- Sympathomimetic drug
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DopamineSympathomimetic drugs are substances that mimic the effects of the catecholamines epinephrine(adrenaline), norepinephrine(noradrenaline), and/or dopamine. Such drugs are used to treat cardiac arrest, low blood pressure, or even delay premature labor, among other things.
These drugs act at the
postganglionicsympathetic terminal,cite web |url=http://www.mercksource.com/pp/us/cns/cns_hl_dorlands_split.jsp?pg=/ppdocs/us/common/dorlands/dorland/eight/000103504.htm |title=Dorlands Medical Dictionary:sympathomimetic |format= |work= |accessdate=] either directly activating postsynapticreceptors, blocking breakdown and reuptake, or stimulating production and release of catecholamines.
Mechanisms of action
The mechanisms of sympathomimetic drugs can be direct-acting, such as α-adrenergic agonists, β-adrenergic agonists,
dopaminergic agonists; or indirect-acting, such as MAOIs, COMTs, release stimulants, and reuptake inhibitors.
Adrenergic receptor agonists
Direct stimulation of the α- and β-
adrenergic receptors can produce sympathomimetic effects. Albuterolis a very commonly used direct-acting β2-agonist. Other examples include phenylephrine, isoproterenol, and dobutamine.
Stimulation of the
D1 receptorby dopaminergic agonists such as fenoldopamis used intravenously to treat hypertensive crisis.
Norepinephrine transporter blockade
Classical sympathomimetic drugs are
amphetamines(including MDMA), ephedrineand 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 spaceand into cells, terminating the signaling effects.
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.
cocainealso affect dopamine, and some substances like MDMAaffect serotonin.
Norepinephrine is synthesized by the body into epinephrine, causing
central nervous systemstimulation. Thus, all sympathomimetic amines fall into the larger group of stimulants (see psychoactive drugchart). Many of these stimulants have therepeutic use and abuse potential, can induce tolerance, and possibly physical dependence.
Parasympatholytic" and "sympathomimetic" are similar, but not identical. For example, both cause mydriasis, but parasympatholytics reduce accommodation ( cycloplegia) while sympathomimetics do not.
Sympathetic nervous system
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