Tyramine

Overview
In organic chemistry tyramine (4-hydroxy-phenethylamine, para-tyramine, p-tyramine) is a monoamine compound derived from the amino acid tyrosine.

Occurrence
Tyramine occurs widely in plants and animals and is metabolized by the enzyme monoamine oxidase. In foods, it is often produced by the decarboxylation of tyrosine during fermentation or decay. Foods containing considerable amounts of tyramine include meats (fish, poultry, and beef) that are potentially spoiled or pickled, aged, smoked, fermented, or marinated, most pork (except country [cured ham), chocolate, alcoholic beverages, and fermented foods such as most cheeses (except ricotta, cottage cheese, cream cheese), sour cream, yogurt, tofu, miso soup, soy sauce and soy bean condiments, teriyaki sauce, shrimp paste, sauerkraut, broad (fava) beans, green bean pods, Italian flat (Romano) beans, Chinese (Snow) pea pods, avocados, bananas, eggplant, figs, red plums, raspberries, peanuts, Brazil nuts, coconuts, processed meat, yeast, and red wine.

Metabolism
In humans, if monoamine metabolism is compromised by the use of monoamine oxidase inhibitors (MAOIs) and foods high in tyramine are ingested, a hypertensive crisis can result as tyramine can cause the release of stored monoamines, such as dopamine, norepinephrine, epinephrine. The first signs of this were discovered by a neurologist who noticed his wife, who at the time was on MAOI medication, had severe headaches when eating cheese. For this reason, the crisis is still called the "cheese syndrome," even though other foods can cause the same problem.

Effects
A large dietary intake of tyramine (or a dietary intake of tyramine while taking MAO inhibitors) can cause the 'tyramine pressor response,' which is defined as an increase in systolic blood pressure of 30 mmHg or more. The displacement of norepinephrin(noradrenaline) from neuronal storage vesicles by acute tyramine ingestion is thought to cause the vasoconstriction and increased heart rate and blood pressure of the pressor response.

However, if one has had repeated exposure to tyramine, there is a decreased pressor response; Tyramine is degraded to octopamine, which is subsequently packaged in synaptic vesicles with norepinephrin(noradrenaline). Therefore, after repeated tyramine exposure, these vesicles contain an increased amount of octopamine, and a relativley reduced amount of norepinephrin(noradrenaline). Therefore, when these vesicles are secreted upon tyramine ingestion, there is a decreased pressor response, as less norepinephrin(noradrenaline) is secreted into the synpase, and octopamine does not activate alpha or beta adrenoceptors.

The possibility that tyramine acts directly as a neurotransmitter was revealed by the discovery of a G protein-coupled receptor with high affinity for tyramine, called TA1. The TA1 receptor is found in the brain as well as peripheral tissues, including the kidney. The existence of a receptor with high affinity for tyramine supports the hypothesis that tyramine may also act directly to affect blood pressure regulation.

Migraine
Dietary tyramine intake has also been associated with migraine in select populations, leading many sufferers to restrict foods high in tyramine. Reports on the tyramine-migraine link have been both affirmed and denied. A recent review article found that all past studies affirming a migraine-tyramine connection were scientifically inconclusive, and noted several studies showing no connection. Two studies validated as scientifically sound reported no connection in the population evaluated.