Presynaptic Adrenergic Release Inhibitor


Presynaptic Adrenergic Release Inhibitor, Alpha Adrenergic Central Agonist, Central Adrenergic Agonist, Central Alpha 2 Adrenergic Agonist, Peripheral Acting Presynaptic Adrenergic Antagonist, Peripheral Presynaptic Adrenergic Antagonist, Peripheral Presynaptic Alpha Adrenergic Antagonist

  • Background
  1. Adrenergic Receptor Agonists increase Blood Pressure
    1. Alpha 1 Adrenergic Receptor binding increases Vasoconstriction
    2. Beta 1 Adrenergic Receptor binding increases myocardial contractility
  2. Presynaptic Adrenergic Release Inhibitors lower Blood Pressure
    1. Central Acting Adrenergic Agonists
      1. Activate central alpha-2 receptors that inhibit CNS sympathetic signals
      2. Results in increased parasympathetic effects and side effects
    2. Peripheral Acting Adrenergic Antagonists
      1. Block peripheral Norepinephrine release
  1. Mechanism
    1. See Alpha Adrenergic Receptor
    2. Bind central alpha-2 receptors (vasomotor receptors) to inhibit sympathetic outflow
      1. Decreases Peripheral Vascular Resistance (and Blood Pressure)
      2. Decreases Heart Rate
  2. Non-selective Preparations
    1. Clonidine (Catapres)
    2. Alpha Methyldopa (Aldomet)
    3. Guanfacine (Tenex)
    4. Guanabenz (Wytensin, no longer available in U.S.)
  3. Selective Preparations: Alpha-2a (for Opioid Withdrawal symptoms)
    1. Lofexidine
  • Preparations
  • Peripheral Acting Adrenergic Antagonists
  1. Mechanism
    1. Peripheral Presynaptic Adrenergic Antagonists block Norepinephrine release from postganglionic nerve terminals
    2. Contrast with Postsynaptic Adrenergic Antagonists that block peripheral alpha receptors
      1. Nonselective post-synaptic Alpha Antagonists (Terazosin, Doxazosin, Prazosin) result in general peripheral vasodilation
      2. Selective Alpha-1a Antagonist (Tamsulosin, Alfuzosin, Silodosin) primarily result in Urethral region relaxation
  2. Agents
    1. Reserpine (Serpasil)
    2. Guanethidine (Ismelin)
    3. Guanadrel (Hylorel)
  • References
  1. Olson (2020) Clinical Pharmacology, MedMaster, Miami, p. 64-5