The adrenomimetic drugs mimic the effects of adren-ergic sympathetic nerve stimulation on sympathetic effectors; these drugs are also referred to as sympatho-mimetic agents. The adrenergic transmitter norepineph-rine and the adrenal medullary hormone epinephrine also are included under this broad heading. The adrenomimetic drugs are an important group of thera-peutic agents that can be used to maintain blood pres-sure or to relieve a life-threatening attack of acute bronchial asthma. They are also present in many over-the-counter cold preparations because they constrict mucosal blood vessels and thus relieve nasal congestion.
The adrenomimetic drugs can be divided into two ma-jor groups on the basis of their chemical structure: the catecholamines and the noncatecholamines. The cate-cholamines include norepinephrine, epinephrine, and dopamine, all of which are naturally occurring, and sev-eral synthetic substances, the most important of which is isoproterenol (isopropyl norepinephrine). The skele- tal structure of the catecholamines is shown in Figure 10.1.
The L-isomers are the naturally occurring forms of epinephrine and norepinephrine and possess consid-erably greater pharmacological effects than do the D-isomers. Throughout most of the world, epinephrine and norepinephrine are known as adrenaline and nora-drenaline, respectively.
Noncatecholamine adrenomimetic drugs differ from the basic catecholamine structure primarily by having substitutions on their benzene ring.