Guide To Adrenergic Signaling

OVERVIEW

This page is dedicated to covering the broad topic of adrenergic signaling.

WHAT IS IT?

Adrenergic signaling fundamentally means signaling within the body that involves adrenaline (epinephrine) or noradrenaline (norepinephrine). It is not necessary to make the topic any more confusing then that!

Adrenergic receptors are found on various tissues in the body, and are bound by epinephrine and norepinephrine. They are G-coupled protein receptors, and they are the medium by which the signaling pathway operates. There are various different classes of adrenergic receptors that we will be discussed in more detail below.

  • Alpha-1 (α1) receptors
  • Alpha-2 (α2) receptors
  • Beta-1 (β1) receptors
  • Beta-2 (β2) receptos
ALPHA-1 RECEPTORS

The function of these receptors will vary upon the target organ. Below are examples of what occurs at different sites of the body when this adrenergic receptor is activated/agonized.

  • Peripheral vasculature: constriction occurs and systemic blood pressure increases.
  • Bladder: contraction of internal urethral sphincter
  • Eye: contraction of the pupillary dilator useless (mydriasis)

Medications that agonize these receptors:

  • Epinephrine 
  • Norepinephrine 
  • Phenylephrine 
  • Methoxamine
ALPHA-2 RECEPTORS

The function of these receptors will vary upon the target organ. Below are examples of what occurs at different sites of the body when this adrenergic receptor is activated/agonized.

 

BETA-1 RECEPTORS

The function of these receptors will vary upon the target organ. Below are examples of what occurs at different sites of the body when this adrenergic receptor is activated/agonized.

  1. Heart: the heart rate, contractility, and conductance of the heart will all increase.
  2. The kidneys (renal juxtaglomerular cells)

Not found in:

  • Vascular smooth muscle 

Medications that agonize these receptors:

  • Epinephrine
  • Dopamine
  • Dobutamine
  • Isoproterenol
BETA-2 RECEPTORS

Type of receptor:

Gs protein couple receptor that activates adenyl cycles and increases intracellular cAMP concentrations (in the presence of its ligand). 

The function of these receptors will vary upon the target organ. Below are examples of what occurs at different sites of the body when this adrenergic receptor is activated/agonized.

  • Peripheral vasculature (skeletal muscle): relaxation of the skeletal muscle will cause vasodilation and decreased diastolic blood pressure
  • Bronchi: bronchodilatation
  • Uterus: relaxation (tocolysis)

Medications that agonize these receptors:

  • Isoproterenol
  • Terbutaline 
  • Ritodrine
MEDICATIONS

Nonselective alpha and beta blockers:

Non-selective alpha blockers:

  • Phenoxybenzamine: irreversible. 
  • Phentolamine: reversible 

 

Page Updated: 07.31.2016