Sympathomimetic drugs (also known asadrenergic drugs andadrenergic amines) are stimulant compounds which mimic the effects ofendogenousagonists of thesympathetic nervous system. Examples ofsympathomimetic effects include increases inheart rate,force of cardiac contraction, andblood pressure.[1] The primary endogenous agonists of the sympathetic nervous system are thecatecholamines (i.e.,epinephrine [adrenaline],norepinephrine [noradrenaline], anddopamine), which function as bothneurotransmitters andhormones. Sympathomimetic drugs are used to treatcardiac arrest and lowblood pressure, delaypremature labor, psychiatric conditions such asADHD, neurological conditions such asnarcolepsy, among other things.
These drugs can act through several mechanisms, such as directly activatingpostsynapticreceptors, blocking breakdown andreuptake of certain neurotransmitters, or stimulating production and release of catecholamines.
The mechanisms of sympathomimetic drugs can be direct-acting (direct interaction between drug and receptor), such asα-adrenergic agonists,β-adrenergic agonists, anddopaminergic agonists; or indirect-acting (interaction not between drug and receptor), such asMAOIs,COMT inhibitors, release stimulants, and reuptake inhibitors that increase the levels of endogenous catecholamines.
A primary or secondary aliphatic amine separated by 2 carbons from a substituted benzene ring is minimally required for high agonist activity. The pKa of the amine is approximately 8.5-10.[2] The presence of hydroxy group in the benzene ring at 3rd and 4th position shows maximum alpha- and beta-adrenergic activity.[medical citation needed]
For maximum sympathomimetic activity, a drug must have:
The structure can be modified to alter binding. If the amine is primary or secondary, it will have direct action, but if theamine is tertiary, it will have poor direct action. Also, if the amine has bulky substituents, then it will have greater beta adrenergic receptor activity, but if the substituent is not bulky, then it will favor the alpha adrenergic receptors.
Direct stimulation of the α- and β-adrenergic receptors can produce sympathomimetic effects.Salbutamol is a widely used direct-actingβ2-agonist. Other examples includephenylephrine,isoproterenol, anddobutamine.
Stimulation of theD1 receptor by dopaminergic agonists such asfenoldopam is used intravenously to treathypertensive crisis.
Dopaminergic stimulants such asamphetamine,ephedrine, andpropylhexedrine work by causing the release of dopamine and norepinephrine, along with (in some cases) blocking the reuptake of these neurotransmitters.
Illegal drugs such ascocaine andMDMA also affectdopamine,serotonin, andnorepinephrine.
Norepinephrine is synthesized by the body from the amino acid tyrosine,[3] and is used in the synthesis of epinephrine, which is a stimulating neurotransmitter of thecentral nervous system.[4] All sympathomimetic amines fall into the larger group ofstimulants (seepsychoactive drug chart). In addition to intended therapeutic use, many of these stimulants haveabuse potential, can inducetolerance, and possiblyphysical dependence, although not by the same mechanism(s) as opioids orsedatives. The symptoms of physical withdrawal from stimulants can include fatigue, dysphoric mood, increased appetite, vivid or lucid dreams, hypersomnia or insomnia, increased movement or decreased movement, anxiety, and drug craving, as is apparent in the rebound withdrawal from certainsubstituted amphetamines.
Sympathomimetic drugs are sometimes involved in development of cerebral vasculitis and generalized polyarteritis nodosa like diseases involving immune-complex deposition. Known reports of such hypersensitivity reactions include the use ofpseudoephedrine,[5]phenylpropanolamine,[6]methamphetamine[7] and other drugs at prescribed doses as well as at over-doses.
"Parasympatholytic" and "sympathomimetic" have similar effects, but through completely different pathways. For example, both causemydriasis, but parasympatholytics reduceaccommodation (cycloplegia) while sympathomimetics do not.[medical citation needed]
If a drug causes effects similar to the activation of the sympathetic nervous system, it is called a sympathomimetic [...] A sympathomimetic agent increases heart rate, force of cardiac contraction and blood pressure.
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