A 52-year-old man on tranylcypromine attends a party and shortly after eating aged cheese develops throbbing headache and a blood pressure of 230/130 mmHg. The mechanism of this hypertensive crisis is:
- A Displacement of stored norepinephrine from sympathetic vesicles by tyramine, an indirectly acting sympathomimetic ✓
- B Direct alpha-1 agonism by tyramine metabolites
- C Accumulation of serotonin due to neuronal uptake blockade
- D Potentiation of circulating epinephrine by reduced hepatic COMT activity
Correct answer: A. Displacement of stored norepinephrine from sympathetic vesicles by tyramine, an indirectly acting sympathomimetic
Explanation
Tyramine in fermented foods is normally degraded by MAO in the gut wall and liver. With non-selective MAO inhibition, it reaches the circulation, is taken up by noradrenergic terminals via NET and displaces vesicular norepinephrine into the synapse, producing massive sympathetic discharge. This is identical to the mechanism of amphetamine-type indirect agonists. It is displacement of preformed transmitter, not direct receptor agonism or altered COMT handling.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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