A patient on a non-selective monoamine oxidase inhibitor attends a party and consumes cheese and red wine. He develops severe throbbing headache and a blood pressure of 220/120 mmHg. Which property of tyramine explains this hypertensive crisis?
- A It releases stored norepinephrine from sympathetic terminals and is normally degraded by MAO in the gut wall and liver ✓
- B It is a direct alpha-1 agonist resistant to metabolism
- C It inhibits neuronal norepinephrine reuptake, raising synaptic norepinephrine concentrations
- D It stimulates adrenal medullary epinephrine secretion through nicotinic receptors
Correct answer: A. It releases stored norepinephrine from sympathetic terminals and is normally degraded by MAO in the gut wall and liver
Explanation
Tyramine is an indirectly acting sympathomimetic taken up by NET into nerve terminals where it displaces stored norepinephrine from vesicles. Normally it undergoes extensive first-pass degradation by MAO in the intestinal wall and liver, so little reaches the circulation. With MAO inhibition it enters the systemic circulation intact and produces massive norepinephrine release. It is not a direct receptor agonist and does not act primarily through reuptake blockade.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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