The adrenergic receptors or adrenoceptors are a class of
G protein-coupled receptors that are targets of many
catecholamine
A catecholamine (; abbreviated CA) is a monoamine neurotransmitter, an organic compound that has a catechol (benzene with two hydroxyl side groups next to each other) and a side-chain amine.
Catechol can be either a free molecule or a substi ...
s like
norepinephrine (noradrenaline) and
epinephrine
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
(adrenaline) produced by the body, but also many medications like
beta blocker
Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack (secondary prevention). They are al ...
s,
beta-2 (β2) agonists and
alpha-2 (α2) agonists, which are used to treat
high blood pressure and
asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, for example.
Many cells have these receptors, and the binding of a catecholamine to the receptor will generally stimulate the
sympathetic nervous system (SNS). The SNS is responsible for the
fight-or-flight response, which is triggered by experiences such as
exercise or
fear-causing situations. This response
dilates pupils, increases heart rate, mobilizes energy, and diverts blood flow from non-essential organs to
skeletal muscle. These effects together tend to increase physical performance momentarily.
History
By the turn of the 19th century, it was agreed that the stimulation of sympathetic nerves could cause different effects on body tissues, depending on the conditions of stimulation (such as the presence or absence of some toxin). Over the first half of the 20th century, two main proposals were made to explain this phenomenon:
# There were (at least) two different types of neurotransmitters released from sympathetic nerve terminals, or
# There were (at least) two different types of detector mechanisms for a single neurotransmitter.
The first hypothesis was championed by
Walter Bradford Cannon
Walter Bradford Cannon (October 19, 1871 – October 1, 1945) was an American physiologist, professor and chairman of the Department of Physiology at Harvard Medical School. He coined the term " fight or flight response", and developed the theory ...
and
Arturo Rosenblueth
Arturo Rosenblueth Stearns (October 2, 1900 – September 20, 1970) was a Mexican researcher, physician and physiologist, who is known as one of the pioneers of cybernetics.
Biography
Rosenblueth was born in 1900 in Ciudad Guerrero, Chihuahua ...
, who interpreted many experiments to then propose that there were two neurotransmitter substances, which they called sympathin E (for 'excitation') and sympathin I (for 'inhibition').
The second hypothesis found support from 1906 to 1913, when
Henry Hallett Dale
Sir Henry Hallett Dale (9 June 1875 – 23 July 1968) was an English pharmacologist and physiologist. For his study of acetylcholine as agent in the chemical transmission of nerve pulses (neurotransmission) he shared the 1936 Nobel Prize in Ph ...
explored the effects of adrenaline (which he called adrenine at the time), injected into animals, on blood pressure. Usually, adrenaline would increase the blood pressure of these animals. Although, if the animal had been exposed to
ergotoxine, the blood pressure decreased. He proposed that the ergotoxine caused "selective paralysis of motor myoneural junctions" (i.e. those tending to increase the blood pressure) hence revealing that under normal conditions that there was a "mixed response", including a mechanism that would relax smooth muscle and cause a fall in blood pressure. This "mixed response", with the same compound causing either contraction or relaxation, was conceived of as the response of different types of junctions to the same compound.
This line of experiments were developed by several groups, including DT Marsh and colleagues, who in February 1948 showed that a series of compounds structurally related to adrenaline could also show either contracting or relaxing effects, depending on whether or not other toxins were present. This again supported the argument that the muscles had two different mechanisms by which they could respond to the same compound. In June of that year,
Raymond Ahlquist
Raymond Perry Ahlquist (July 26, 1914 – April 15, 1983) was an American pharmacist and pharmacologist. He published seminal work in 1948 that divided adrenoceptors into α- and β-adrenoceptor subtypes. This discovery explained the acti ...
, Professor of Pharmacology at Medical College of Georgia, published a paper concerning adrenergic nervous transmission. In it, he explicitly named the different responses as due to what he called α receptors and β receptors, and that the only sympathetic transmitter was adrenaline. While the latter conclusion was subsequently shown to be incorrect (it is now known to be noradrenaline), his receptor nomenclature and concept of ''two different types of detector mechanisms for a single neurotransmitter'', remains. In 1954, he was able to incorporate his findings in a textbook, ''Drill's Pharmacology in Medicine'', and thereby promulgate the role played by α and β receptor sites in the adrenaline/noradrenaline cellular mechanism. These concepts would revolutionise advances in pharmacotherapeutic research, allowing the selective design of specific molecules to target medical ailments rather than rely upon traditional research into the efficacy of pre-existing herbal medicines.
Categories
There are two main groups of adrenoreceptors, α and β, with 9 subtypes in total:
* α are divided to
α1 (a
Gq coupled receptor) and
α2 (a G
i coupled receptor)
**α
1 has 3 subtypes: α
1A, α
1B and α
1D
**α
2 has 3 subtypes: α
2A, α
2B and α
2C
* β are divided to
β1,
β2 and
β3. All 3 are coupled to
Gs proteins, but β
2 and β
3 also couple to G
i
G
i and G
s are linked to
adenylyl cyclase
Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction:
:A ...
.
Agonist
An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...
binding thus causes a rise in the intracellular concentration of the second messenger (G
i inhibits the production of cAMP)
cAMP
Camp may refer to:
Outdoor accommodation and recreation
* Campsite or campground, a recreational outdoor sleeping and eating site
* a temporary settlement for nomads
* Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...
. Downstream effectors of cAMP include
cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding.
Roles in circulation
Epinephrine (adrenaline) reacts with both α- and β-adrenoreceptors, causing vasoconstriction and vasodilation, respectively. Although α receptors are less sensitive to epinephrine, when activated at pharmacologic doses, they override the vasodilation mediated by β-adrenoreceptors because there are more peripheral α
1 receptors than β-adrenoreceptors. The result is that high levels of circulating epinephrine cause vasoconstriction. However, the opposite is true in the coronary arteries, where β
2 response is greater than that of α
1, resulting in overall dilation with increased sympathetic stimulation. At lower levels of circulating epinephrine (physiologic epinephrine secretion), β-adrenoreceptor stimulation dominates since epinephrine has a higher affinity for the β
2 adrenoreceptor than the α
1 adrenoreceptor, producing vasodilation followed by decrease of peripheral vascular resistance.
Subtypes
Smooth muscle behavior is variable depending on anatomical location. Smooth muscle contraction/relaxation is generalized below. One important note is the differential effects of increased cAMP in smooth muscle compared to cardiac muscle. Increased cAMP will promote relaxation in smooth muscle, while promoting increased contractility and pulse rate in cardiac muscle.
α receptors
α receptors have actions in common, but also individual effects. Common (or still receptor unspecified) actions include:
*
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
* decreased flow of
smooth muscle in
gastrointestinal tract
Subtype unspecific α agonists (see actions above) can be used to treat
rhinitis
Rhinitis, also known as coryza, is irritation and inflammation of the mucous membrane inside the nose. Common symptoms are a stuffy nose, runny nose, sneezing, and post-nasal drip.
The inflammation is caused by viruses, bacteria, irritant ...
(they decrease
mucus secretion). Subtype unspecific α antagonists can be used to treat
pheochromocytoma
Pheochromocytoma (PHEO or PCC) is a rare tumor of the adrenal medulla composed of chromaffin cells, also known as pheochromocytes. When a tumor composed of the same cells as a pheochromocytoma develops outside the adrenal gland, it is referred t ...
(they decrease
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
caused by norepinephrine).
α1 receptor
α
1-adrenoreceptors are members of the G
q protein-coupled receptor superfamily. Upon activation, a
heterotrimeric G protein,
Gq, activates
phospholipase C (PLC). The PLC cleaves
phosphatidylinositol 4,5-bisphosphate
Phosphatidylinositol 4,5-bisphosphate or PtdIns(4,5)''P''2, also known simply as PIP2 or PI(4,5)P2, is a minor phospholipid component of cell membranes. PtdIns(4,5)''P''2 is enriched at the plasma membrane where it is a substrate for a number of ...
(PIP
2), which in turn causes an increase in
inositol triphosphate (IP
3) and
diacylglycerol (DAG). The former interacts with
calcium channel
A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there are also ligand-gated calcium channels.
Comparison tables
The following tables ex ...
s of
endoplasmic and
sarcoplasmic reticulum
The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are kept ...
, thus changing the calcium content in a cell. This triggers all other effects, including a prominent slow after depolarizing current (sADP) in neurons.
Actions of the α
1 receptor mainly involve
smooth muscle contraction. It causes
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
in many
blood vessels
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
, including those of the
skin,
gastrointestinal system
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
,
kidney (
renal artery
The renal arteries are paired arteries that supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle.
The renal arteries carry a large portion of total blood flow to the kidneys. Up to ...
)
and
brain. Other areas of smooth muscle contraction are:
*
ureter
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional ep ...
*
vas deferens
*
hair (
arrector pili muscle
The arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, known colloquially as goose bumps (piloerection).
Structure
E ...
s)
*
uterus (when pregnant)
*
urethral sphincter
The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of th ...
*
urothelium
Transitional epithelium also known as urothelium is a type of stratified epithelium. Transitional epithelium is a type of tissue that changes shape in response to stretching (stretchable epithelium). The transitional epithelium usually appears ...
and
lamina propria
*
bronchioles
The bronchioles or bronchioli (pronounced ''bron-kee-oh-lee'') are the smaller branches of the bronchial airways in the lower respiratory tract. They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start o ...
(although minor relative to the relaxing effect of β
2 receptor on bronchioles)
*blood vessels of ciliary body and (stimulation of dilator pupillae muscles of iris causes
mydriasis
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drugs.
Normally, ...
)
Actions also include
glycogenolysis and
gluconeogenesis from
adipose tissue
Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...
and
liver; secretion from
sweat gland
Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial su ...
s and
Na+ reabsorption from
kidney.
[
α1 antagonists can be used to treat:]
* hypertension – decrease blood pressure by decreasing peripheral vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
* benign prostate hyperplasia
Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, inability to urinate, or loss o ...
– relax smooth muscles
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mu ...
within the prostate thus easing urination
α2 receptor
The α2 receptor couples to the Gi/o protein. It is a presynaptic receptor, causing negative feedback
Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by othe ...
on, for example, norepinephrine (NE). When NE is released into the synapse, it feeds back on the α2 receptor, causing less NE release from the presynaptic neuron. This decreases the effect of NE. There are also α2 receptors on the nerve terminal membrane of the post-synaptic adrenergic neuron.
Actions of the α2 receptor include:
* decreased insulin release from the pancreas
The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an ...
[
* increased glucagon release from the pancreas
* contraction of sphincters of the GI-tract
*]negative feedback
Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by othe ...
in the neuronal synapses - presynaptic inhibition of norepinephrine release in CNS
* increased platelet aggregation (increased blood clotting
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechan ...
tendency)
* decreases peripheral vascular resistance
α2 agonists (see actions above) can be used to treat:
* hypertension – decrease blood pressure-raising actions of the sympathetic nervous system
α2 antagonists can be used to treat:
* impotence – relax penile smooth muscles and ease blood flow
* depression – enhance mood by increasing norepinephrine secretion
β receptors
Subtype unspecific β agonists can be used to treat:
* heart failure – increase cardiac output acutely in an emergency
* circulatory shock
Shock is the state of insufficient blood flow to the tissues of the body as a result of problems with the circulatory system. Initial symptoms of shock may include weakness, fast heart rate, fast breathing, sweating, anxiety, and increased t ...
– increase cardiac output thus redistributing blood volume
*anaphylaxis
Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
– bronchodilation
A bronchodilator or broncholytic (although the latter occasionally includes secretory inhibition as well) is a substance that dilates the bronchi and bronchioles, decreasing resistance in the respiratory airway and increasing airflow to the lung ...
Subtype unspecific β antagonists (beta blocker
Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack (secondary prevention). They are al ...
s) can be used to treat:
* heart arrhythmia – decrease the output of sinus node
The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximate ...
thus stabilizing heart function
* coronary artery disease – reduce heart rate and hence increasing oxygen supply
* heart failure – prevent sudden death related to this condition, which is often caused by ischemias or arrhythmia
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...
s
* hyperthyroidism – reduce peripheral sympathetic hyper-responsiveness
* migraine – reduce number of attacks
*stage fright
Stage fright or performance anxiety is the anxiety, fear, or persistent phobia which may be aroused in an individual by the requirement to perform in front of an audience, real or imagined, whether actually or potentially (for example, when per ...
– reduce tachycardia and tremor
*glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
– reduce intraocular pressure
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk of glaucoma. Most tonometers are calibrated t ...
β1 receptor
Actions of the β1 receptor include:
*increase cardiac output
In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: t ...
by increasing heart rate (positive chronotropic
Chronotropic effects (from ''chrono-'', meaning time, and ''tropos'', "a turn") are those that change the heart rate.
Chronotropic drugs may change the heart rate and rhythm by affecting the electrical conduction system of the heart and the ner ...
effect), conduction velocity (positive dromotropic effect), stroke volume (by enhancing contractility – positive inotropic
An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction.
The term ''inotro ...
effect), and rate of relaxation of the myocardium, by increasing calcium ion sequestration rate (positive lusitropic
Lusitropy is the rate of myocardial relaxation. The increase in cytosolic calcium of cardiomyocytes via increased uptake leads to increased myocardial contractility (positive inotropic effect), but the myocardial relaxation, or lusitropy, decreases ...
effect), which aids in increasing heart rate
*increase renin
Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the ...
secretion from juxtaglomerular cells
Juxtaglomerular cells (JG cells), also known as juxtaglomerular granular cells are cells in the kidney that synthesize, store, and secrete the enzyme renin. They are specialized smooth muscle cells mainly in the walls of the afferent arteriol ...
of the kidney
* increase renin
Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the ...
secretion from kidney
*increase ghrelin secretion from the stomach
β2 receptor
Actions of the β2 receptor include:
* smooth muscle relaxation throughout many areas of the body, e.g. in bronchi
A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchus ...
(bronchodilation, see salbutamol
Salbutamol, also known as albuterol and sold under the brand name Ventolin among others, is a medication that opens up the medium and large airways in the lungs. It is a short-acting β2 adrenergic receptor agonist which works by causing rel ...
), GI tract (decreased motility), veins (vasodilation of blood vessels), especially those to skeletal muscle (although this vasodilator effect of norepinephrine is relatively minor and overwhelmed by α adrenoceptor-mediated vasoconstriction)
* lipolysis in adipose tissue
Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...
*anabolism
Anabolism () is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy, known also as an endergonic process. Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking-do ...
in skeletal muscle
*uptake of potassium into cells
* relax non-pregnant uterus
* relax detrusor urinae muscle
The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to sto ...
of bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine en ...
wall
* dilate arteries
An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the p ...
to skeletal muscle
* glycogenolysis and gluconeogenesis
* stimulates insulin secretion
* contract sphincters
A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the hum ...
of GI tract
* thickened secretions from salivary glands[
* inhibit histamine-release from ]mast cells
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...
* involved in brain - immune communication
β2 agonists (see actions above) can be used to treat:
*asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
and COPD – reduce bronchial smooth muscle contraction thus dilating the bronchus
A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchus. ...
*hyperkalemia
Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occa ...
– increase cellular potassium intake
*preterm birth
Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between ...
– reduce uterine
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ut ...
smooth muscle contractions
β3 receptor
Actions of the β3 receptor include:
*increase of lipolysis in adipose tissue
Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...
*relax the bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine en ...
β3 agonists could theoretically be used as weight-loss drug
Anti-obesity medication or weight loss medications are pharmacological agents that reduce or control weight. These medications alter one of the fundamental processes of the human body, weight regulation, by altering either appetite, or absorpt ...
s, but are limited by the side effect of tremors.
See also
*Beta adrenergic receptor kinase
G-protein-coupled receptor kinase 2 (GRK2) is an enzyme that in humans is encoded by the ''ADRBK1'' gene. GRK2 was initially called Beta-adrenergic receptor kinase (βARK or βARK1), and is a member of the G protein-coupled receptor kinase subfam ...
* Beta adrenergic receptor kinase-2
Notes
References
Further reading
*
External links
Alpha receptors illustrated
The Adrenergic Receptors
Adrenoceptors - IUPHAR/BPS guide to pharmacology
Basic Neurochemistry: α- and β-Adrenergic Receptors
Theory of receptor activation
Desensitization of β1 receptors
{{DEFAULTSORT:Adrenergic Receptor
G protein-coupled receptors