Sympathomimetic drugs

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Epinephrine

Norepinephrine

Sympathomimetic drugs are substances that mimic the effects of the hormone epinephrine (adrenaline) and the hormone/neurotransmitter norepinephrine (noradrenaline). They all raise blood pressure and are all weak bases. The drugs include:

• Clonidine
• Cyclopentamine
• Fenfluramine
• Isoproterenol
• Parahydroxyamphetamine
• Phenylephrine
• Tetrahydrozoline

Mechanisms of action

The mechanisms of sympathomimetic drugs are to act as catecholamine synthesis precursors, norepinephrine transporter blockade, adrenergic receptor agonism, inhibition of epinephrine and norepinephrine metabolism and/or cholinergic inhibition.

Synthesis precursor

Synthesis precursors of catecholamines stimulate the catecholamine synthesis. One example is levodopa.

Norepinephrine transporter blockade

Classical sympathomimetic drugs are amphetamines (including MDMA), ephedrine and cocaine, which act by blocking and reversing norepinephrine transporter (NET) activity. NET is a transport protein expressed on the surface of some cells that clears noradrenaline and adrenaline from the extracellular space and into cells, terminating the signaling effects.

Adrenergic receptor agonism

Main article: Adrenergic agonist

Direct stimulation of the α- and β-adrenergic receptors can produce sympathomimetic effects. Albuterol is a very commonly used direct-acting β_2-agonist.

Inhibition of epinephrine and norepinephrine metabolism

Inhibition of norepinephrine or epinephrine metabolism can produce sympathomimetic effects. Both are mainly metabolized by the enzyme monoamine oxidase, the monoamine oxidase inhibitor (MAOI) drugs can induce such effects. COMT inhibitors can also decrease metabolism of norepinephrine and epinephrine.

Cholinergic inhibition

Sympathomimetic drugs may also work by inhibiting the opposite system, i.e. the parasympathetic system. It does so by inhibiting the effects of acetylcholine, e.g. by inhibiting synaptic vesicle release, antagonize acetylcholine receptors,

• synaptic vesicle release inhibitors:
  • botulinum toxin
• ACh receptor inhibitors
  • atropine (all muscarinic)
  • scopolamine (M1 receptors)
  • tubocurarine (Muscle type nicotinic

Cross-reactivity

Substances like cocaine also affect dopamine, and some substances like MDMA affect serotonin.

Norepinephrine is synthesized by the body into epinephrine, causing central nervous system stimulation. Thus, all sympathomimetic amines fall into the larger group of stimulants (see psychoactive drug chart). Many of these stimulants have therepeutic use and abuse potential, can induce tolerance, and possibly physical dependence.

See also

• Adrenergic drugs
• Prostaglandins
• Sympathetic nervous system
• Sympatholytic drugs

External links

• MeSH Amines,+Sympathomimetic
• Dictionary at eMedicine Sympathomimetic+amine
• Dictionary at eMedicine Sympathomimetic

Sympathomimetic amines
Benzylpiperazine Cathinone Chlorphentermine Cocaine Diethylpropion Ephedrine Fenfluramine Mazindol Methylone Methylphenidate Pemoline Phendimetrazine Phenmetrazine Phentermine Phenylephrine Propylhexedrine Pseudoephedrine Sibutramine Synephrine
Amphetamines 4-FMP Amphetamine Benzphetamine Dextroamphetamine dl-Amphetamine MDMA MDA MDEA Methamphetamine Paramethoxyamphetamine

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