Medicine & USMLE

Alpha-1 (Adrenergic) Receptors

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


Alpha-1 adrenergic receptors are G-protein coupled receptors that make up the sympathetic response in the autonomic nervous system. When a ligand binds to the Alpha-1 receptor, it’s corresponding Gq protein will trigger a cascade of downstream messengers, including phospholipase C, IP3, and DAG. Since alpha-1 receptors are found on smooth muscle, activation of these receptors will lead to muscle contraction, such as vasoconstriction, pupil dilation, and bladder sphincter constriction. 

Key Points

  • Alpha-1 Receptors
    • Signaling
      • Use the Gq signaling pathway
    • Outcomes
      • Vasoconstriction
      • Mydriasis (pupil dilation)
      • Urinary sphincter contraction (less urine)