Alpha-2 (Adrenergic) Receptors



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)