Chapter: Modern Pharmacology with Clinical Applications: Antihypertensive Drugs
Drugs That Impair Sympathetic Nervous System Functioning
DRUGS THAT
IMPAIR SYMPATHETIC NERVOUS SYSTEM FUNCTIONING
The drugs discussed in this
section reduce blood pres-sure by depressing the activity of the sympathetic
nerv-ous system. This is accomplished in four ways: (1) by re-ducing the number
of impulses traveling in the sympathetic nerves, (2) by inhibiting
neurotransmitter release, (3) by depleting the stores of norepinephrine, and
(4) by antagonizing the actions of norepinephrine on effector cells. The sites
of action of these drugs are diverse and may best be appreciated by considering
the sympathetic arc concerned with blood pressure regula-tion (Fig. 20.2).
While there may be some
involvement of the adren-ergic nervous system in primary hypertension, there is
no clear evidence that a malfunction of this system is causally involved in
primary hypertension. Therefore, even
though drugs may depress the sympathetic system and thus lower blood pressure,
it should not be assumed that this
therapeutic approach corrects the cause of the el-evated pressure. Only in
a few specific cases, such as pheochromocytoma,
can hypertension be directly re-lated to abnormalities in the functioning of
the sympa-thetic system.
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