Tyramine is a naturally occurring monoamine compound and trace amine derived from the amino acid tyrosine. Tyramine occurs widely in plants and animals, and is metabolized by the enzyme monoamine oxidase. Tyramine is an alpha-adrenergic agonist. Hypertension can occur, from ingestion of tyramine-rich foods in conjunction with monoamine oxidase inhibitors. 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 TAAR. It exhibits sympathomimetic effects by causing the release of endogenic norepinephrine. It has been used in mydriatic eyedrops. This has been said to reduce the intraocular pressure in rabbits and in some patients with open-angle glaucoma.