Tyramine in aged cheese can cause a hypertensive crisis in a patient on a non-selective MAO inhibitor (MAOI). The mechanism is:

• A Tyramine directly stimulates alpha-1 receptors in vascular smooth muscle, causing vasoconstriction
• B Tyramine inhibits catechol-O-methyltransferase (COMT), preventing noradrenaline breakdown and causing accumulation in the synapse
• C Tyramine acts as a weak reuptake inhibitor, blocking the noradrenaline transporter (NET) and causing synaptic NA accumulation
• D Tyramine enters sympathetic nerve terminals via NET and displaces noradrenaline from vesicles. Normally hepatic/intestinal MAO inactivates tyramine; with MAO blocked, tyramine accumulates and triggers a massive NA release ('cheese effect') ✓

Explanation

Tyramine is an indirect sympathomimetic. It is normally inactivated in the gut wall and liver by MAO-A before reaching systemic circulation. When MAO is inhibited, dietary tyramine bypasses this inactivation, enters systemic circulation, is taken up into adrenergic nerve terminals via NET, and displaces stored noradrenaline from vesicles — causing a massive NA release and severe hypertension. This is the classic 'cheese reaction' requiring dietary tyramine restriction on MAOIs.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.