Information about Adrenergic Receptor
The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines. Adrenergic receptors specifically bind their endogenous ligands, the catecholamines adrenaline and noradrenaline (called epinephrine and norepinephrine in the USA), and are activated by these.
Many cells possess these receptors, and the binding of an agonist will generally cause a sympathetic response (ie the fight-or-flight response). For instance, the heart rate will increase and the pupils will dilate, energy will be mobilized, and blood flow diverted from other organs to skeletal muscle.(Note: Sympathetic activity will result in vasodilation of coronary arteries via the Beta-2 adrenergic receptors.)
The absence of "ADRA1C" is intentional. At one time, there was a subtype known as C, but was found to be one of the previously discovered subtypes. To avoid confusion, it was decided that there would never be a C subtype again and so if any new subtypes were discovered, naming would start with D.
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In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates
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Many cells possess these receptors, and the binding of an agonist will generally cause a sympathetic response (ie the fight-or-flight response). For instance, the heart rate will increase and the pupils will dilate, energy will be mobilized, and blood flow diverted from other organs to skeletal muscle.(Note: Sympathetic activity will result in vasodilation of coronary arteries via the Beta-2 adrenergic receptors.)
Subtypes of adrenergic receptors
There are several types of adrenergic receptors, but there are two main groups: α-Adrenergic and β-Adrenergic.- α receptors bind norepinephrine and epinephrine, though norepinephrine has higher affinity. Phenylephrine is a selective agonist of the α receptor.
- β receptors are linked to Gs proteins, which in turn are linked to adenylyl cyclase. Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP. Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding.
Comparison
| Receptor type | Agonist potency order | Location / Action | Mechanism | Agonists | Antagonists |
| α1: ADRA1A, ADRA1B, ADRA1D | noradrenaline≥ adrenaline >> isoprenaline | Smooth muscle. In blood vessels the principal effect is vasoconstriction. Blood vessels with α1 receptors are present in the skin and the gastrointestinal system, and during the fight-or-flight response vasoconstriction results in the decreased blood flow to these organs. This accounts for an individual's skin appearing pale when frightened. In the GI tract, the effect is relaxation. | Gq: phospholipase C (PLC) activated, IP3 and calcium up | noradrenaline phenylephrine methoxamine Cirazoline | (Alpha blockers) phenoxybenzamine phentolamine prazosin tamsulosin terazosin |
| α2: ADRA2A, ADRA2B, ADRA2C | adrenaline > noradrenaline >> isoprenaline | Pre- and postsynaptic nerve terminals. Mediates synaptic transmission. | Gi: adenylate cyclase inactivated, cAMP down | clonidine lofexidine xylazine Tizanidine Guanfacine | (Alpha blockers) yohimbine rauwolscine idazoxan |
| β1: ADRB1 | isoprenaline > noradrenaline > adrenaline | Heart and cerebral cortex. In heart, agonists enhance myocardial contractility and increase heart rate. Also found on juxtaglomerular cells, activation results in renin release. | Gs: adenylate cyclase activated, cAMP up | noradrenaline isoprenaline dobutamine | (Beta blockers) metoprolol atenolol |
| β2: ADRB2 | isoprenaline > adrenaline > noradrenaline | Lung, smooth muscle, cerebellum, skeletal muscle. In lung, agonists cause bronchiole dilation. Agonists can be useful in treating asthma. In smooth muscle, relaxes walls. Relaxes uterine muscle and promotes release of insulin. | Gs: adenylate cyclase activated, cAMP up | (Short/long) salbutamol (albuterol in USA) bitolterol mesylate formoterol isoproterenol levalbuterol metaproterenol salmeterol terbutaline | (Beta blockers) butoxamine propranolol ritodrine |
| β3: ADRB3 | isoprenaline > noradrenaline = adrenaline | Adipose tissue. Agonists enhance lipolysis. | Gs: adenylate cyclase activated, cAMP up | L-796568 CL 316,243 LY 368842 Ro 40-2148 | (Beta blockers) SR 59230A |
The absence of "ADRA1C" is intentional. At one time, there was a subtype known as C, but was found to be one of the previously discovered subtypes. To avoid confusion, it was decided that there would never be a C subtype again and so if any new subtypes were discovered, naming would start with D.
Diagrams
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Labels in German, but most ideas can be understood. "Glatter" = "smooth", "hemmung" = "inhibition", "herzmuskels" = "heart muscle".
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Epinephrine binds its receptor, that associates with an heterotrimeric G protein. The G protein associates with adenylate cyclase that converts ATP to cAMP, spreading the signal (more details...)
See also
References
- Rang HP, Dale MM, Ritter JM, Moore PK (2003). "Ch. 11", Pharmacology. Elsevier Churchill Livingstone. ISBN 0-443-07145-4.
- Rang HP, Dale MM, Ritter JM, Flower RJ (2007). "Ch. 11", Rang and Dale's Pharmacology. Elsevier Churchill Livingstone, 169-170. ISBN 0-443-06911-5.
External links
- The Adrenergic Receptors
- IUPHAR GPCR Database - Adrenoceptors
- Basic Neurochemistry: α- and β-Adrenergic Receptors
- Brief overview of functions of the beta-3 receptor
- Theory of receptor activation
- Desensitization of beta-1-receptors
Adrenergic agonists | |
|---|---|
| Direct Acting | Albuterol Clonidine Dobutamine Dopamine Epinephrine Formoterol Isoproterenol Metaproterenol Methoxamine Norepinephrine - Phenylephrine Piruterol Salmeterol Tamsulosin Terbutaline |
| Indirect Acting | Amphetamine Tyramine |
| Mixed Action | Ephedrine |
G protein-coupled receptors (GPCRs), also known as seven transmembrane receptors, 7TM receptors, heptahelical receptors, and G protein linked receptors (GPLR
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Catecholamines are chemical compounds derived from the amino acid tyrosine containing catechol and amine groups. Some of them are biogenic amines. Catecholamines are water soluble and are 50% bound to plasma proteins, so they circulate in the bloodstream.
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For other uses, see Receptor.
In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates
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The word endogenous means "arising from within", the opposite of exogenous.
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Biology
Endogenous substances are those that originate from within an organism, tissue, or cell [1] ...... Click the link for more information.
In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as
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Epinephrine (INN) (IPA: [ˌɛpɪˈnɛfrən]) or adrenaline (European Pharmacopoeia and BAN) (IPA: [əˈdrɛnələn]
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Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. The natural stereoisomer is L -(−)-(R)-norepinephrine.
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Epinephrine (INN) (IPA: [ˌɛpɪˈnɛfrən]) or adrenaline (European Pharmacopoeia and BAN) (IPA: [əˈdrɛnələn]
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Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. The natural stereoisomer is L -(−)-(R)-norepinephrine.
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Motto
"In God We Trust" (since 1956)
"E Pluribus Unum" ("From Many, One"; Latin, traditional)
Anthem
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"In God We Trust" (since 1956)
"E Pluribus Unum" ("From Many, One"; Latin, traditional)
Anthem
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agonist is a substance that binds to a specific receptor and triggers a response in the cell. It mimics the action of an endogenous ligand (such as hormone or neurotransmitter) that binds to the same receptor.
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The fight-or-flight response, also called hyperarousal or the acute stress response, was first described by Walter Cannon in 1915[1][2].
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Heart rate is a term used to describe the frequency of the cardiac cycle. It is considered one of the four vital signs. Usually it is calculated as the number of contractions (heart beats) of the heart in one minute and expressed as "beats per minute" (bpm).
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The pupil (Latin pupilla "little doll" > pupa "doll") is the variable-sized, black circular or slit shaped opening in the center of the iris that regulates the amount of light that enters the eye.
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Skeletal muscle is a type of striated muscle, usually attached to the skeleton. Skeletal muscles are used to create movement, by applying force to bones and joints; via contraction.
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A vasodilator is a drug or chemical that relaxes the smooth muscle in blood vessels, which causes them to dilate. Dilation of arterial blood vessels (mainly arterioles) lead to a decrease in blood pressure.
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Phenylephrine or Neo-Synephrine is an α-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil and to increase blood pressure. Phenylephrine has recently been marketed as a substitute for pseudoephedrine, (e.g.
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G proteins, short for guanine nucleotide binding proteins, are a family of proteins involved in second messenger cascades. Their nomenclature originates from their ability to function as "molecular switches", alternating between an inactive guanosine diphosphate (GDP) and
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Adenylate cyclase (EC 4.6.1.1 , also known as adenylyl cyclase or AC) is a lyase enzyme.
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Types
There are nine known adenylate cyclases in mammals:- ADCY1
- ADCY2
- ADCY3
- ADCY4
- ADCY5
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Cyclic adenosine monophosphate (cAMP, cyclic AMP or 3'-5'-cyclic adenosine monophosphate) is a molecule that is important in many biological processes; it is derived from adenosine triphosphate (ATP).
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In cell biology, cAMP-dependent protein kinase (cAPK), also known as protein kinase A (PKA, EC 2.7.11.11 ), refers to a family of enzymes whose activity is dependent on the level of cyclic AMP (cAMP) in the cell.
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In cell physiology, a secondary messenger system (also known as a second messenger system) is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change.
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An adrenergic is a drug, or other substance, which has effects similar to, or the same as, epinephrine (adrenaline). Alternatively, it may refer to something which is susceptible to epinephrine, or similar substances, such as a biological receptor (specifically, the adrenergic
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An Adrenergic antagonist is a pharmaceutical substance that acts to inhibit the action of the adrenergic receptors.
It has the opposite effect as adrenergic agonists.
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It has the opposite effect as adrenergic agonists.
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Isoproterenol hydrochloride or isoprenaline (Medihaler-Iso®) is a sympathomimetic beta adrenergic receptor agonist medication.
It is structurally similar to epinephrine but acts for the most part on beta receptors.
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It is structurally similar to epinephrine but acts for the most part on beta receptors.
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Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs and elsewhere like the bladder and abdominal cavity, the uterus, male and female reproductive tracts, the gastrointestinal tract, the respiratory tract, the vasculature, the skin and the
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The blood vessels are part of the cardiovascular system and function to transport blood throughout the body. The most important types, arteries and veins, carry blood away from or towards the heart, respectively.
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Vasoconstriction is a narrowing of the lumen of blood vessels.
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Factors
Factors that trigger vasoconstriction are both of exogenous origin, i.e. medication, and as a response from the body itself.Body mechanisms
Vasoconstriction is a procedure of the body to e.g...... Click the link for more information.
Skin layers: epidermis, dermis, and subcutis, showing a hair follicle, sweat gland & sebaceous gland.]] In zootomy and dermatology, skin is the largest organ of the integumentary system made up of multiple layers of epithelial tissues that guard underlying muscles and organs.
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gastrointestinal tract (GI tract), also called the digestive tract, or the alimentary canal, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
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