A patient on phenelzine attends a party and eats aged cheese and red wine. Within 30 minutes he develops severe headache, sweating and a blood pressure of 230/130 mmHg. Which property of tyramine explains this crisis?

• A It directly stimulates vascular alpha-1 receptors at high concentration
• B It activates adrenal medullary nicotinic receptors
• C It inhibits neuronal norepinephrine reuptake
• D It releases norepinephrine from adrenergic nerve terminals as an indirect sympathomimetic ✓

Explanation

Tyramine is an indirectly acting sympathomimetic taken up by the norepinephrine transporter into nerve terminals, where it displaces stored catecholamines from vesicles. Normally intestinal and hepatic monoamine oxidase degrade dietary tyramine before it reaches the circulation, but MAO inhibitors remove this safeguard, so large quantities reach terminals and cause massive norepinephrine release. Option A fails because tyramine is a weak direct agonist at ordinary concentrations; the pressor effect depends entirely on displaced endogenous transmitter.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

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