A number of adrenomimetic amines are not cate-cholamines. Some of these are directly acting amines that must interact with adrenoceptors to produce a response in effector tissues. Some directly acting compounds, such as phenylephrine and methoxamine, activate a-adrenoceptors almost exclusively, whereas others, like albuterol and terbutaline, are nearly pure p-adrenoceptor agonists. Drugs that exert their pharmacological actions by releasing norepinephrine from its neuronal stores (indirectly acting) produce effects that are similar to those of norepinephrine. They tend to exert strong a-adrenoceptor activity, but pj-adrenoceptor activity typical of norepinephrine, such as myocardial stimulation, also occurs.
Some of the indirectly acting adrenomimetic amines are used primarily for their vasoconstrictive properties. They are applied locally to the nasal mucosa or to the eye. Other amines are used as bronchodilators, while still others are used exclusively for their ability to stimulate the CNS. Many noncatecholamine adrenomimetic amines resist enzymatic destruction, have prolonged actions, and are orally effective. The indirectly acting drugs are effective only when given in large doses, and they often produce tachyphylaxis.
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