20.9j Adrenergic Inhibiting Agents

adrenergic stimulation

Inhibiting the effects of (?) can also control hypertension.

beta-adrenergic antagonism

Several broad mechanisms accomplish this: (?), centrally acting alpha-adrenergic antagonism, adrenergic neuron blockade, α1 blockade, and alpha/beta blockade.

juxtaglomerular cells

From Table 20-17 in our earlier discussion of β1 blockers, you will recall that most β1 receptors are in the heart but some also exist in the (?) of the kidney.

Selective β1 blockade

(?) is useful in treating hypertension for several reasons.

contractility

It decreases (?), thereby directly decreasing cardiac output.

reflex tachycardia

It also reduces (?) by inhibiting sympathetically induced compensatory increases in heart rate.

renin release

Finally, it represses (?) from the kidneys, which, in turn, inhibits the vasoconstriction activated by the renin–angiotensin–aldosterone system.

metoprolol (Lopressor)

The prototype selective β1 blocker is (?); the prototype nonselective beta blocker is propranolol (Inderal).

side effects

The section on β1 blockers discussed these agents’ (?).

Centrally acting adrenergic inhibitors

(?) reduce hypertension by inhibiting CNS stimulation of adrenergic receptors.

CNS α2 agonists

In effect, they are (?).

presynaptic end terminals

Recall that α2 receptors are located on the (?) in the sympathetic nervous system.

norepinephrine

When stimulated, they inhibit the release of (?) to counterbalance sympathetic stimulation.

sympathetic stimulation

By increasing the stimulation of α2 receptors in the section of the CNS responsible for cardiovascular regulation, centrally acting adrenergic inhibitors decrease the (?) of both α1 and α2 receptors.

vasodilation

The net effect is to decrease heart rate and contractility by decreasing release of norepinephrine at α1 receptors and to promote (?) by decreasing norepinephrine release at α1 receptors at vascular smooth muscle.

clonidine (Catapres)

The prototype medication in this category is (?).

drowsiness

Although it does have some side effects—notably, (?) and dry mouth—clonidine is a relatively safe and frequently prescribed antihypertensive agent.

Methyldopa (Aldomet)

(?) is another centrally acting antihypertensive with a mechanism similar to clonidine.

peripheral adrenergic neuron blocking agents

Like the centrally acting adrenergic inhibitors, (?) work indirectly to decrease stimulation of adrenergic receptors.

norepinephrine

They do this by decreasing the amount of (?) released from sympathetic presynaptic terminals.

no longer commonly used

These agents are (?).

reserpine (Serpalan)

The prototype of this class is (?), which has two actions that decrease the amount of norepinephrine released.

synthesis of norepinephrine

First, it decreases the (?).

monoamine oxidase

Second, it exposes norepinephrine in the terminal vesicles to (?), an enzyme that destroys it.

peripheral vasodilation

This decreases stimulation of α1 receptors, resulting in (?), and of β1 receptors, resulting in decreased heart rate and contractility.

blood pressure

The decreased peripheral vascular resistance and cardiac output in turn lower (?).

serotonin

Reserpine also decreases synthesis of several CNS neurotransmitters (? and other catecholamines).

depression

This causes reserpine’s primary adverse effect, (?).

not frequently used

Reserpine, therefore, is (?) as an antihypertensive.

gastrointestinal cramps

Additional side effects include (?) and increased stomach acid production.

guanethidine (Ismeline)

Other medications with similar actions include (?) and guanadrel (Hylorel).

α1 receptor antagonists

This chapter’s section on medications affecting the sympathetic nervous system discusses the (?) in detail.

specific action

Only their (?) is repeated here.

prazosin (Minipress)

The prototype selective α1 antagonist is (?).

peripheral vascular resistance

It decreases blood pressure by competitively blocking the alpha 1 receptors, thereby inhibiting the sympathetically mediated increases in (?).

afterload

By causing the arterioles to dilate, prazosin directly decreases (?).

venous pooling

By causing the venules to dilate, it promotes (?), which decreases preload.

preload

The decreased afterload and (?) help to lower blood pressure.

Terazosin (Hytrin)

(?) is another medication with similar properties.

Labetalol (Normodyne)

Labetalol (Normodyne) and carvedilol (Coreg) competitively bind with both α1 and β1 receptors, increasing their antihypertensive actions.

β1-mediated vasoconstriction

Hypertension is treated by decreasing (?), which, again, decreases both preload and afterload.

heart rate

Beta 1 blockade decreases (?), contractility, and renin release from kidneys.

peripheral vascular resistance

By blocking the release of renin, which promotes vasoconstriction, these agents decrease (?) even further.

Labetalol

Labetalol is commonly used to treat hypertensive crisis and is rapidly replacing the use of sublingual nifedipine (Procardia) for this purpose.