A 42-year-old man on phenelzine attends a party and consumes red wine and aged cheese. He develops throbbing headache, profuse sweating, and blood pressure of 220/120 mmHg. Which property of tyramine explains this hypertensive crisis?
- A It is a direct alpha-1 agonist resistant to metabolism
- B It is an indirect sympathomimetic that releases stored norepinephrine from nerve terminals ✓
- C It inhibits norepinephrine reuptake at the transporters
- D It stimulates adrenal medullary chromaffin cells directly
Correct answer: B. It is an indirect sympathomimetic that releases stored norepinephrine from nerve terminals
Explanation
Tyramine is an indirectly acting sympathomimetic taken up into sympathetic nerve terminals where it displaces stored norepinephrine. Normally gut and liver monoamine oxidase degrade dietary tyramine before it reaches the circulation, but MAO inhibition allows large amounts to reach adrenergic neurons and trigger massive catecholamine release. Phentolamine is the treatment of choice. It does not act as a direct agonist or a reuptake blocker.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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