Adrenergic drugs

1. INTRODUCTION TO AUTONOMIC PHARMACOLOGY:
 The nervous system is divided into central and peripheral
nervous systems. The peripheral nervous system consists
of autonomic and somatic nervous systems.
CENTRAL NERVOUS
SYSTEM
PERIPHERAL NERVOUS
SYSTEM
AUTONOMIC SOMATIC
PARASYMPATHETIC
SYMPATHETIC
NERVOUS SYSTEM

2.  The prime functions of adrenergic or
sympathetic nervous system is to
help the human beings to adjust to
stress and prepare the body for fight
of flight reactions.
 Neurotransmitters for the
sympathetic system are
noradrenaline and dopamine.
Adrenaline is the major hormone
secreted by the adrenal medulla.
 Synthesis of catecholamines:
 The catechlamines noradrenaline,
adrenaline and dopamine are
synthesized from the amino acid
tyrosine
TYROSINE
DOPA
DOPAMINE
NORADRENALINE
ADRENALINE
TYROSINE
HYDROXILASE
DOPA
DECARBOXYLASE
DA BETA
HYDROXYLASE
N-METHYL
TRANSFERASE

3.  The sympathetic post ganglionic nerve fibres that
synthesize, store and release NA are called adrenergic.
 Noradrenaline is stored in small vesicles in the adrenergic
nerve terminals.
 In response to nerve impulse, NA is released into the
synaptic cleft by a process of exocytosis. This NA binds to
adrenergic receptors located on the post synaptic
membrane to produce response.

4. ADRENERGIC DRUGS: (SYMPATHOMIMETICS)
 Sympathomimetics are drugs whose actions mimic that of
sympathetic stimulation.
 Chemical classification:
 Catecholamines: noradrenaline, adrenaline, dopamine.
 Non-catecholamines: ephedrine, amphetamine.
 Depending on mode of actions:
 Directly acting: noradrenaline, isoprenaline, dopamine.
 Indirectly acting: amphetamine, tyramine.
 Mixed action amines:
 Ephidrine, methoxamine.

5. Adrenaline:
 Cardio vascular system: It is a powerful cardiac stimulant.
 It increases the heart rate, force of conduction and cardiac
output by acting through β1 receptors.
 They constrict the blood vessels of mucous membrane α2.
And dilate the blood vessels of skeletal muscles β2.
 It also causes renal, pulmonary and mesentric
vasoconstriction.
 Smooth muscles: Adrenaline is a powerful brocho
constrictor and weak respiratory stimulant.
 Relaxes gut smooth muscles.

6.  Eye: Adrenaline causes mydriasis due to contraction of the
radial muscles of the iris. It also reduces intra ocular
pressure.
 Metabolic effects: Adrenaline increases blood sugar level
by enhancing hepatic glycogenolysis. It also inhibits
insulin release.
 Adverse reactions: anxiety, palpitation, tremors, dizziness,
restlessness and headache. Rapid IV injection may cause
sudden sharp rise in BP which may precipitate
arrhythmias, subarachnoid hemorrhage or hemiplegia
 Uses: anaphylactic shock, cardiac arrest, control of
hemorrhage. Also used along with local anesthetics. Used
along with bronchial asthma and glaucoma

7. Ephedrine:
 Is an alkaloid obtained from plants of the genus ephedra.
 It acts by direct stimulation of α and β receptors and
indirectly through release of noradrenaline.
 Adverse effects: stomach upset, sleeplessness, tremors,
difficulty in micturition.
 Uses: bronchial asthma, nasal decongestion, mydriasis,
hypotension, narcolepsy, nocturnal enuresis.

8. ADRENERGIC BLOCKING AGENTS:
 These drugs binds to the adrenergic receptors and prevent
the action of adrenergic drugs. They nay block alpha and
beta receptors and both.
 Alpha adrenergic blocking agents:
 α1-blockade: inhibits vasocontriction-leading to vasodilation
and thereby decreasing BP. This fall in BP is opposed by the
barroreceptor reflexes which tend to increase in increase
heart rate and cardiac out put.
 α2-blockade: enhances release of NA which stimulates β
receptors. β1 stimulation results in tachycardia and increases
cardiac output.
 Adverse effects: postural hypotension, palpitation, nasal
stiffness, miosis and impaired ejaculation (impotence)

9. CLASSIFICATION:
 Non-selective:
 Non-competitive blockers: phenobenzamine.
 competitive blockers: ergotamine, phentolamine,
 Selective:
 α1 blockers: prazosin, terazocin.
 α2 blockers: yohimbine.
 Phenoxy benzamine: binds covalently to alpha receptors
causing irreversible blockade.
 Give IV BP falls gradually and is associated with tachycardia.
 Ergot alkaloids: ergotamine and their derivatives are
competitive α receptor antagonists and the blockade is of
short duration.

10.  Beta adrenergic blocking agents:
 Beta blockers are the drugs that block the action of
catecholamines mediated through beta receptors.
 Classification:
 Non-selective: propranolol, nadolol, temolol.
 Cardio selective: metoprolol, atenolol, esmolol.
 Partial agonists: pindolol, oxprenolol.
 With additional alpha blocking property: labetalol.
 Actions:
 CVS blockers: decrease heart rate, force of contraction and
cardiac output. BP falls. AV conduction is delayed.
Myocardial oxygen demand is reduced due to reduced
cardiac work.

11.  Exercise: beta blockers prevent increase in heart rate and
force of contraction which are brought about by exercise.
 Respiratory tract: blockade of beta 2 receptors in
bronchial smooth muscle causes increase in airway
resistance- may precipitate acute attacks in asthmatics.
 Eye: many beta blockers reduce intraocular pressure by
decreased secretion of aqueous humor.
 Adverse reactions: bradycarida, CCF, cold extremities,
CNS sedation, metabolic effects. Rebound hypertension,
and acute asthmatic attacks.
 Uses: hypertension , angina pectoris, cardiac arrhythmias,
myocardial infarction, obstructive cardiomyopathy,
glaucoma, prophylaxis of migraine, anxiety.