ADRENERGIC SYSTEM

ADRENERGIC RECEPTORS Alpha receptors (α) – α1 & α2

Beta receptors (β) – β1 , β2 & β3

Dopamine receptors (D) – D1 to D5

Receptor type Location & FunctionPostsynaptic α1

Smooth muscles – Contraction Blood vessels – Vasoconstriction Radial muscle of iris – Mydriasis Salivary glands – Secretion Gut – Relaxation Liver - Glycogenolysis

Receptor type Location & Function

Presynaptic α2 Adrenergic & Cholinergic nerve endings – decreases the release of neurotransmitters

Postsynaptic α2 Blood vessels – Constriction

Ciliary epithelium – decreases aqueous secretion by the ciliary body

Receptor type Location & Function

Postsynaptic β1 Heart – increases heart rate and force of contraction

Postsynaptic β2 Smooth muscles ( bronchi, bladder wall, blood vessels, pregnant uterus ) – Relaxation Liver – glycogenolysis VasodilatationIncreases the secretions of ciliary epithelium

Postsynaptic β3 Adipocytes – stimulates lipolysis Thermogenesis

Adrenergic drugs:Pressor agents – Noradrenaline, dopamine,

phenylephrine, ephedrineCardiac stimulants – Adrenaline, isoprenalineBronchodilators – salbutamol, terbutalineNasal decongestants – Phenylephrine,

xylometazoline, oxymetazoline, naphazolineCNS stimulants – AmphetamineAnorectics – Fenfluramine, sibutramineUterine relaxants – Ritodrine, isoxsuprine

PHARMACOLOGICAL ACTIONS Heart : Increase in heart rate, force of contraction,

conduction velocity , cardiac output Rise in BP Vascular effects : α action – vasoconstriction (cutaneous, renal,

viscera, mucous membrane)β2 action – vasodilatation (skeletal muscle,

liver, coronaries)

Effects on smooth muscles :

a. Bronchi – bronchodilatation and decreases secretion and relieves mucosal congestion

b. Gut – relaxationc. Urinary tract – detrusor muscle relaxation contraction of trigone and sphincter Hinders micturition. d. Uterus – Non-pregnant –contraction Pregnant – Relaxation

Metabolic effects :a. Glycogenolysis in liver& skeletal muscle – hyperglycemiab. Increase in FFA due to lipolysis in adipose

tissuec. Inhibition of insulin release Eye:Active mydriasisDecreases intraocular pressure

Therapeutic uses- Acute anaphylactic shock- adrenaline

- life saving drug Bronchial asthma To prolong the duration of local

anaesthetic action – adrenaline +LA As a local haemostatic- epistaxis &

capillary oozing Cardiac resuscitation- cardiac arrest

due to drowning, electrocution- i.v. adrenaline

Glaucoma- dipivefrine(prodrug)

ADRENERGIC RECEPTOR ANTAGONISTS

Adrenergic receptor antagonists

Alpha-blockers Beta-blockers

ALPHA BLOCKERS

ALPHA-BLOCKERS1) Non-selective(α1 and α2) blockers Reversible: Phentolamine Irreversible: Phenoxybenzamine

2) Selective α1-blockers;Prazosin, terazosin, doxazosin, tamsulosin

3) Selective α2-blockers; Yohimbine

USES OF ΑLPHA-BLOCKERS1) Pheochromocytoma Phenoxybenzamine ( preoperatively) 2) Hypertensive emergencies3) Tissue necrosis Phentolamine4) Male sexual dysfunction 5) Essential hypertension - α1-blockers- less tachycardia & favorable effects on lipid profile

6) Benign prostatic hyperplasia

ΒETA BLOCKERS

Classification:o Non-selective (β1 & β2) blockers :• Propranolol• Timolol• Sotalol• Nadolol• Pindolol

Selective β1 Blockers : • Atenolol• Acebutolol• Bisoprolol • Esmolol• Metoprolol

Selective β2 blocker :

. Butoxamine

β blockers with additional α blocking/

vasodilator property

• Labetalol• Carvedilol• Celiprolol• Nebivolol

Pharmacological actions:

CVS : cardiac β1 receptor blockade –

HR, FOC, conduction velocity – decreases CO cardiac work load & myocardial O2 demand

S-A node & A-V nodal activity – depressed

Automaticity of heart – suppressed

Chronic use – BP in hypertensive patients.

Respiratory tract :

• In asthmatics - Blockade of β2 receptors in bronchial smooth muscle. Severe bronchoconstrictionEye: o Decreases aqueous humor secretion - IOP in glaucoma.

Therapeutic uses of β-blockers :

Hypertension- preferred in patients with angina, MI Advantages: Less sodium water retention Longer duration of action Cheaper, well tolerated

Angina pectoris Cardiac arrhythmias- mainly in atrial arrhythmias

Congestive heart failure- carvedilol, metoprolol, bisoprolol decreases mortalilty rate

Pheochromocytoma- to control cardiac manifestations but should be given alone

Glaucoma – reduce production of aqueous humor Timolol, carteolol, levobunolol, betaxolol Timolol- does not affect pupil size, longer duration of action, well tolerated

Prophylaxis of migraine

Hyperthyroidism

Essential tremors

Acute anxiety states

Alcohol withdrawal

Adverse effects

Bradycardia

Bronchoconstriction – Bronchial asthma & COPD

Sleep disturbances, hallucinations, fatigue & mental depression

Hypoglycemia – patients receiving insulin &

oral hypoglycemic drugs.

Muscular weakness

Abrupt withdrawal symptoms

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