A patient on a monoamine oxidase inhibitor (MAOI) for depression ingests tyramine-rich aged cheese and develops a hypertensive crisis. The mechanism is best described as:

• A Tyramine directly stimulates vascular alpha-1 receptors
• B MAO inhibition allows gut-absorbed tyramine to release large amounts of norepinephrine from terminals ✓
• C Tyramine inhibits COMT, prolonging catecholamine half-life
• D MAOI increases sensitivity of postsynaptic alpha-2 receptors to tyramine

Explanation

Normally tyramine is metabolized by MAO-A in the gut wall and liver (first-pass), preventing systemic absorption. When MAO is inhibited, tyramine reaches systemic circulation and acts as an indirect sympathomimetic, entering adrenergic nerve terminals and displacing large stores of norepinephrine. The massive release causes severe hypertension — the 'cheese reaction.' Tyramine itself has no significant direct adrenoceptor affinity.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.