Adrenergic Receptors and Their Clinical Applications

Adrenergic Receptors

• Adrenergic receptors are a type of G protein-coupled receptor that respond to the neurotransmitter norepinephrine (NE) and the hormone epinephrine (EPI)
• There are two main categories: α (alpha) and β (beta) receptors

Alpha Adrenergic Receptors

• Subtypes: α1, α2
• α1 receptors:
  • Stimulate smooth muscle contraction
  • Increase blood pressure
  • Vasoconstriction
• α2 receptors:
  • Inhibit neurotransmitter release (including NE)
  • Decrease blood pressure
  • Sedation and relaxation

Beta Adrenergic Receptors

• Subtypes: β1, β2, β3
• β1 receptors:
  • Increase heart rate and contractility
  • Stimulate renin release
• β2 receptors:
  • Relax smooth muscle (bronchodilation, vasodilation)
  • Increase glucose release from liver and muscle
• β3 receptors:
  • Lipolysis (breakdown of fat)

Adrenergic Agonists

• Stimulate adrenergic receptors
• Examples:
  • Epinephrine (EPI): non-selective α and β agonist
  • Norepinephrine (NE): non-selective α and β agonist
  • Phenylephrine: selective α1 agonist
  • Isoproterenol: non-selective β agonist
  • Albuterol: selective β2 agonist

Adrenergic Antagonists

• Block adrenergic receptors
• Examples:
  • Phentolamine: non-selective α antagonist
  • Prazosin: selective α1 antagonist
  • Propranolol: non-selective β antagonist
  • Metoprolol: selective β1 antagonist

Clinical Applications

• Treatment of hypertension, angina, and heart failure
• Management of asthma and chronic obstructive pulmonary disease (COPD)
• Anesthesia and surgery
• Treatment of attention deficit hyperactivity disorder (ADHD)