Beta adrenergic agonists or beta agonists are medications that relax muscles of the airways, causing widening of the airways and resulting in easier breathing. They are a class of sympathomimetic agents, each acting upon the beta adrenoceptors. In general, pure beta-adrenergic agonists have the opposite function of

beta blockers 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 ...

: beta-adrenoreceptor agonist ligands mimic the actions of both epinephrine- and

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad' ...

- signaling, in the heart and lungs, and in smooth muscle tissue; epinephrine expresses the higher affinity. The activation of β₁, β₂ and β₃ activates the enzyme,

adenylate 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 ...

. This, in turn, leads to the activation of the secondary messenger

cyclic adenosine monophosphate Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transd ...

(cAMP); cAMP then activates

protein kinase A In cell biology, protein kinase A (PKA) is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP). PKA is also known as cAMP-dependent protein kinase (). PKA has several functions in the cell, including regulatio ...

(PKA) which phosphorylates target proteins, ultimately inducing smooth muscle relaxation and contraction of the cardiac tissue.

Function

Activation of β₁ receptors induces 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 ...

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 ...

output of the cardiac muscle, leading to increased heart rate and blood pressure, secretion of

ghrelin Ghrelin (; or lenomorelin, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases the drive to eat. Blood levels of ghrelin are hi ...

from the stomach, and renin release from the kidneys. Activation of β₂ receptors induces smooth muscle relaxation in the lungs, gastrointestinal tract, uterus, and various blood vessels. Increased heart rate and heart muscle contraction are associated with the β1 receptors; however, β₂ cause vasodilation in the myocardium. β3 receptors are mainly located in adipose tissue. Activation of the β₃ receptors induces the metabolism of lipids.

Medical uses

Indications of administration for β agonists include: * Bradycardia (slow heart rate) *

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 ...

Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

(COPD) * Heart failure *

Allergic reaction Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...

s *

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. Occasi ...

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 ...

poisoning *

Premature labor 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 ...

(this is an off-label use and could be detrimental)

Side effects

Although minor compared to those of epinephrine, beta agonists usually have mild to moderate adverse effects, which include

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

, hypertension, increased heart rate, and

insomnia Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping. They may have difficulty falling asleep, or staying asleep as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, ...

. Other side effects include headaches and

essential tremor Essential tremor (ET), also called benign tremor, familial tremor, and idiopathic tremor, is a medical condition characterized by involuntary rhythmic contractions and relaxations ( oscillations or twitching movements) of certain muscle groups in ...

Hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose bel ...

was also reported due to increased secretion of insulin in the body from activation of β₂ receptors. In 2013, zilpaterol, a β agonist sold by Merck, was temporarily withdrawn due to signs of sickness in some cattle that were fed the drug.

Receptor selectivity

Most agonists of the beta receptors are selective for one or more beta-adrenoreceptors. For example, patients with low heart rate are given beta agonist treatments that are more "cardio-selective" such as dobutamine, which increases the force of contraction of the heart muscle. Patients who are suffering from chronic inflammatory lung diseases such as asthma or COPD may be treated with medication targeted to induce more smooth muscle relaxation in the lungs and less contraction of the heart, including first-generation drugs like salbutamol (albuterol) and later-generation medications in the same class. β₃ agonists are currently under clinical research and are thought to increase the breakdown of lipids in obese patients.

β₁ agonists

β₁ agonists stimulate adenylyl cyclase activity and opening of calcium channel (cardiac stimulants; used to treat cardiogenic shock, acute heart failure, bradyarrhythmias). Selected examples are: *

Denopamine Denopamine ( INN) is a cardiotonic drug which acts as a β1 adrenergic receptor agonist. It is used in the treatment of angina and may also have potential uses in the treatment of congestive heart failure Heart failure (HF), also known as c ...

Dobutamine Dobutamine is a medication used in the treatment of cardiogenic shock (as a result of inadequate tissue perfusion) and severe heart failure. It may also be used in certain types of cardiac stress tests. It is given by IV only, as an injection in ...

Dopexamine Dopexamine is a synthetic analogue of dopamine that is administered intravenously in hospitals to reduce exacerbations of heart failure and to treat heart failure following cardiac surgery. It is not used often, as more established drugs like ...

(β₁ and β₂) * Epinephrine (non-selective) *

Isoprenaline Isoprenaline, or isoproterenol (brand name: Isoprenaline Macure), is a medication used for the treatment of bradycardia (slow heart rate), heart block, and rarely for asthma. It is a non-selective β adrenoceptor agonist that is the isopropyla ...

(

INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they also provided accommo ...

), isoproterenol (

USAN 280px, "Samguk Sagi" Book 04. Silla's Records. In 512, Usan-guk（于山國）was Ulleungdo（鬱陵島） Usan-guk, or the State of Usan, occupied Ulleung-do and the adjacent islands during the Korean Three Kingdoms period. According to th ...

) (β₁ and β₂) * Prenalterol *

Xamoterol Xamoterol is a cardiac stimulant. It works by binding to the β1 adrenergic receptor. It is a 3rd generation adrenergic β receptor partial agonist In pharmacology, partial agonists are drugs that bind to and activate a given receptor, but ha ...

β₂ agonists

β₂ agonists stimulate adenylyl cyclase activity and closing of calcium channel (smooth muscle relaxants; used to treat asthma and COPD). Selected examples are: *

Arformoterol Arformoterol, sold under the brand name Brovana among others, is a medication used for the treatment of chronic obstructive pulmonary disease (COPD). It is a long-acting β2 adrenoreceptor agonist (LABA) and it is the active (''R'',''R'')-(−) ...

* Buphenine *

Clenbuterol Clenbuterol is a sympathomimetic amine used by sufferers of breathing disorders as a decongestant and bronchodilator. People with chronic breathing disorders such as asthma use this as a bronchodilator to make breathing easier. It is most commonl ...

(β₁ and β₂) * Epinephrine (non-selective) *

Fenoterol Fenoterol is a β adrenoreceptor agonist. It is classed as sympathomimetic β2 agonist and an inhaled bronchodilator asthma medication. Fenoterol is produced and sold by Boehringer Ingelheim as Berotec N and in combination with ipratropium as ...

Formoterol Formoterol, also known as eformoterol, is a long-acting β2 agonist (LABA) used as a bronchodilator in the management of asthma and chronic obstructive pulmonary disease (COPD). Formoterol has an extended duration of action (up to 12 h) co ...

* Isoetarine *

(

), isoproterenol (

) (β₁ and β₂) * Levosalbutamol (

), levalbuterol (

) *

Orciprenaline Orciprenaline, also known as metaproterenol, is a bronchodilator used in the treatment of asthma. Orciprenaline is a moderately selective β2 adrenergic receptor agonist that stimulates receptors of the smooth muscle in the lungs, uterus, and va ...

(

), metaproterenol (

) *

Pirbuterol Pirbuterol (trade name Maxair) is a short-acting β2 adrenoreceptor agonist with bronchodilating action used in the treatment of asthma, available (as pirbuterol acetate) as a breath-activated metered-dose inhaler. It was patented in 1971 a ...

* Procaterol *

Ritodrine Ritodrine (trade name Yutopar) is a tocolytic drug used to stop premature labor. This drug has been removed from the US market, according to FDA Orange Book. It was available in oral tablets or as an injection and was typically used as the hyd ...

* Salbutamol (

), albuterol (

) *

Salmeterol Salmeterol (sold in China as Qitai) is a long-acting β2 adrenergic receptor agonist (LABA) used in the maintenance and prevention of asthma symptoms and maintenance of chronic obstructive pulmonary disease (COPD) symptoms. Symptoms of bronchos ...

Terbutaline Terbutaline, sold under the brand names Bricanyl and Marex among others, is a β2 adrenergic receptor agonist, used as a "reliever" inhaler in the management of asthma symptoms and as a tocolytic (anti-contraction medication) to delay preterm ...

Undetermined/unsorted

These agents are also listed as agonists by

MeSH A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands. Types * A plastic mesh may be extruded, oriented, exp ...

. * Arbutamine * Befunolol * Bromoacetylalprenololmenthane * Broxaterol * Cimaterol *

Cirazoline Cirazoline is a full agonist at the α1A adrenergic receptor, a partial agonist at both the α1B and α1D adrenergic receptors, and a nonselective antagonist to the α2 adrenergic receptor. It is believed that this combination of properties ...

* Etilefrine *

Hexoprenaline Hexoprenaline is a selective β2 adrenergic receptor agonist used in the treatment of asthma. Hexoprenaline is also used in some countries (such as Russia and Switzerland) as a tocolytic agent (i.e., labor suppressant), with the most common tra ...

Higenamine Higenamine (norcoclaurine) is a chemical compound found in a variety of plants including '' Nandina domestica'' (fruit), ''Aconitum carmichaelii'' (root), '' Asarum heterotropioides'', '' Galium divaricatum'' (stem and vine), ''Annona squamosa'' ...

Isoxsuprine Isoxsuprine (used as isoxsuprine hydrochloride) is a drug used as a vasodilator in humans (under the trade name Duvadilan) and equines. Isoxsuprine is a β2 adrenoreceptor agonist that causes direct relaxation of uterine and vascular smooth musc ...

* Mabuterol * Methoxyphenamine * Oxyfedrine *

Ractopamine Ractopamine () is an animal feed additive used to promote leanness and increase food conversion efficiency in farmed animals in several countries, but banned in others. Pharmacologically, it is a phenol-based TAAR1 agonist and Beta-adrenergic ag ...

* Reproterol * Rimiterol * Tretoquinol * Tulobuterol * Zilpaterol * Zinterol

References

{{Receptor agonists and antagonists