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 (arrhythmia), and to protect the heart from a second heart attack after a first heart attack (secondary prevention). ...

: beta-adrenoreceptor agonist ligands mimic the actions of both

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 a ...

- and

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...

- 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, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine tri ...

(cAMP); cAMP then activates

protein kinase A In cell biology, protein kinase A (PKA) is a family of serine-threonine kinases 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, in ...

(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 or inotropic is a drug or any substance 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 co ...

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 cardiac cycle, rhythm by affecting the electrical conduction system of the hea ...

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

ghrelin Ghrelin (; or lenomorelin, INN) is a hormone primarily 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 ghrel ...

from the stomach, and

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 reni ...

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 Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due ...

(slow heart rate) *

Asthma Asthma is a common 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 wh ...

Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory s ...

(COPD) *

Heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

Allergic reaction Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food al ...

s *

Hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0 mmol/L (3.5 and 5.0 mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Oc ...

Beta blocker Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms ( arrhythmia), and to protect the heart from a second heart attack after a first heart attack ( secondary prevention ...

poisoning *

Premature labor Preterm birth, also known as premature birth, is the Childbirth, birth of a baby at fewer than 37 weeks Gestational age (obstetrics), gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 ...

(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 characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

, increased heart rate, and

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

. Other side effects include

headache A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of Depression (mood), depression in those with severe ...

s 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 i ...

Hypoglycemia Hypoglycemia (American English), also spelled hypoglycaemia or hypoglycæmia (British English), sometimes 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 tria ...

was also reported due to increased secretion of insulin in the body from activation of β₂ receptors. In 2013,

zilpaterol Zilpaterol is a synthetic β2 adrenergic agonist. Under its brand name, Zilmax, it is used to increase the size of cattle and the efficiency of feeding them. Zilmax is produced by Intervet, a subsidiary of Merck & Co., and marketed as a "beef-i ...

, 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 "cardioselective" 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 *

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 ...

* Dopexamine (β₁ and β₂) *

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 a ...

(non-selective) *

Isoprenaline Isoprenaline, also known as isoproterenol and sold under the brand name Isuprel among others, is a sympathomimetic medication which is used in the treatment of acute bradycardia (slow heart rate), heart block, and rarely for asthma, among other ...

(

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 accomm ...

), isoproterenol ( USAN) (β₁ and β₂) * Prenalterol * Xamoterol

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 * Buphenine * Clenbuterol * Dopexamine (β₁ and β₂) *

(non-selective) * Fenoterol * Formoterol * Isoetarine *

(

), isoproterenol ( USAN) (β₁ and β₂) * Levosalbutamol (

), levalbuterol ( USAN) * Orciprenaline (

), metaproterenol ( USAN) * Pirbuterol * Procaterol * Ritodrine *

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 that causes relaxation of ...

(

), albuterol ( USAN) * Salmeterol *

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 ...

β₃ agonists

Undetermined/unsorted

These agents are also listed as agonists by

MeSH Medical Subject Headings (MeSH) is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences. It serves as a thesaurus of index terms that facilitates searching. Created and updated by th ...

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

Etilefrine Etilefrine, sold under the brand name Effortil among others, is a sympathomimetic medication used as an antihypotensive agent to treat orthostatic hypotension. It is usually used oral administration, by mouth, but is also available as an injecti ...

* Hexoprenaline * Higenamine * Isoxsuprine * Mabuterol * Methoxyphenamine * Oxyfedrine * Ractopamine * Reproterol * Rimiterol * Tretoquinol * Tulobuterol *

Zilpaterol Zilpaterol is a synthetic β2 adrenergic agonist. Under its brand name, Zilmax, it is used to increase the size of cattle and the efficiency of feeding them. Zilmax is produced by Intervet, a subsidiary of Merck & Co., and marketed as a "beef-i ...

* Zinterol

References

External links

* {{Receptor agonists and antagonists