Tyramine (4-Hydroxyphenethylamine; para-Tyramine; Mydrial, Uteramin) is a naturally occurring monoamine compound and trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine (dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline)) releasing agent. Notably, however, it is unable to cross the blood-brain-barrier (BBB), resulting in only non-psychoactive peripheral sympathomimetic effects. When tyramine rich foods are ingested in conjunction with a monoamine oxidase inhibitor (MAOI), tyramine is responsible for the so-called "cheese effect" sometimes seen with their use.
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 norepinephrine (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. In severe cases, adrenergic crisis can occur.
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 norepinephrine (noradrenaline). Therefore, after repeated tyramine exposure, these vesicles contain an increased amount of octopamine and a relatively reduced amount of norepinephrine (noradrenaline). When these vesicles are secreted upon tyramine ingestion, there is a decreased pressor response, as less norepinephrine (noradrenaline) is secreted into the synapse, and octopamine does not activate alpha or beta adrenergic receptors.
When using a MAO inhibitor (MAOI), the intake of approximately 10 to 25 mg of tyramine is required for a severe reaction compared to 6 to 10 mg for a mild reaction.
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.
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 2007 review published in Neurological Sciences presented data showing that migraine and cluster headaches are characterised by an increase of circulating neurotransmitters and neuromodulators (including tyramine, octopamine and synephrine) in the hypothalamus, amygdala and dopaminergic system.
Category:Migraine Category:Monoamine oxidase inhibitors Category:Monoamine releasing agents Category:Phenethylamines
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