Adrenergic Receptors in the Sympathetic Nervous System

Adrenergic Receptors

• Also known as adrenoceptors
• A class of G protein-coupled receptors that respond to the neurotransmitters norepinephrine and epinephrine
• Play a crucial role in the sympathetic nervous system, regulating various physiological processes such as:
  • Heart rate and blood pressure
  • Vasoconstriction and vasodilation
  • Smooth muscle contraction and relaxation
  • Metabolic rate and energy expenditure

Types of Adrenergic Receptors

• Alpha-1 (α1) receptors:
  • Mediate vasoconstriction, smooth muscle contraction, and pupil dilation
  • Found in smooth muscle, vascular endothelium, and iris
• Alpha-2 (α2) receptors:
  • Mediate negative feedback on norepinephrine release, decreasing sympathetic activity
  • Found in presynaptic neurons, pancreatic islets, and adipose tissue
• Beta-1 (β1) receptors:
  • Mediate increased heart rate and contractility
  • Found in heart, kidney, and adipose tissue
• Beta-2 (β2) receptors:
  • Mediate smooth muscle relaxation, bronchodilation, and vasodilation
  • Found in smooth muscle, airway epithelium, and vascular endothelium
• Beta-3 (β3) receptors:
  • Mediate lipolysis and thermogenesis
  • Found in adipose tissue

Adrenergic Drugs

• Sympathomimetics:
  • Stimulate adrenergic receptors, mimicking the effects of norepinephrine and epinephrine
  • Examples: ephedrine, phenylephrine, pseudoephedrine
• Alpha-1 agonists:
  • Increase blood pressure and vasoconstriction
  • Examples: midodrine, phenylephrine
• Alpha-2 agonists:
  • Decrease blood pressure and sympathetic activity
  • Examples: clonidine, guanabenz
• Beta-1 agonists:
  • Increase heart rate and contractility
  • Examples: dobutamine, isoproterenol
• Beta-2 agonists:
  • Relax smooth muscle and dilate airways
  • Examples: salbutamol, terbutaline
• Beta-3 agonists:
  • Increase lipolysis and thermogenesis
  • Examples: mirabegron
• Alpha blockers:
  • Block alpha-1 receptors, decreasing vasoconstriction and blood pressure
  • Examples: prazosin, terazosin
• Beta blockers:
  • Block beta-1 and beta-2 receptors, decreasing heart rate and contractility
  • Examples: propranolol, metoprolol

Adrenergic Receptors

• Respond to neurotransmitters norepinephrine and epinephrine
• Crucial in sympathetic nervous system, regulating:
  • Heart rate and blood pressure
  • Vasoconstriction and vasodilation
  • Smooth muscle contraction and relaxation
  • Metabolic rate and energy expenditure

Types of Adrenergic Receptors

• Alpha-1 (α1) receptors:
  • Mediate vasoconstriction, smooth muscle contraction, and pupil dilation
  • Found in smooth muscle, vascular endothelium, and iris
• Alpha-2 (α2) receptors:
  • Mediate negative feedback on norepinephrine release, decreasing sympathetic activity
  • Found in presynaptic neurons, pancreatic islets, and adipose tissue
• Beta-1 (β1) receptors:
  • Mediate increased heart rate and contractility
  • Found in heart, kidney, and adipose tissue
• Beta-2 (β2) receptors:
  • Mediate smooth muscle relaxation, bronchodilation, and vasodilation
  • Found in smooth muscle, airway epithelium, and vascular endothelium
• Beta-3 (β3) receptors:
  • Mediate lipolysis and thermogenesis
  • Found in adipose tissue

Functions of Adrenergic Receptors

• Alpha-1 receptors:
  • Increase blood pressure
  • Stimulate smooth muscle contraction
  • Dilate pupils
• Alpha-2 receptors:
  • Decrease sympathetic activity
  • Decrease norepinephrine release
• Beta-1 receptors:
  • Increase heart rate
  • Increase cardiac contractility
• Beta-2 receptors:
  • Relax smooth muscle
  • Dilate airways
  • Cause vasodilation
• Beta-3 receptors:
  • Increase lipolysis
  • Increase thermogenesis

Adrenergic Drugs

• Sympathomimetics:
  • Stimulate adrenergic receptors
  • Examples: ephedrine, phenylephrine, pseudoephedrine
• Alpha-1 agonists:
  • Increase blood pressure and vasoconstriction
  • Examples: midodrine, phenylephrine
• Alpha-2 agonists:
  • Decrease blood pressure and sympathetic activity
  • Examples: clonidine, guanabenz
• Beta-1 agonists:
  • Increase heart rate and contractility
  • Examples: dobutamine, isoproterenol
• Beta-2 agonists:
  • Relax smooth muscle and dilate airways
  • Examples: salbutamol, terbutaline
• Beta-3 agonists:
  • Increase lipolysis and thermogenesis
  • Examples: mirabegron
• Alpha blockers:
  • Block alpha-1 receptors, decreasing vasoconstriction and blood pressure
  • Examples: prazosin, terazosin
• Beta blockers:
  • Block beta-1 and beta-2 receptors, decreasing heart rate and contractility
  • Examples: propranolol, metoprolol