Catecholamine Synthesis and Tyrosine Catabolism

  • Tyrosine to DOPA by tyrosine hydroxylase is rate-limiting.
  • Norepinephrine is converted in the adrenal medulla to epinephrine by phenylethanolamine-N-methyltransferase, which is upregulated by cortisol. Pituitary resection will lead to loss of ACTH, Cortisol & subsequent reduced epinephrine levels.
  • Epinephrine is converted to metanephrine by COMT.
  • Metanephrine & normetanephrine are converted by monoamine oxidase (MAO) to vanillylmandelic acid.


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