Adrenalin

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Biography

Epinephrine (also known as adrenaline ) is a hormone and a neurotransmitter . Epinephrine has many functions in the body, regulating heart rate , blood vessel and air passage diameters, and metabolic shifts; epinephrine release is a crucial component of the fight-or-flight response of the sympathetic nervous system . In chemical terms, epinephrine is one of a group of monoamine s called the catecholamine s. It is produced in some neuron s of the central nervous system, and in the Medullary chromaffin cell|chromaffin cell s of the adrenal medulla from the amino acid s phenylalanine and tyrosine .

Terminology

This chemical is widely referred to as "adrenaline" outside the United States; however, its United States Adopted Name and International Nonproprietary Name is epinephrine. Epinephrine was chosen as the generic name in the United States because John Jacob Abel|John Abel , who prepared extracts from the adrenal glands in 1897, used that name for his extracts. In 1901, Jokichi Takamine patented a purified adrenal extract, and called it "adrenalin", which was List of generic and genericized trademarks|trademark ed by Parke-Davis|Parke, Davis & Co in the US. In the belief that Abel's extract was the same as Takamine's, a belief since disputed, epinepherine became the generic name in the US. The British Approved Name and European Pharmacopoeia term for this chemical is adrenaline and is indeed now one of the few differences between the INN and BAN systems of names., Medicines and Healthcare products Regulatory Agency

Among American health professionals and scientists, the term epinephrine is used over adrenaline . However, pharmaceuticals that mimic the effects of epinephrine are often called adrenergics, and receptors for epinephrine are called adrenergic receptors or adrenoceptors.

Discovery

Extracts of the adrenal gland were first obtained by Polish physiologist Napoleon Cybulski in 1895. These extracts, which he called nadnerczyna , contained adrenaline and other catecholamines. Japanese chemist Jokichi Takamine and his assistant Keizo Uenaka independently discovered adrenaline in 1900. In 1901, Takamine successfully isolated and purified the hormone from the adrenal glands of sheep and oxen. Adrenaline was first synthesized in the laboratory by Friedrich Stolz and Henry Drysdale Dakin , independently, in 1904.

Mechanism of action

Organ	Effects
Heart	Increases heart rate
Lung s	Increases respiratory rate
Nearly all tissues	Vasoconstriction or vasodilation
Liver	Stimulates glycogenolysis
N/ A, systemic	Triggers lipolysis
N/ A, systemic	Muscle contraction

As a hormone and neurotransmitter, adrenaline acts on nearly all body tissues. Its actions vary by tissue type and tissue expression of adrenergic receptor s. For example, high levels of adrenaline causes smooth muscle relaxation in the airways but causes contraction of the smooth muscle that lines most arteriole s.

Adrenaline acts by binding to a variety of adrenergic receptor s. Adrenaline is a nonselective agonist of all adrenergic receptors, including the major subtypes Alpha-1 adrenergic receptor|a₁ , Alpha-2 adrenergic receptor|a₂ , Beta-1 adrenergic receptor|ß₁ , Beta-2 adrenergic receptor|ß₂ , and Beta-3 adrenergic receptor|ß₃ . Epinephrine's binding to these receptors triggers a number of metabolic changes. Binding to a-adrenergic receptors inhibits insulin secretion by the pancreas , stimulates glycogenolysis in the liver and muscle , and stimulates glycolysis in muscle. ß-Adrenergic receptor binding triggers glucagon secretion in the pancreas, increased adrenocorticotropic hormone (ACTH) secretion by the pituitary gland , and increased lipolysis by adipose tissue . Together, these effects lead to increased blood glucose and fatty acid s, providing substrates for energy production within cells throughout the body.

Medical uses

Adrenaline is used to treat a number of conditions including: cardiac arrest , anaphylaxis , and superficial bleeding. It has been used historically for bronchospasm and hypoglycemia , but newer treatments for these, such as salbutamol , a synthetic epinephrine derivative, and dextrose , respectively, are currently preferred.

Cardiac arrest

Adrenaline is used as a medication|drug to treat cardiac arrest and other cardiac dysrhythmia s resulting in diminished or absent cardiac output . Its actions are to increase peripheral resistance via Alpha-1 adrenergic receptor|a₁receptor -dependent vasoconstriction and to increase cardiac output via its binding to ß₁ receptors.

Anaphylaxis

Due to its Vasoconstriction|vasoconstrictive effects, adrenaline is the drug of choice for treating anaphylaxis . Protein allergy|Allergy patients undergoing immunotherapy may receive an adrenaline 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 ß₂ agonists are unavailable or ineffective.

Because of various expressions of a₁ or ß₂ receptors, depending on the patient, administration of adrenaline may raise or lower blood pressure, depending on whether or not the net increase or decrease in peripheral resistance can balance the positive inotropic and chronotropic effects of adrenaline on the heart, effects that increase the contractility and heart rate|rate , respectively, of the heart.
The usual concentration for SQ or IM injection is 0.3 - 0.5& nbsp;mg 1:1,000.

Croup

Racemic epinephrine has historically been used for the Croup#Treatment|treatment of croup . Racemic adrenaline is a 1:1 mixture of the dextrorotatory (d) and levorotatory (l) isomer s of adrenaline. The l- form is the active component. Racemic adrenaline works by stimulation of the a-adrenergic receptors in the airway, with resultant mucosal vasoconstriction and decreased subglottic edema, and by stimulation of the ß-adrenergic receptors, with resultant relaxation of the bronchial smooth muscle.

In local anesthetics

Adrenaline is added to injectable forms of a number of local anesthetics, such as bupivacaine and lidocaine , as a vasoconstrictor to slow the absorption and, therefore, prolong the action of the anesthetic agent. Some of the adverse effects of local anesthetic use, such as apprehension, tachycardia, and tremor, may be caused by adrenaline.R. Rahn and B. Ball. Local Anesthesia in Dentistry , 3M ESPE AG, ESPE Platz, Seefeld, Germany, 2001, 44 pp.

Autoinjectors

Adrenaline is available in an autoinjector delivery system. EpiPen s, Anapen s, and Twinject s all use adrenaline as their active ingredient. Twinjects contain a second dose of adrenaline in a separate syringe and needle delivery system contained within the body of the autoinjector.

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

Adverse effects

Adverse reactions to adrenaline include palpitation s, tachycardia , arrhythmia , anxiety , headache , tremor , hypertension , and acute pulmonary edema . - "The Definition of Epinephrine"

Use is contraindicated in people on nonselective beta blocker|ß-blockers , because severe hypertension and even cerebral hemorrhage may result. Although commonly believed that administration of adrenaline may cause heart failure by constricting coronary arteries, this is not the case. Coronary arteries have only ß₂ receptors, which cause vasodilation in the presence of adrenaline. Even so, administering high-dose adrenaline has not been definitively proven to improve survival or neurologic outcomes in adult victims of cardiac arrest.

Measurement in biological fluids

Adrenaline may be quantified in blood, plasma, or serum as a diagnostic aid, to monitor therapeutic administration, or to identify the causative agent in a potential poisoning victim. Endogenous plasma adrenaline concentrations in resting adults are normally less than 10& nbsp;ng/L, but may increase by 10-fold during exercise and by 50-fold or more during times of stress. Pheochromocytoma patients often have plasma adrenaline levels of 1000-10,000& nbsp;ng/L. Parenteral administration of adrenaline to acute-care cardiac patients can produce plasma concentrations of 10,000 to 100,000& nbsp;ng/L.

Biosynthesis and regulation

Adrenaline is synthesized in the medulla of the adrenal gland in an enzymatic pathway that converts the amino acid tyrosine into a series of intermediates and, ultimately, adrenaline. Tyrosine is first oxidized to L-DOPA , which is subsequently decarboxylated to give dopamine . Oxidation gives norepinephrine , which is methylated to give epinephrine.

Adrenaline is synthesized via methylation of the primary distal amine of noradrenaline 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 found in the cytosol of only cells of adrenal medullary cells. PNMT uses S-adenosylmethionine (SAMe) as a cofactor to donate the methyl group to noradrenaline, creating adrenaline.

For noradrenaline 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⁺ exchanger VMAT1 . VMAT1 is also responsible for transporting newly synthesized adrenaline from the cytosol back into chromaffin granules in preparation for release.
In liver cells, adrenaline binds to the ß-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. Gs 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 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 glycogen phosphorylase , which then phosphorylates glycogen and converts it to glucose-6-phosphate.

Regulation

The major physiologic triggers of adrenaline release center upon stress (medicine)|stresses , such as physical threat, excitement, noise, bright lights, and high ambient temperature. All of these stimuli are processed in the central nervous system .

Adrenocorticotropic hormone (ACTH) and the sympathetic nervous system stimulate the synthesis of adrenaline precursors by enhancing the activity of tyrosine hydroxylase and dopamine-ß-hydroxylase , two key enzymes involved in catecholamine synthesis. ACTH also stimulates the adrenal cortex to release cortisol , which increases the expression of PNMT in chromaffin cells, enhancing adrenaline synthesis. This is most often done in response to stress. The sympathetic nervous system, acting via splanchnic nerve s to the adrenal medulla, stimulates the release of adrenaline. 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 adrenaline (and noradrenaline) into the bloodstream.
Adrenaline (as with noradrenaline) does exert negative feedback to down-regulate its own synthesis at the presynaptic alpha-2 adrenergic receptor. Abnormally elevated levels of adrenaline can occur in a variety of conditions, such as surreptitious epinephrine administration, pheochromocytoma , and other tumors of the sympathetic ganglia .

Its action is terminated with reuptake into nerve terminal endings, some minute dilution, and metabolism by monoamine oxidase and catechol-O-methyl transferase .

Chemical synthesis

Epinephrine may be synthesized by the reaction of catechol ( 1 ) with chloroacetyl chloride ( 2 ), followed by the reaction with methylamine to give the ketone ( 4 ), which is reduced to the desired hydroxy compound ( 5 ). The racemic mixture may be chiral resolution|separated using tartaric acid .

For isolation from the adrenal glands tissue of livestock:

J. Takamine, J. Soc. Chem. Ind. , 20, 746 (1901).

J. B. Aldrich, Am. J. Physiol. , 5, 457 (1901).

Synthetic production:

A. F. Stolz, Chem. Ber. , 37, 4149 (1904).

K. R. Payne, Ind. Chem. Chem. Manuf. , 37, 523 (1961).

H. Loewe, Arzneimittel-Forsch. , 4, 583 (1954).

Farbenwerke Meister Lucins & Bruning in Hochst a.M., (1903).

Farbenwerke Meister Lucins & Bruning in Hochst a.M., (1908).

D. Flacher, Z. Physiol. Chem. , 58, 189 (1908).

Adrenaline junkie

Adrenaline junkie is a non-medical colloquial term used to describe somebody appearing to be addicted to Endogeny|endogenous epinephrine. The "high" is caused by self-inducing a fight-or-flight response by intentionally engaging in stressful or risky behavior, which causes a release of epinephrine by the adrenal gland. The term adrenaline junkie was popularly used in the 1991 movie Point Break to describe individuals enjoying dangerous activities (such as extreme sport s, e.g. BASE jumping ) for the adrenaline "rush". Adrenaline junkies appear to favor stressful activities for the release of epinephrine as a stress response. Whether or not the positive response is caused specifically by epinephrine is difficult to determine, as endorphin s are also released during the fight-or-flight response to such activities. by Elizabeth Scott, M.S. (updated: November 1, 2007) About.com Health's Disease and Condition content is reviewed by the Medical Review Board. - Explanations - Brain -ChangingMinds.org.

Notes

Copyright Citations

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