5. Mechanism of action of the adrenergic agonists
Direct-acting Indirect- acting
Selective Non-selective Ephedrine Amphetamine
α1:phenylephrine
α2: Alpha methyl Dopa
β1:dobutamine
β2:salbutamol
α1,α2,β1,β2:adrenaline
α1,α2,β1: noradrenaline
β1,β2: isoprinaline
Sympathomimetic drugs
Drugs have effects similar to those produced by activity of
sympathetic nerve stimulation
6. Mechanism of action of the
adrenergic agonists
Mechanism of action of the
adrenergic agonists
Lippincott’s pharmacology 4th
edition
7. Effects of sympathetic stimulationEffector organs Effects of sympathetic stimulation
Eye Mydriasis
Heart ↑ heart rate
↑ force of contraction
↑ blood pressure
Blood vessels Dilatation of coronary arteries
Dilatation of blood vessels supply skeletal
muscle
Stomach and Intestine Inhibits Peristalsis and the tone of↑
sphincters and inhibits defecation
Urinary bladder Relaxes bladder wall
↑ the tone of sphincters inhibits
micturation
Respiratory system Dilatation of bronchi
liver Glycogenlysis
8. Adrenaline
α1, α2, β1 and β2 agonist
Can be administered by :
-- subcutaneous -- inhalation -- eye drops -- intracardiac
Actions similar to sympathetic stimulation
Cardiovascular system
Heart : ↑all cardiac properties (↑contractility, heart rate , AV
conduction, excitability, automaticity
Blood vessels:
• Vasoconstriction (skin, mucous membrane, renal)
• Vasodilatation (skeletal muscle, coronary blood vessels)
Blood pressure:
• ↑systolic blood pressure, ↓ diastolic blood pressure
9. Adrenaline actions (cont.)
Respiratory system
Bronchodilatation (β2)
Decongestion of bronchial mucosa (α1)
urinary bladder and Gastrointestinal
tract
Spasm of spincters (α1)
Relaxation of the wall (β2)
urinary retention and inhibits defecation
Skeletal muscle
Facilitate NM transmission
Vasodilatation (β2)
10. Adrenaline actions (cont.)
Eye
Vasoconstriction of conjunctival blood vessels
(decongestion)
↓intraocular pressure
Mydriasis
Antiallergic
Adrenaline is Physiological antagonist of histamine
Metabolism
Increase blood glucose
Lipolysis
General stimulation of metabolic activity
11. Adrenaline
Uses
With local anesthetic (delay absorption and prolong
duration of drugs)
Open angle glaucoma (eye drops)
Epistaxis (haemostatic nasal pack)
Anaphylactic shock
Cardiac resuscitation in cardiac arrest
Acute bronchial asthma
12. Adrenaline
Adverse effects
Gangrene if injected around finger toes
Hypertension , leads to cerebral hemorrhage
Tachycardia, palpitation, angina and arrhythmia
Contraindications
Injection Around finger or toe
Hypertension
coronary heart disease
Arrhythmia
Hemorrhagic shock
Thyrotoxicosis
15. Dobutamine (dobutrex)
Selective β1agonist
positive inotropic ↑ Cardiac output
Used by I.V. infusion in treatment of
-Cardiogenic shock,
-Resistant heart failure
-Resistant heart block.
Side effects:
Angina and arrhythmias
16. Phenylephrine
Selective α1 – agonists
Example :
Action
stimulates α-receptors leading to VC and ↑ blood pressure
VC of mucous membrane blood vessels so promote drainage in
nasal passages
Uses:
Nasal congestion,
Hypotensive states (shock)
To prolong action of local anesthetics
Fundoscopic examination of eye
Adverse effects :
Mydriasis Urine retention
17. Alpha methyl Dopa (Aldomet)
Selective α2 – agonists
Agonists of α2 receptors in VMC in brain leading to:
↓ sympathetic Outflow from vaso Motor Centre (VMC)
↓ heart rate, ↓ CO (cardiac out put), ↓ PR ↓
BP
It inhibits synthesis of catecholamine, dopamine and
serotonin .
Uses
Hypertension especially in: Renal impairment.
Pregnancy.