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The sympathomimetics constitute a very important group of drugs used for cardiovascular, respiratory, and other conditions. They are readily divided into subgroups on the basis of their spectrum of action (α-, β-, or dopamine-receptor affinity) or mode of action (direct or indirect).

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AnorexiantA drug that decreases appetite (causes anorexia)
CatecholamineA dihydroxyphenylethylamine derivative (eg, norepinephrine, epinephrine), a relatively polar molecule that is readily metabolized by catechol-O-methyltransferase
DecongestantAn α-agonist drug that reduces conjunctival, nasal, or oropharyngeal mucosal vasodilation by constricting blood vessels in the submucosal tissue
MydriaticA drug that causes dilation of the pupil; opposite of miotic
PhenylisopropylamineA derivative of phenylisopropylamine (eg, amphetamine, ephedrine). Unlike catecholamines, phenylisopropylamines usually have oral activity, a long half-life, CNS activity, and cause release of stored catecholamines
Selective α agonist, β agonistDrugs that have relatively greater effects on α or β adrenoceptors; none are absolutely selective or specific
SympathomimeticA drug that mimics stimulation of the sympathetic autonomic nervous system
Reuptake inhibitorAn indirect-acting drug that increases the activity of transmitters in the synapse by inhibiting their reuptake into the presynaptic nerve ending. May act selectively on noradrenergic, serotonergic, or both types of nerve endings

Spectrum of Action

Adrenoceptors are classified as α, β, or dopamine receptors; these groups are further subdivided into subgroups. The distribution of these receptors is set forth in Table 9–1. Epinephrine may be considered a single prototype agonist with effects at all α- and β-receptor types. Alternatively, separate prototypes, phenylephrine (an α agonist) and isoproterenol (β) may be defined. The just-mentioned drugs have relatively little effect on dopamine receptors, but dopamine itself is a potent dopamine receptor agonist and, when given as a drug, can also activate β receptors (intermediate doses) and α receptors (larger doses).

Table 9–1 Types of Adrenoceptors, Some of the Peripheral Tissues in Which They Are Found, and Their Major Effects.

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