"Beta agonist" redirects here
|Beta Adrenergic receptor agonists|
Skeletal structor formula of Salbutamol. A widely used medication to treat asthma attacks
|Use||Bradycardia, Asthma, heart failure, etc.|
|Biological target||Adrenergic receptors (β subtype)|
Beta-adrenergic agonists are a class of sympathomimetic agents which act upon the beta adrenoreceptors. 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 being 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 and induces 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.
Medical uses 
Indications of beta agonists include the following:
- Hypoglycemia (low blood sugar)
- Bradycardia (slow heart rate)
- Hypotension (low blood pressure)
- Chronic obstructive pulmonary disease (COPD)
- Heart failure
- allergic reactions
- an antidote to beta blocker poisoning
Side effects 
Although minor compared to epinephrine, beta agonists usually have mild to moderate adverse effects, which includes anxiety, hypertension, increased heart rate and insomnia. Other side effects include headaches and essential tremor.
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 induces the force of constriction of the heart muscle. Patients who are suffering from a chronic inflammatory lung diseases such as asthma or chronic obstructive pulmonary disease, are treated with albuterol, which mainly induces smooth muscle relaxation in the lungs and less contraction of the heart. Beta 3 agonists are currently in clinical research and are thought to increase the breakdown of lipids in obese patients.
β1 agonists 
β1 agonists: stimulates adenylyl cyclase activity; opening of calcium channel. (cardiac stimulants; used to treat cardiogenic shock, acute heart failure, bradyarrhythmias). Selected examples are:
β2 agonists 
β2 agonists: stimulates adenylyl cyclase activity; closing of calcium channel (smooth muscle relaxants; used to treat asthma and COPD). Selected examples are:
- salbutamol (albuterol in USA)
- Levosalbutamol (Levalbuterol in USA)
- Isoproterenol (β1 and β2)