sympathomimetic drug

sympathomimetic drug

sympathomimetic drug, any of a group of substances whose actions resemble the response of stimulated sympathetic nerves (see nervous system). These drugs include epinephrine and other catecholamines that are naturally produced in the body, and chemically similar substances such as ephedrine. Sympathomimetic drugs excite the central nervous system and heart and affect the diameter of blood vessels. They are used as decongestants and to alleviate bronchial asthma. Because they inhibit the production of the body substance histamine, they are prescribed for allergic conditions along with antihistamines.
Sympathomimetic 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 postganglionic sympathetic terminal, either directly activating postsynaptic receptors, 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.

Direct-acting

Adrenergic receptor agonists

Direct stimulation of the α- and β-adrenergic receptors can produce sympathomimetic effects. Albuterol is a very commonly used direct-acting β2-agonist. Other examples include phenylephrine, isoproterenol, and dobutamine.

Dopaminergic agonists

Stimulation of the D1 receptor by dopaminergic agonists such as fenoldopam is used intravenously to treat hypertensive crisis.

Indirect-acting

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.

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.

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.

Comparison

"Parasympatholytic" and "sympathomimetic" are similar, but not identical. For example, both cause mydriasis, but parasympatholytics reduce accommodation (cycloplegia) while sympathomimetics do not.

See also

References

External links

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