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ADRENERGIC DRUGS |
The adrenergic drugs (several of which are produced in the adrenal gland) are powerful, naturally occurring chemicals that act to excite the body, that is, they increase heart rate and blood pressure, excite the brain, increase blood sugar levels, dilate the pupil of the eye, diminish appetite and food digestion , and reduce blood flow to the extremeties of the body. All these pharmacologic actions are part of the human "flight or flight" response to severely stressful situations.
ADRENERGIC NERVES are those in the heart, bronchi or intestines that release adrenergic compounds, the 2 most important of which are EPINEPHRINE ("epi"), and norepinephrine ("norepi" or simply, NE). Epi and norepi are synonymous with adrenaline and noradrenaline, respectively. Epi and norepi, along with dopamine (an important excitatory agent in the brain) are also termed CATECHOLAMINES (because they are amines with a catechol ring structure).
In order to explain differences in pharmacologic action between different adrenergic drugs, the receptor sites for these drugs (located in various body tissues) are classified as either ALPHA or BETA. Alpha-adrenergic receptors are involved in smooth muscle contraction. Beta-adrenergic receptors respond especially to epinephrine; their stimulation results in relaxation of smooth muscle and stimulation of cardiac (heart) muscle. A well known beta-adrengeric receptor-blocking drug is propranolol (Inderal). You can now understand why Inderal is used to treat patients suffering from extra systoles.
Adrenergic drugs are removed from the tissues by either being reabsorbed back into the vesicles from which they were released, or by being chemically destroyed by oxidation in a reaction catalyzed by the enzyme monoamine oxidase (MAO). Now you should be able to figure out why MAO inhibitors are sometimes given to patients with mental depression.
The AMPHETAMINES (and other related synthetic drugs) are often described as SYMPATHOMIMETICS, i.e., drugs that mimic stimulation of the sympathetic division of the autonomic nervous system. It is this system that mediates our "fight or flight" response. Hence the amphetamines are adrenergic drugs quite similar to the catecholamines.
PSEUDOEPHEDRINE and PHENYLPROPANOLAMINE (PPA) are potent synthetic sympathomimetic drugs that have been used in diet aids and cold treatments. Beware of how much you ingest, as they are potentially dangerous drugs. Actually, PPA has been removed from the market by the Food and Drug Administration because of its associated risk of hemorrhagic stroke.
This discussion of adrenergic drugs is brief and introductory. For a more complete story, see my book, "Drugs and the Human Body", 7th Edition, Prentice Hall.. | | |
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