Beta-adrenergic agonist

Beta adrenergic receptor agonists
Drug class
Skeletal structor formula of salbutamol (albuterol) — a widely used medication to treat asthma attacks
Class identifiers
Use	Bradycardia, Asthma, heart failure, etc.
ATC code	R03
Biological target	Adrenergic receptors (β subtype)
External links
MeSH	D000318

Beta adrenergic agonists or Beta agonists are medications that relax muscles of the airways, which widens the airways and results in easier breathing. They are a class of sympathomimetic agents which act upon the beta adrenoceptors. In general, pure beta-adrenergic agonists have the opposite function of beta blockers. Beta adrenoreceptor agonist ligands mimic the action of epinephrine and norepinephrine signaling in the heart, lungs and smooth muscle tissue, with epinephrine expressing the highest affinity. The activation of β₁, β₂ and β₃ activates the enzyme, adenylate cyclase. This in turn leads to the activation of the secondary messenger cyclic adenosine monophosphate (cAMP), cAMP then activates Protein Kinase A (PKA) which phosphorylates target proteins ultimately inducing smooth muscle relaxation and contraction of the cardiac tissue.

Activation of β₁ receptors induces positive inotropic, chronotropic output of the cardiac muscle, leading to increased heart rate and blood pressure, secretion of ghrelin 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 is also associated with the β2 receptors.

β3 receptors are mainly located in adipose tissue. Activation of the β₃ receptors induces the metabolism of lipids.

Indications of administration for β agonists include the following:

Although minor compared to those of epinephrine, beta agonists usually have mild to moderate adverse effects, which include anxiety, hypertension, increased heart rate and insomnia. Other side effects include headaches and essential tremor. Indications of hypoglycemia were also reported due to secretion of insulin in the body from activation of β₂ receptors.