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An adrenergic is a drug, or other substance, which has effects similar to, or the same as, epinephrine (adrenaline). Thus, they are a kind of sympathomimetic agents. Alternatively, it may refer to something which is susceptible to epinephrine, or similar substances, such as a biological receptor (specifically, the adrenergic receptors).

Beta blockers block the action of epinephrine and norepinephrine in the body. Adrenergic drugs either stimulate a response (agonists) or inhibit a response (antagonists). The five categories of adrenergic receptors are: α₁, α₂, β₁, β₂, and β₃, and agonists vary in specificity between these receptors, and may be classified respectively. However, there are also other mechanisms of adrenergic agonism. Epinephrine and norepinephrine are endogenous and broad-spectrum. More selective agonists are more useful in pharmacology.

α₁ agonists

Main article: Alpha-1 adrenergic receptor#agonists

α₁ agonists: stimulates phospholipase C activity. (vasoconstriction and mydriasis; used as vasopressors, nasal decongestants & eye exams). Selected examples are:

• Methoxamine
• Methylnorepinephrine
• Oxymetazoline
• Phenylephrine

α₂ agonists

Main article: Alpha-2 adrenergic receptor#agonists

α₂ agonists: inhibits adenylyl cyclase activity. (reduce brainstem vasomotor center-mediated SNS activation; used as antihypertensives, sedatives & treatment of opiate & alcohol withdrawal symptoms). Selected examples are:

• Clonidine (mixed alpha2-adrenergic and imidazoline-I1 receptor agonist)
• Guanfacine (preference for alpha2A-subtype of adrenoceptor)
• Guanabenz (most selective agonist for alpha2-adrenergic as opposed to imidazoline-I1)
• Guanoxabenz (metabolite of guanabenz)
• Guanethidine (periferal alpha2-receptor agonist)

β₁ agonists

Main article: Beta-1 adrenergic receptor#agonists

β₁ agonists: stimulates adenylyl cyclase activity; opening of calcium channel. (cardiac stimulants; used to treat cardiogenic shock, acute heart failure, bradyarrhythmias). Selected examples are:

• Dobutamine
• Isoproterenol (β₁ and β₂)

β₂ agonists

Main article: Beta-2 adrenergic receptor#agonists

β₂ agonists: stimulates adenylyl cyclase activity; closing of calcium channel (smooth muscle relaxants; used to treat asthma and COPD). Selected examples are:

• salbutamol (albuterol in USA)
• Fenoterol
• Formoterol
• Isoproterenol (β₁ and β₂)
• Metaproterenol
• Salmeterol
• Terbutaline
• Clenbuterol

Other mechanisms

• Indirect action
  • Amphetamine
  • Tyramine
• Mixed action
  • Ephedrine

See also

• Adrenergic receptor

External links

• Virtual Chembook article on adrenergic drugs
• MeSH adrenergic+agonists

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• This page was last modified on 22 April 2008, at 21:48.

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