A depressed patient on tranylcypromine eats aged cheese at a party and develops a throbbing headache with blood pressure of 230/130 mmHg. Which mechanism explains this hypertensive crisis?
- A Tyramine directly stimulates vascular alpha-1 receptors as a superactive analogue of norepinephrine
- B Tyramine inhibits neuronal uptake-1, potentiating circulating catecholamines
- C Unmetabolised dietary tyramine enters sympathetic terminals and displaces stored norepinephrine into the synapse ✓
- D Tyramine is converted centrally to octopamine, a powerful vasoconstrictor false transmitter
Correct answer: C. Unmetabolised dietary tyramine enters sympathetic terminals and displaces stored norepinephrine into the synapse
Explanation
Tyramine is an indirectly acting sympathomimetic taken up into adrenergic nerve endings by NET, where it displaces stored norepinephrine from vesicles, causing massive transmitter release. Normally intestinal MAO destroys dietary tyramine, but MAO inhibitors allow it to reach the systemic circulation intact, producing the 'cheese reaction'. Tyramine itself is a weak direct agonist, and octopamine formed from it is less active than norepinephrine, not more.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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Written and medically reviewed by the StethoPrep medical team.