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Catecholamines

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Adrenaline
epinephrine
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Norepinephrine structure
norepinephrine
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Dopamine
dopamine
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Catecholamines are sympathomimetic[1] "fight-or-flight" hormones that are released by the adrenal glands in response to stress.[2] They are part of the sympathetic nervous system.

They are called catecholamines because they contain a catechol group, and are derived from the amino acid tyrosine.[3]. Some of them are biogenic amines. Catecholamines are water-soluble and are 50% bound to plasma proteins, so they circulate in the bloodstream.


The most abundant catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine, all of which are produced by phenylalanine and tyrosine. Tyrosine is created from phenylalanine by hydroxylation by the enzyme phenylalanine hydroxylase (tyrosine is also ingested directly from dietary protein). Tyrosine is then sent to catecholamine-secreting neurons. Here, many kinds of reactions convert it to dopamine, to norepinephrine, and eventually to epinephrine.[4] Catecholamines are hormones that are released by the adrenal glands in situations of stress such as psychological stress or low blood sugar levels.[5]

ProductionEdit

LocationEdit

Catecholamines are produced mainly by the chromaffin cells of the adrenal medulla and the postganglionic fibers of the sympathetic nervous system. Dopamine, which acts as a neurotransmitter in the central nervous system, is largely produced in neuronal cell bodies in two areas of the brainstem: the substantia nigra and the ventral tegmental area.

SynthesisEdit

Dopamine was the first catecholamine to be synthesized. Norepinephrine and epinephrine, in turn, are derived from further modifications of dopamine.

File:Catecholamines biosynthesis.svg
Catecholamine synthesis.

Catecholamine synthesis is inhibited by alpha-Methyltyrosine, by inhibiting tyrosine-3 monooxygenase.[6]

FunctionEdit

ModalityEdit

Two catecholamines, norepinephrine and dopamine, act as neurotransmitters in the central nervous system and as hormones in the blood circulation. The catecholamine norepinephrine is 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, which can be induced from psychological reactions or environmental stressors such as elevated sound levels, intense light, or low blood sugar levels.

Extremely high levels of catecholamine (also known as catecholamine toxicity) can occur in central nervous system trauma due to stimulation and/or damage of nuclei in the brainstem, in particular those nuclei affecting the sympathetic nervous system. In emergency medicine, this occurrence is widely known as catecholamine dump.

Extremely high levels of catecholamine can also be caused by neuroendocrine tumors in the adrenal medulla, a treatable condition known as pheochromocytoma.

EffectsEdit

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, blood glucose levels, and a general reaction of the sympathetic nervous system. Some drugs, like tolcapone (a central COMT-inhibitor), raise the levels of all the catecholamines.

StructureEdit

Catecholamines have the distinct structure of a benzene ring with two hydroxyl groups, an intermediate ethyl chain, and a terminal amine group.

DegradationEdit

They have a half-life of approximately a few minutes when circulating in the blood.

Monoamine oxidase (MAO) is the main enzyme responsible for degradation of catecholamines.

Methamphetamine and MAOIs bind in order for MAOs to inhibit their action of breaking down catecholamines. This is primarily the reason why the effects of amphetamines have a longer lifespan than those of cocaine and other substances. Amphetamines not only cause a release of dopamine, epinephrine, and norepinephrine into the blood stream but also keep it working there for a long time.

See alsoEdit

ReferencesEdit

  1. Template:DorlandsDict
  2. University of California, San Diego, Health Library, catecholamines.
  3. Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). Neuroscience. 4th ed, 137–8, Sinauer Associates.
  4. [1]
  5. "Hypoglycemia" by Ronald Hoffman, M.D., July 1999, The Holistic M.D.
  6. wrongdiagnosis.com - Description of Alpha-Methyltyrosine

External linksEdit

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