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.