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Drugs Modifying Adrenergic Transmission



α Methyl-p-tyrosine

Inhibits tyrosine hydroxylase (The rate-limiting enzyme)

Depletes catecholamines


α Methyldopa

Inhibits dopa decarboxylase

Instead of noradrenaline, α methyl adrenaline is produced

A false transmitter

Does not stimulate receptor


Guanethidine & Bretylium

Inhibit nerve impulse coupled release of neurotransmitters

Decreased adrenergic activity


Receptor agonists e.g. phenylephrine, salbutamol etc.

Stimulate receptors

Increased adrenergic activity


Receptor antagonists e.g. phentolamine, propranolol etc.

Block receptors

Decreased adrenergic activity


Cocaine & Desipramine

Inhibit axonal uptake by NET

Noradrenaline stays in synaptic cleft

More stimulation of the receptors

Increased adrenergic activity


Reserpine

Inhibits vesicular uptake by VMAT

More noradrenaline stays in cytoplasm

Degraded by MAO

Decreased adrenergic activity


Amphetamine, Tyramine etc

Displaces noradrenaline from its storage sites

Noradrenaline moves into cytoplasm

Reverse transport & exchange diffusion

More noradrenaline in the synaptic space

Stimulation of receptors

Increased adrenergic activity


MAO inhibitors e.g. tranylcypromine

Inhibits MAO

Catecholamines are not degraded


COMT inhibitors

Inhibits COMT

Catecholamines are not degraded

 

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