• 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.