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{{BioPsy}}
'''Epinephrine''' ([[International Nonproprietary Name|INN]]) or '''adrenaline''' ([[British Approved Name|BAN]]) is a [[hormone]] and a [[neurotransmitter]]. The [[Latin]] roots ''ad-''+''renes'' and the [[Greek language|Greek]] roots ''epi-''+''nephros'' both literally mean "on/to the [[kidney]]" (referring to the [[adrenal gland]], which secretes epinephrine). Epinephrine is sometimes shortened to '''epi''' in medical [[jargon]].
 
   
  +
{{drugbox |
Epinephrine is a [[catecholamine]], a sympathomimetic monoamine derived from the [[amino acid]]s [[phenylalanine]] and [[tyrosine]]. Its '''[[ATC code]]''' is C01CA24.
 
  +
| width = 200
  +
| image = Adrenaline_chemical_structure.png
  +
| image2 = Epinephrine-3d-CPK.png
  +
|imagename=''(R)''-(−)-<small>L</small>-Epinephrine or ''(R)''-(−)-<small>L</small>-adrenaline
  +
|IUPAC_name = ''(R)''-4-(1-hydroxy-<br />2-(methylamino)ethyl)benzene-1,2-diol
  +
|CAS_number = 51-43-4
  +
|ATC_prefix = A01
  +
|ATC_suffix = AD01
  +
|ATC_supplemental = {{ATC|B02|BC09}} {{ATC|C01|CA24}} {{ATC|R01|AA14}} {{ATC|R03|AA01}} {{ATC|S01|EA01}}
  +
|PubChem = 838
  +
|DrugBank = APRD00450
  +
|C = 9 | H = 13 | N = 1 | O = 3
  +
|molecular_weight = 183.204 g/mol
  +
|bioavailability = Nil (oral)
  +
|metabolism = [[synapse|adrenergic synapse]] ([[Monoamine oxidase|MAO]] and [[Catechol-O-methyl transferase|COMT]])
  +
|elimination_half-life = 2 minutes
  +
|excretion = n/a
  +
|pregnancy_AU = A
  +
|pregnancy_US = C
  +
|legal_AU = S4
  +
|legal_US = Rx-only
  +
|routes_of_administration = [[intravenous|IV]], [[intramuscular|IM]], [[endotracheal tube|endotracheal]]
  +
}}
   
  +
'''Adrenaline redirects here'''
[[William Horatio Bates|William Bates]] reported in the New York Medical Journal in May 1886 the discovery of a substance produced by the suprarenal gland. Epinephrine was isolated and identified in [[1895]] by [[Napoleon Cybulski]], [[Poland|Polish]] [[physiology|physiologist]]. The discovery was repeated in [[1897]] by [[John Jacob Abel]]. [[Jokichi Takamine]] discovered the same hormone in [[1900]], without knowing about the previous discovery; but, in later years, counterevidence is shown from the experiment note that Kaminaka leaves that the Takamine team is the discoverer of first adrenaline. It was first artificially synthesized in [[1904]] by [[Friedrich Stolz]].
 
  +
 
'''Epinephrine''' ([[International Nonproprietary Name|INN]]) ([[International Phonetic Alphabet|IPA]]: {{IPA|[ˌɛpɪˈnɛfrən]}}) or '''adrenaline''' (European Pharmacopoeia and British Approved Name|BAN) ([[International Phonetic Alphabet|IPA]]: {{IPA|[əˈdrɛnələn]}}), sometimes spelled "epinephrin" or "adrenalin" respectively, is a [[hormone]]. It is a [[catecholamine]], a [[sympathomimetic]] monoamine derived from the [[amino acid]]s [[phenylalanine]] and [[tyrosine]]. The [[Latin]] roots ''ad-''+''renes'' and the [[Greek language|Greek]] roots ''epi-''+''nephros'' both literally mean "on/to the [[kidney]]" (referring to the [[adrenal gland]], which sits atop the kidneys and secretes epinephrine). Epinephrine is sometimes shortened to '''epi''' or to '''EP''' in medical [[jargon]].
  +
  +
==History==
  +
In May 1886, William Bates reported the discovery of a substance produced by the [[adrenal gland]] in the ''New York Medical Journal''. Epinephrine was isolated and identified in 1895 by Napoleon Cybulski, a Polish physiologist. The discovery was repeated in 1897 by John Jacob Abel.<ref>Aronson JK (2000). "[http://bmj.bmjjournals.com/cgi/content/full/320/7233/506 Where name and image meet]" - the argument for "adrenaline". ''British Medical Journal'' '''320''', 506-9.</ref>
  +
  +
Jokichi Takamine, a Japanese chemist, independently discovered the same hormone in 1900.<ref>{{cite journal |author=Yamashima T |title=Jokichi Takamine (1854-1922), the samurai chemist, and his work on adrenalin |journal=J Med Biogr |volume=11 |issue=2 |pages=95-102 |year=2003 |pmid=12717538}}</ref><ref>{{cite journal |author=Bennett M |title=One hundred years of adrenaline: the discovery of autoreceptors |journal=Clin Auton Res |volume=9 |issue=3 |pages=145-59 |year=1999 |pmid=10454061}}</ref>
  +
  +
It was first artificially synthesized in 1904 by Friedrich Stolz.
   
 
==Actions in the body==
 
==Actions in the body==
  +
{{Unreferencedsection|date=June 2007}}
Epinephrine plays a central role in the short-term [[Stress (medicine)|stress]] reaction&mdash;the physiological response to threatening or exciting conditions (see [[fight-or-flight response]]). It is secreted by the [[adrenal gland|adrenal medulla]]. When released into the bloodstream, epinephrine binds to multiple [[receptors]] and has numerous effects throughout the body. It increases [[heart rate]] and [[stroke volume]], dilates the [[pupil]]s, and constricts [[arterioles]] in the skin and gut while dilating arterioles in leg muscles. It elevates the blood sugar level by increasing [[hydrolysis]] of [[glycogen]] to [[glucose]] in the liver, and at the same time begins the breakdown of [[lipids]] in fat cells.
 
  +
  +
Epinephrine is a "[[fight or flight]]" hormone which is released from the adrenal glands when danger threatens. When secreted into the bloodstream, it rapidly prepares the body for action in emergency situations. The hormone boosts the supply of oxygen and glucose to the brain and muscles, while suppressing other non-emergency bodily processes (digestion in particular).
  +
 
Epinephrine plays a central role in the short-term [[Stress (medicine)|stress]] reaction&mdash;the physiological response to threatening, exciting, or environmental [[stressor]] conditions such as high [[noise health effects|noise]] levels or [[over-illumination|bright light]] (''see [[Fight-or-flight response]]''). It is secreted by the [[adrenal medulla]]. When released into the bloodstream, epinephrine binds to multiple [[adrenergic receptor|receptor]]s and has numerous effects throughout the body. It increases [[heart rate]] and [[stroke volume]], dilates the [[pupil]]s, and constricts [[arterioles]] in the skin and gut while dilating arterioles in leg muscles. It elevates the blood sugar level by increasing [[catalysis]] of [[glycogen]] to [[glucose]] in the liver, and at the same time begins the breakdown of [[lipid]]s in [[adipocyte|fat cells]]. Like some other stress hormones, epinephrine has a suppressive effect on the [[immune system]].
  +
 
Epinephrine is used as a [[medication|drug]] to treat [[cardiac arrest]] and other [[cardiac dysrhythmia]]s resulting in diminished or absent [[cardiac output]]; its action is to increase peripheral resistance via [[alpha adrenergic receptor|alpha-stimulated]] [[vasoconstriction]], so that blood is shunted to the body's core. This beneficial action comes with a significant negative consequence&mdash;increased cardiac irritability&mdash;which may lead to additional complications immediately following an otherwise successful resuscitation. Alternatives to this treatment include [[vasopressin]], a powerful [[antidiuretic]] which also increases peripheral vascular resistance leading to blood shunting via vasoconstriction, but without the attendant increase in myocardial irritability.
  +
  +
Because of its suppressive effect on the immune system, epinephrine is used to treat [[anaphylaxis]] and [[sepsis]]. Allergy patients undergoing [[immunotherapy]] may receive an epinephrine rinse before the allergen extract is administered, thus reducing the immune response to the administered allergen. It is also used as a [[bronchodilator]] for [[asthma]] if specific [[beta2-adrenergic receptor agonist|beta<sub>2</sub>-adrenergic receptor agonist]]s are unavailable or ineffective. Adverse reactions to epinephrine include [[palpitation]]s, [[tachycardia]], anxiety, headache, tremor, [[hypertension]], and acute [[pulmonary edema]].
  +
 
==Biosynthesis==
  +
[[Image:Biosynthese Adrenalin.png|thumb|500px|Epinephrine is synthesized from [[norepinephrine]] in a synthetic pathway shared by all catecholamines.]]
  +
  +
Epinephrine is synthesized from [[norepinephrine]] in a synthetic pathway shared by all catecholamines, including [[L-dopa]], [[dopamine]], [[norepinephrine]], and epinephrine.
  +
  +
Epinephrine is synthesized via methylation of the primary distal amine of [[norepinephrine]] by [[phenylethanolamine N-methyltransferase]] (PNMT) in the [[cytosol]] of [[adrenergic neuron]]s and cells of the [[adrenal medulla]] (so-called [[chromaffin cell]]s). PNMT is only found in the cytosol of cells of adrenal medullary cells. PNMT uses [[S-Adenosylmethionine|''S''-adenosylmethionine]] (SAMe) as a cofactor to donate the [[methyl]] group to norepinephrine, creating epinephrine.
  +
  +
For norepinephrine to be acted upon by PNMT in the cytosol, it must first be shipped out of [[chromaffin granule|granules]] of the chromaffin cells. This may occur via the catecholamine-H<sup>+</sup> exchanger [[VMAT1]]. VMAT1 is also responsible for transporting newly synthesized epinephrine from the cytosol back into chromaffin granules in preparation for release.
  +
  +
==Regulation==
  +
Epinephrine synthesis is solely under the control of the [[central nervous system]] (CNS). Several levels of regulation dominate epinephrine synthesis.
  +
  +
[[Adrenocorticotropic hormone]] (ACTH) and the [[sympathetic nervous system]] stimulate the synthesis of epinephrine precursors by enhancing the activity of enzymes involved in [[catecholamine]] synthesis. The specific enzymes are [[tyrosine hydroxylase]] in the synthesis of [[Levodopa|dopa]] and enzyme [[dopamine-β-hydroxylase]] in the synthesis of [[norepinephrine]].
  +
  +
ACTH also stimulates the [[adrenal cortex]] to release [[cortisol]], which increases the expression of PNMT in chromaffin cells, enhancing epinephrine synthesis.
  +
  +
The sympathetic nervous system, acting via [[splanchnic nerve]]s to the adrenal medulla, stimulates the release of epinephrine. [[Acetylcholine]] released by preganglionic sympathetic fibers of these nerves acts on [[nicotinic acetylcholine receptor]]s, causing cell depolarization and an influx of [[calcium]] through [[voltage-gated calcium channel]]s. Calcium triggers the exocytosis of chromaffin granules and thus the release of epinephrine (and norepinephrine) into the bloodstream.
   
  +
Unlike many other hormones, epinephrine (as with other catecholamines) does not exert any [[negative feedback]] to [[down-regulate]] its own synthesis.
Epinephrine is used as a [[medication|drug]] to promote peripheral vascular [[hemodynamics|resistance]] via alpha-stimulated [[vasoconstriction]] in [[cardiac arrest]] and other cardiac disrhythmias resulting in diminished or absent cardiac output, such that blood is shunted to the body's core. This beneficial action comes with a significant negative consequence, increased cardiac irritability, which may lead to additional complications immediately following an otherwise successful resuscitation. Alternatives to this treatment include [[vasopressin]], a powerful [[antidiuretic]] which also promotes peripheral vascular resistance leading to blood shunting via vasoconstriction, but without the attendant increase to myocardial irritability.
 
   
 
A [[pheochromocytoma]] is a tumor of the adrenal gland (or, rarely, the ganglia of the [[sympathetic nervous system]]), which results in the uncontrolled secretion of catecholamines, usually epinephrine.
Epinephrine is also used as a [[vasoconstrictor]] in [[anaphylaxis]] and [[sepsis]], and as a [[bronchodilator]] for [[asthma]] if specific [[beta-2-adrenergic agonist]]s are unavailable or ineffective. Allergy patients undergoing [[immunotherapy]] can get an epinephrine rinse before their allergen extract is administered. Adverse reactions to epinephrine include palpitations, [[tachycardia]], anxiety, headache, tremor, [[hypertension]], and acute [[pulmonary edema]].
 
   
  +
In liver cells, epinephrine binds to the β-Adrenergic receptor which changes conformation and helps Gs, a G protein, exchange GDP to GTP. This trimeric G protein dissociates to Gs alpha and Gs beta/gamma subunits. Ga alpha binds to adenyl cyclase thus converting ATP into Cyclic AMP. Cyclic AMP binds to the regulatory subunit of Protein Kinase A: Protein kinase A phosphorylates Phosphorylase Kinase. Meanwhile, Gs beta/gamma binds to the calcium channel channel and allows calcium ions to enter the cytoplasm. Calcium ions bind to calmodulin proteins, a protein present in all eukaryotic cells, which then binds to Phosphorylase Kinase and finishes its activation. Phosphorylase Kinase phosphorylates Phosphorylase which then phosphorylates glycogen and converts it to glucose-6-phosphate.
A [[pheochromocytoma]] is a tumor of the adrenal gland (or, rarely, the ganglia of the sympathetic nervous system), which secretes excessive amounts of [[catecholamine]]s, usually epinephrine.
 
   
 
==Pharmacology==
 
==Pharmacology==
  +
[[Image:G protein signal transduction (epinephrin pathway).png|thumb|400px|β-adrenergic receptors]]
Epinephrine's actions are mediated through [[adrenergic receptor]]s (sometimes referred to as adrenoceptors).
 
   
 
Epinephrine's actions are mediated through [[adrenergic receptor]]s:
It binds to α<sub>1</sub> receptors of liver cells, which activate inositol-phospholipid signaling pathway, signaling the phosphorylation of insulin, leading to reduced ability of insulin to bind to its receptors.
 
   
Epinephrine also activates β-adrenergic receptors of the liver and muscle cells, thereby activating the adenylate cyclase signaling pathway, which will in turn increase [[glycogenolysis]].
+
* It binds to ''α<sub>1</sub> receptors'' of [[liver]] cells, which activate [[inositol-phospholipid signaling pathway]], signaling the phosphorylation of [[insulin]], leading to reduced ability of insulin to bind to its receptors.
   
  +
* Epinephrine also activates ''β-adrenergic receptors'' of the liver and muscle cells, thereby activating the [[adenylate cyclase]] signaling pathway, which will in turn increase [[glycogenolysis]].
==Biosynthesis==
 
[[Image:adrenaline biosyn.png]]
 
   
  +
β<sub>2</sub> receptors are found primarily in [[skeletal muscle]] blood vessels where they trigger [[vasodilation]]. However, α-adrenergic receptors are found in most [[smooth muscle]]s and [[splanchnic]] vessels, and epinephrine triggers [[vasoconstriction]] in those vessels.
[[Image:adrenaline biosyn2.png]]
 
   
  +
Thus, depending on the patient, administration of epinephrine may ''raise'' or ''lower'' blood pressure, depending whether or not the net increase or decrease in peripheral resistance can balance the positive [[inotropic]] and [[chronotropic]] effects of epinephrine on the heart, effects which respectively increase the [[contractility]] and [[heart rate|rate]] of the heart.
==See also==
 
*[[EpiPen]]
 
*[[Anaphylaxis]]
 
*[[Adrenaline junkie]]
 
*[[Catechol-O-methyl transferase]]
 
   
 
==Terminology==
 
==Terminology==
Although widely referred to as "adrenaline" outside of the US, and the [[Laity|Lay public]] worldwide, the [[United_States_Approved_Name|USAN]] and [[International_Nonproprietary_Name|INN]] for this chemical is "epinephrine" because "adrenaline" bore too much similarity to the Parke, Davis & Co trademark "adrenelin" (without the "e") which was registered in the US.
+
Although widely referred to as ''adrenaline'' outside of the US, and the [[laity|lay public]] worldwide, the [[United States Approved Name|USAN]] and [[International Nonproprietary Name|INN]] for this chemical is ''epinephrine'' because ''adrenaline'' bore too much similarity to the Parke, Davis & Co trademark ''adrenalin'' (without the "e") which was registered in the US. The [[British Approved Name|BAN]] and [[European Pharmacopoeia|EP]] term for this chemical is ''adrenaline'', and is indeed now one of the few differences between the INN and BAN systems of names.
   
  +
Amongst US health professionals, the term ''epinephrine'' is used over ''adrenaline''. However, it should be noted that universally, pharmaceuticals that mimic the effects of epinephrine are called ''adrenergics'', and receptors for epinephrine are called ''adrenoceptors''.
The [[British_Approved_Name|BAN]] and [[European_Pharmacopoeia|EP]] term for this chemical is "adrenaline", and is indeed now one of the only differences between the INN and BAN systems of names.
 
  +
  +
== Isomers ==
  +
  +
Natural epinephrine is the ''(R)''-(−)-<small>L</small>-epinephrine [[stereoisomer]], see [[chirality (chemistry)|chirality]].
  +
  +
==Autoinjectors==
  +
Epinephrine is now also used in [[EpiPen]]s and [[Twinject]]s. [[EpiPen]]s are long narrow auto-injectors that administer epinephrine, [[Twinject]]s are similar but contain two doses of epinephrine.
  +
  +
Though both ''EpiPen'' and ''Twinject'' are trademark names, common usage of the terms are drifting toward the [[Genericized trademark|generic context]] of any epinephrine [[autoinjector]].
  +
 
==See also==
 
*[[Adrenaline rush]]
  +
*[[Adrenochrome]]
 
*[[Anaphylaxis]]
 
*[[Catechol-O-methyl transferase]]
  +
*[[Noise health effects]]
  +
*[[Vasoconstriction]]
  +
*[[Vasodilation]]
   
 
==References==
 
==References==
  +
<references/>
*Aronson JK (2000). "[http://bmj.bmjjournals.com/cgi/content/full/320/7233/506 Where name and image meet]" - the argument for "adrenaline". ''British Medical Journal'' '''320''', 506-9.
 
  +
*{{cite book | author = Walter F. Boron, Emile L. Boulpaep | title = Medical Physiology: A Cellular And Molecular Approach | publisher = Elsevier/Saunders | location = Philadelphia, PA| year = 2005 | id = ISBN 1-4160-2328-3}}
  +
  +
==External links==
  +
* {{McGrawHillAnimation|biochemistry|Epinephrine}}
   
 
{{Phenethylamines}}
 
{{Phenethylamines}}
{{Template:Hormones}}
 
   
 
{{Hormones}}
[[Category:Aromatic compounds]]
 
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{{Adrenergic and dopaminergic agents}}
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[[Category:Adrenergic drugs]]
 
[[Category:Bronchodilators]]
 
[[Category:Catecholamines]]
 
[[Category:Catecholamines]]
 
[[Category:Epinephrine]]
  +
[[Category:Heart rate effecting drugs]]
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[[Category:Hormones]]
 
[[Category:Neurotransmitters]]
 
[[Category:Neurotransmitters]]
[[Category:Neuroscience]]
 
[[Category:Bronchodilators]]
 
   
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<!--
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[[ar:أدرينالين]]
 
[[bg:Адреналин]]
 
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[[fr:Adrénaline]]
 
[[fr:Adrénaline]]
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[[hr:Adrenalin]]
 
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[[io:Adrenalino]]
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[[it:Adrenalina]]
 
[[he:אדרנלין]]
 
[[he:אדרנלין]]
 
[[lt:Adrenalinas]]
 
[[lt:Adrenalinas]]
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[[simple:Epinephrine]]
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[[sk:Epinefrín]]
 
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{{enWP| Epinephrine))
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{{enWP| Epinephrine}}

Latest revision as of 12:17, 1 January 2012

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Epinephrine chemical structure
Epinephrine

(R)-4-(1-hydroxy-
2-(methylamino)ethyl)benzene-1,2-diol
IUPAC name
CAS number
51-43-4
ATC code

A01AD01 . . . . .

PubChem
838
DrugBank
APRD00450
Chemical formula {{{chemical_formula}}}
Molecular weight 183.204 g/mol
Bioavailability Nil (oral)
Metabolism adrenergic synapse (MAO and COMT)
Elimination half-life 2 minutes
Excretion n/a
Pregnancy category {{{pregnancy_category}}}
Legal status {{{legal_status}}}
Routes of administration IV, IM, endotracheal


Adrenaline redirects here

Epinephrine (INN) (IPA: [ˌɛpɪˈnɛfrən]) or adrenaline (European Pharmacopoeia and British Approved Name|BAN) (IPA: [əˈdrɛnələn]), sometimes spelled "epinephrin" or "adrenalin" respectively, is a hormone. It is a catecholamine, a sympathomimetic monoamine derived from the amino acids phenylalanine and tyrosine. The Latin roots ad-+renes and the Greek roots epi-+nephros both literally mean "on/to the kidney" (referring to the adrenal gland, which sits atop the kidneys and secretes epinephrine). Epinephrine is sometimes shortened to epi or to EP in medical jargon.

History

In May 1886, William Bates reported the discovery of a substance produced by the adrenal gland in the New York Medical Journal. Epinephrine was isolated and identified in 1895 by Napoleon Cybulski, a Polish physiologist. The discovery was repeated in 1897 by John Jacob Abel.[1]

Jokichi Takamine, a Japanese chemist, independently discovered the same hormone in 1900.[2][3]

It was first artificially synthesized in 1904 by Friedrich Stolz.

Actions in the body

Epinephrine is a "fight or flight" hormone which is released from the adrenal glands when danger threatens. When secreted into the bloodstream, it rapidly prepares the body for action in emergency situations. The hormone boosts the supply of oxygen and glucose to the brain and muscles, while suppressing other non-emergency bodily processes (digestion in particular).

Epinephrine plays a central role in the short-term stress reaction—the physiological response to threatening, exciting, or environmental stressor conditions such as high noise levels or bright light (see Fight-or-flight response). It is secreted by the adrenal medulla. When released into the bloodstream, epinephrine binds to multiple receptors and has numerous effects throughout the body. It increases heart rate and stroke volume, dilates the pupils, and constricts arterioles in the skin and gut while dilating arterioles in leg muscles. It elevates the blood sugar level by increasing catalysis of glycogen to glucose in the liver, and at the same time begins the breakdown of lipids in fat cells. Like some other stress hormones, epinephrine has a suppressive effect on the immune system.

Epinephrine is used as a drug to treat cardiac arrest and other cardiac dysrhythmias resulting in diminished or absent cardiac output; its action is to increase peripheral resistance via alpha-stimulated vasoconstriction, so that blood is shunted to the body's core. This beneficial action comes with a significant negative consequence—increased cardiac irritability—which may lead to additional complications immediately following an otherwise successful resuscitation. Alternatives to this treatment include vasopressin, a powerful antidiuretic which also increases peripheral vascular resistance leading to blood shunting via vasoconstriction, but without the attendant increase in myocardial irritability.

Because of its suppressive effect on the immune system, epinephrine is used to treat anaphylaxis and sepsis. Allergy patients undergoing immunotherapy may receive an epinephrine rinse before the allergen extract is administered, thus reducing the immune response to the administered allergen. It is also used as a bronchodilator for asthma if specific beta2-adrenergic receptor agonists are unavailable or ineffective. Adverse reactions to epinephrine include palpitations, tachycardia, anxiety, headache, tremor, hypertension, and acute pulmonary edema.

Biosynthesis

Biosynthese Adrenalin

Epinephrine is synthesized from norepinephrine in a synthetic pathway shared by all catecholamines.

Epinephrine is synthesized from norepinephrine in a synthetic pathway shared by all catecholamines, including L-dopa, dopamine, norepinephrine, and epinephrine.

Epinephrine is synthesized via methylation of the primary distal amine of norepinephrine by phenylethanolamine N-methyltransferase (PNMT) in the cytosol of adrenergic neurons and cells of the adrenal medulla (so-called chromaffin cells). PNMT is only found in the cytosol of cells of adrenal medullary cells. PNMT uses S-adenosylmethionine (SAMe) as a cofactor to donate the methyl group to norepinephrine, creating epinephrine.

For norepinephrine to be acted upon by PNMT in the cytosol, it must first be shipped out of granules of the chromaffin cells. This may occur via the catecholamine-H+ exchanger VMAT1. VMAT1 is also responsible for transporting newly synthesized epinephrine from the cytosol back into chromaffin granules in preparation for release.

Regulation

Epinephrine synthesis is solely under the control of the central nervous system (CNS). Several levels of regulation dominate epinephrine synthesis.

Adrenocorticotropic hormone (ACTH) and the sympathetic nervous system stimulate the synthesis of epinephrine precursors by enhancing the activity of enzymes involved in catecholamine synthesis. The specific enzymes are tyrosine hydroxylase in the synthesis of dopa and enzyme dopamine-β-hydroxylase in the synthesis of norepinephrine.

ACTH also stimulates the adrenal cortex to release cortisol, which increases the expression of PNMT in chromaffin cells, enhancing epinephrine synthesis.

The sympathetic nervous system, acting via splanchnic nerves to the adrenal medulla, stimulates the release of epinephrine. Acetylcholine released by preganglionic sympathetic fibers of these nerves acts on nicotinic acetylcholine receptors, causing cell depolarization and an influx of calcium through voltage-gated calcium channels. Calcium triggers the exocytosis of chromaffin granules and thus the release of epinephrine (and norepinephrine) into the bloodstream.

Unlike many other hormones, epinephrine (as with other catecholamines) does not exert any negative feedback to down-regulate its own synthesis.

A pheochromocytoma is a tumor of the adrenal gland (or, rarely, the ganglia of the sympathetic nervous system), which results in the uncontrolled secretion of catecholamines, usually epinephrine.

In liver cells, epinephrine binds to the β-Adrenergic receptor which changes conformation and helps Gs, a G protein, exchange GDP to GTP. This trimeric G protein dissociates to Gs alpha and Gs beta/gamma subunits. Ga alpha binds to adenyl cyclase thus converting ATP into Cyclic AMP. Cyclic AMP binds to the regulatory subunit of Protein Kinase A: Protein kinase A phosphorylates Phosphorylase Kinase. Meanwhile, Gs beta/gamma binds to the calcium channel channel and allows calcium ions to enter the cytoplasm. Calcium ions bind to calmodulin proteins, a protein present in all eukaryotic cells, which then binds to Phosphorylase Kinase and finishes its activation. Phosphorylase Kinase phosphorylates Phosphorylase which then phosphorylates glycogen and converts it to glucose-6-phosphate.

Pharmacology

G protein signal transduction (epinephrin pathway)

β-adrenergic receptors

Epinephrine's actions are mediated through adrenergic receptors:

  • It binds to α1 receptors of liver cells, which activate inositol-phospholipid signaling pathway, signaling the phosphorylation of insulin, leading to reduced ability of insulin to bind to its receptors.
  • Epinephrine also activates β-adrenergic receptors of the liver and muscle cells, thereby activating the adenylate cyclase signaling pathway, which will in turn increase glycogenolysis.

β2 receptors are found primarily in skeletal muscle blood vessels where they trigger vasodilation. However, α-adrenergic receptors are found in most smooth muscles and splanchnic vessels, and epinephrine triggers vasoconstriction in those vessels.

Thus, depending on the patient, administration of epinephrine may raise or lower blood pressure, depending whether or not the net increase or decrease in peripheral resistance can balance the positive inotropic and chronotropic effects of epinephrine on the heart, effects which respectively increase the contractility and rate of the heart.

Terminology

Although widely referred to as adrenaline outside of the US, and the lay public worldwide, the USAN and INN for this chemical is epinephrine because adrenaline bore too much similarity to the Parke, Davis & Co trademark adrenalin (without the "e") which was registered in the US. The BAN and EP term for this chemical is adrenaline, and is indeed now one of the few differences between the INN and BAN systems of names.

Amongst US health professionals, the term epinephrine is used over adrenaline. However, it should be noted that universally, pharmaceuticals that mimic the effects of epinephrine are called adrenergics, and receptors for epinephrine are called adrenoceptors.

Isomers

Natural epinephrine is the (R)-(−)-L-epinephrine stereoisomer, see chirality.

Autoinjectors

Epinephrine is now also used in EpiPens and Twinjects. EpiPens are long narrow auto-injectors that administer epinephrine, Twinjects are similar but contain two doses of epinephrine.

Though both EpiPen and Twinject are trademark names, common usage of the terms are drifting toward the generic context of any epinephrine autoinjector.

See also

References

  1. Aronson JK (2000). "Where name and image meet" - the argument for "adrenaline". British Medical Journal 320, 506-9.
  2. Yamashima T (2003). Jokichi Takamine (1854-1922), the samurai chemist, and his work on adrenalin. J Med Biogr 11 (2): 95-102.
  3. Bennett M (1999). One hundred years of adrenaline: the discovery of autoreceptors. Clin Auton Res 9 (3): 145-59.
  • Walter F. Boron, Emile L. Boulpaep (2005). Medical Physiology: A Cellular And Molecular Approach, Philadelphia, PA: Elsevier/Saunders. ISBN 1-4160-2328-3.

External links


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Target-derived NGF, BDNF, NT-3

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