Beta-2 adrenergic receptor agonists
β2 adrenergic receptor agonists relax smooth muscles of bronchi and uterus and blood vessels of skeletal muscles. At high doses may exhibit β1 action on heart.
Tachycardia is common after systemic administration which is due to the agonistic action of β1 receptors.
Long term use of β2 receptor agonists, may result in their down regulation with subsequent decreased pharmacological response.
Important selective β2– adrenoceptor stimulant include clenbuterol, terbutaline, isoxuprine, salbutamol (albuterol) and orciprenaline ( metaproterenol). Salbutamol has highest ratio of β2: β1action ( about 10 times)
Note
β2 adrenergic receptor agonists are primarily used as bronchodilators and as uterine relaxants to delay premature labor.