USMLE

Alpha-2 (Adrenergic) Receptors

6,859 views
General Pharm
  1. Gs / Gi Pathway
  2. Gq Signaling Pathway
  3. Alpha-1 (Adrenergic) Receptors
  4. Alpha-2 (Adrenergic) Receptors
  5. Beta-1 (Adrenergic) Receptors
  6. Beta-2 (Adrenergic) Receptors
  7. Beta-3 (Adrenergic) Receptors
  8. M1 (Muscarinic) Receptors
  9. M2 (Muscarinic) Receptors
  10. M3 (Muscarinic) Receptors
  11. D1 (Dopamine) Receptors
  12. D2 (Dopamine) Receptors
  13. H1 (Histamine) Receptors
  14. H2 (Histamine) Receptors
  15. V1 (Vasopressin) Receptors
  16. V2 (Vasopressin) Receptors

Summary

Alpha-2 receptors are adrenergic receptors, meaning that they bind norepinephrine and epinephrine. Binding causes the activation of a Gi protein subunit, which inhibit adenylate cyclase, decreasing cAMP. This will lead to a number of clinical effects, including decreased sympathetic outflow, decreased insulin release, and decreased aqueous humor production. Alpha-2 receptor agonists use these effects to treat hypertension, ADHD, and glaucoma.

Key Points

  • Alpha-2 Receptors
    • Signaling
      • Use the Gi signaling pathway
        • → decreased cAMP
    • Outcomes 
      • Decreased sympathetic outflow
      • Decreased insulin release
        • Via alpha-2 on pancreas
          • Beta-2 increases insulin release, but alpha-2 is normally predominant (so sympathetic stimulation inhibits insulin secretion)
      • Decreased aqueous humor production
      • Increased platelet aggregation (lower yield)
      • Decreased lipolysis (lower yield)