The drugs discussed in this section reduce blood pressure by depressing the activity of the sympathetic nervous system. This is accomplished in four ways: (1) by reducing 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 regulation (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
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