Acetylcholine

Catecholamines are chemical compounds derived from the amino acid tyrosine that act as hormones or neurotransmitters. They are examples of phenethylamines.

Catecholamines are soluble (~50% loosely bound to plasma protein), and so they can circulate dissolved in blood.

The most abundant catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. They are produced mainly from the adrenal medulla and the postganglionic fibers of the sympathetic nervous system. Adrenaline acts as a neurotransmitter in the central nervous system and as a hormone in the blood circulation. Noradrenaline is primarily a neurotransmitter of the peripheral sympathetic nervous system but is also present in the blood (mostly through "spillover" from the synapses of the sympathetic system).

High catecholamine levels in blood are associated with stress. Catecholamines cause general physiological changes that prepare the body for physical activity (fight-or-flight response). Some typical effects are increases in heart rate, blood pressure, and blood glucose levels. Some drugs, like tolcapone (a central COMT-inhibitor), raise the levels of all the catecholamines.

Catecholamines have the distinct structure of a benzene ring with two hyroxyl groups and an amine group. They have a half-life of approximately a few minutes when cirulating in the blood and are formed from the amino acid, Tyrosine.