Site icon New

SYMPATHETIC RECEPTORS

amit18289

SYMPATHETIC RECEPTORS

INTRODUCTION:
  • Adrenergic receptors/adrenoceptors/Sympathetic receptors – Class of G protein-coupled receptors.
    • Targets catecholamines, mainly norepinephrine (noradrenaline) & epinephrine (adrenaline).
    • Cells binds to catecholamine receptors & stimulates sympathetic nervous system. 
  • Sympathetic nervous system – 
    • Responsible for fight-or-flight response, including pupil diltation, increasing heart rate, mobilizing energy, & blood-flow divertion from non-essential organs to skeletal muscle.

RECEPTOR TYPES:

  • α receptors:
  • Subtypes 
    • α1 (a Gq coupled receptor) 
    • α2 (a Gi coupled receptor)
    • Phenylephrine – Selective α-receptor agonist.
  • β receptors:
  • Subtypes:
    • β1, β2 and β3. 
    • All three linked to Gs proteins (although β2 also couples to Gi & to adenylate cyclase. 
    • Agonist binding causes raised intracellular second messenger cAMP concentration. 
    • Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates intracellular events following hormone binding.
    • Isoprenaline – non-selective agonist.
Receptor Location Selected action Mechanism Agonist Antagonist
 α1 Vascular , GU smooth muscle

Liver

Intestinal Smooth muscle

Heart

  • Smooth muscle contraction, 
  • Mydriasis,
  • Vasoconstriction in the skin, mucosa & abdominal viscera
  • Sphincter contraction of the GI tract and urinary bladder
  Gq: 

phospholipase C(PLC) activated, 

IP3,and DAG,

↑ calcium

  •  Noradrenaline
  • Phenylephrine
  • Methoxamine
  • Cirazoline
  • Xylometazoline
  • Midodrine
  • Metaraminol
  • Chloroethylclonidine 
  
  • Acepromazine
  • Alfuzosin
  • Doxazosin
  • Phenoxybenzamine
  • Phentolamine
  • Prazosin
  • Tamsulosin
  • Terazosin
  • Trazodone

(TCAs)

  • Amitriptyline
  • Clomipramine
  • Doxepin
  • Trimipramine
  • Typical and atypical antipsychotics

Antihistamines (H1 antagonists)

  • Hydroxyzine
 α2 β-cell of pancreas

Platelet

Nerve Terminal

Vascular smooth muscle

  • Smooth muscle mixed effects,
  • Norepinephrine (noradrenaline) inhibition, 
  • Platelet activation
  Gi: 

adenylate cyclase inactivated, 

cAMP↓

  • Agmatine
  • Dexmedetomidine
  • Medetomidine
  • Romifidine
  • Clonidine
  • Chloroethylclonidine
  • Brimonidine
  • Detomidine
  • Lofexidine
  • Xylazine
  • Tizanidine
  • Guanfacine
  • Amitraz
  
  • Phentolamine
  • Yohimbine
  • Idazoxan
  • Atipamezole
  • Trazodone
  • Typical and atypical antipsychotics
 β1  Juxtraglomular cell

Heart 

  • Positive Chronotropic, Dromotropic and inotropic effects 
  • Increased amylase secretion
  Gs: 

adenylate cyclase activated, 

cAMP↑

  • Dobutamine
  • Isoprenaline
  • Noradrenaline
  
  • Metoprolol
  • Atenolol
  • Bisoprolol
  • Propranolol
  • Timolol
  • Nebivolol
  • Vortioxetine
 β2  Smooth muscle (GI,GU,Vascular,Braonchial)

Skeletal Muscle

  •  Smooth muscle relaxation (Ex. Bronchodilation)
  Gs: 

adenylate cyclase activated, 

cAMP↑

  • Salbutamol
  • Bitolterol mesylate
  • Formoterol
  • Isoprenaline
  • Levalbuterol
  • Metaproterenol
  • Salmeterol
  • Terbutaline
  • Ritodrine
  
  • Butoxamine
  • Timolol
  • Propranolol
  • ICI-118,551
 β3  Adipose Tissue
  • Enhance lipolysis,
  • Promotes relaxation of detrusor muscle in the bladder
  Gs: 

adenylate cyclase activated, 

cAMP↑

  •  L-796568
  • Amibegron
  • Solabegron
  • Mirabegron
  
  • SR 59230A

Exam Important

  • Adreneric β receptors having lipolysis property in fat cells is Beta -3.
  • Alpha 2 agonist cause analgesia & not hyperalgesia.
  • Salmeterol is long acting beta-2-agonist.
  • Beta-2-agonist causes a brief spell of hyperkalemia followed by hypokalemia.
  • Beta-2-agonist doesn’t cause hypoglycemia.
  • Alpha-2-agonist causes Sedation, Glaucoma & Hypertension.
  • Beta-1 receptors in heart stimulates its contractions.
  • Beta-2 receptors are present in smooth muscles.
  • Beta-1 receptors stimulation releases renin.
  • Beta blockers are used to treat hyperthyroidism (Not hypothyroidism).
Don’t Forget to Solve all the previous Year Question asked on SYMPATHETIC RECEPTORS
Click Here to Start Quiz

Share this:

Exit mobile version