PHARMACOLOGY OF ANTIHYPERTENSIVE AGENTS
antihypertensive agents act at one or more of the four ana-tomic control sites
depicted in Figure 11–1 and produce their effects by interfering with normal
mechanisms of blood pressure regulation. A useful classification of these
agents categorizes them according to the principal regulatory site or mechanism
on which they act (Figure 11–3). Because of their common mechanisms of action,
drugs within each category tend to produce a similar spec-trum of toxicities.
The categories include the following:
Diuretics, which lower blood
pressure by depleting the bodyof sodium and reducing blood volume and perhaps
by other mechanisms.
2. Sympathoplegic agents, which lower blood pressure by reduc-ing peripheral vascular resistance, inhibiting cardiac function, and increasing venous pooling in capacitance vessels. (The lat-ter two effects reduce cardiac output.) These agents are further subdivided according to their putative sites of action in the sympathetic reflex arc .
3. Direct vasodilators, which reduce pressure by relaxing vascu-lar smooth muscle, thus dilating resistance vessels and—to varying degrees—increasing capacitance as well.
Agents that block
production or action of angiotensin andthereby reduce peripheral vascular
resistance and (potentially) blood volume.
fact that these drug groups act by different mechanisms permits the combination
of drugs from two or more groups with increased efficacy and, in some cases,
decreased toxicity. (See Box: Resistant Hypertension & Polypharmacy.)