylation appeared to account for urinary p-tyramine in this patient following an oral load of tyrosine. 4. Sterilization of the gut by oral neomycin and a second load of oral tyrosine further supported a predominate role for tissue decarboxylation in the origin of urinary p-tyramine. 5. The data suggested that a major route of tyrosine metabolism in man may be via tissue decarboxylation of tyrosine.