American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What effect does metyrosine have on catecholamine synthesis?

1. Increases catecholamine production

2. Inhibits catecholamine synthesis

3. Stimulates neurotransmitter release

4. None of the above

The correct answer is: Inhibits catecholamine synthesis

Metyrosine is a medication that functions as a competitive inhibitor of the enzyme tyrosine hydroxylase, which is the rate-limiting step in the synthesis of catecholamines such as dopamine, norepinephrine, and epinephrine. By inhibiting this enzyme, metyrosine effectively reduces the production of these important neurotransmitters. This mechanism is particularly valuable in clinical settings where there is a need to decrease catecholamine levels, such as in cases of pheochromocytoma (a tumor that secretes excess catecholamines) or during preparation for surgical procedures. The other choices suggest either an increase in production or stimulation of release. However, since metyrosine specifically inhibits the synthesis pathway of catecholamines, it does not increase production or stimulate release, making the option that indicates inhibition the only correct response.