Skip to Main Content

++

INTRODUCTION

++

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).

Image not available.

++

CLASSIFICATION

++
A. 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 Graphic Jump Location
TABLE 9–1Types of adrenoceptors, some of the peripheral tissues in which they are found, and their major effects.
++
B. Mode of Action
++

Sympathomimetic agonists may directly activate their adrenoceptors, or they may act indirectly to increase the concentration of endogenous catecholamine transmitter in the synapse. Amphetamine derivatives and tyramine cause the release of stored catecholamines; they are therefore mainly indirect in their mode of action. Cocaine and the tricyclic antidepressants exhibit another form of indirect action; these drugs inhibit reuptake of catecholamines by the norepinephrine transporter (NET) and the dopamine transporter (DAT) in nerve terminals (see Figure 6–2) and thus increase the synaptic activity of released transmitter.

++

Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print
High-Yield Terms to Learn
Anorexiant A drug that decreases appetite (causes anorexia)
Catecholamine A dihydroxyphenylethylamine derivative (eg, norepinephrine, epinephrine), a relatively polar molecule that is readily metabolized by catechol-O-methyltransferase
Decongestant An α-agonist ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.