Page 190 - Basic _ Clinical Pharmacology ( PDFDrive )

176 SECTION III Cardiovascular-Renal Drugs

Vasomotor center
Methyldopa
Clonidine
Guanabenz
Guanfacine

Sympathetic nerve terminals
Guanethidine
Guanadrel
Reserpine

Sympathetic ganglia
β-Receptors of heart Trimethaphan
Propranolol and
other β-blockers

Angiotensin α-Receptors of vessels Vascular smooth muscle
receptors of vessels Prazosin and Hydralazine Verapamil and other
Losartan and other α blockers Minoxidil calcium channel
1
other angiotensin Nitroprusside blockers
receptor blockers Diazoxide Fenoldopam

β-Receptors of juxtaglomerular
Kidney tubules cells that release renin
Thiazides, etc Propranolol and
other β blockers

Angiotensin-
converting
enzyme Renin
Angiotensin II Angiotensin I Angiotensinogen

Aliskiren
Captopril and
other ACE inhibitors
FIGURE 11–3 Sites of action of the major classes of antihypertensive drugs.

2. Sympathoplegic agents, which lower blood pressure by reduc- increased efficacy and, in some cases, decreased toxicity. (See Box:
ing peripheral vascular resistance, inhibiting cardiac function, Resistant Hypertension & Polypharmacy.)
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 DRUGS THAT ALTER SODIUM &
sympathetic reflex arc (see below). WATER BALANCE
3. Direct vasodilators, which reduce pressure by relaxing vascular
smooth muscle, thus dilating resistance vessels and—to varying Dietary sodium restriction has been known for many years to
degrees—increasing capacitance as well. decrease blood pressure in hypertensive patients. With the advent
4. Agents that block production or action of angiotensin and of diuretics, sodium restriction was thought to be less important.
However, there is now general agreement that dietary control of
thereby reduce peripheral vascular resistance and (potentially) blood pressure is a relatively nontoxic therapeutic measure and
blood volume. may even be preventive. Even modest dietary sodium restriction
The fact that these drug groups act by different mechanisms lowers blood pressure (though to varying extents) in many hyper-
permits the combination of drugs from two or more groups with tensive persons.