Sympathetic Receptors

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 G& 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
α
2
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

Module Below Start Quiz

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