pharm ch 15 adregenic agonist AND anatagonist

The four main receptors

The four main receptors

alpha₁, alpha₂, beta₁, and beta₂.

alpha-adrenergic receptors are located in

blood vessels, eyes, the bladder, and prostate

alpha₁ receptors in vascular tissues of muscles are

a.      stimulated, the arterioles and venules constrict, increasing peripheral resistance and blood return to the heart.

alpha₂ receptors are located in

the postganglionic sympathetic nerve endings.

akpha 2 receptors when stimulated

a.      inhibit the release of norepinephrine, leading to a decrease in vasoconstriction.

beta₁ receptors are located primarily

in the heart but are also found in the kidney

. Stimulation of the beta₁ receptors increases

myocardial contractility and heart rate.

beta₂ receptors are found mostly in the

smooth muscles of the lung and GI tract, the liver, and the uterine muscle.

beta 2 receptors

(1) relaxation of the smooth muscles of the lungs,

(2) a decrease in gastrointestinal tone and motility

(3) activation of glycogenolysis in the liver, and

(4) relaxation of the uterine muscle.

two enzymes that inactivate norepinephrine

(1)   monoamine oxidase (MAO), which is inside the neuron

(2) catechol-O-methyltransferase (COMT), which is outside the neuron.

Drugs can prolong the action of the neurotransmitter by either

(1) inhibiting reuptake

(2) inhibiting degradation by enzyme action.

 

Sympathomimetic drugs are classified into three categories according to their effects on organ cells.

(1) direct-acting sympathomimetics

(2) indirect-acting sympathomimetics

(3) mixed-acting sympathomimetics.

Catecholamines are

the chemical structures of a substance that can produce a sympathomimetic response. (epinephrine, norepinephrine, and dopamine)

Drugs that affect multiple adrenergic receptors are

nonselective

Drugs that affect a specific receptor are

selective

Alpha-blocking agents are divided into two groups:

(1)   selective alpha blockers that block alpha₁

(2)   nonselective alpha blockers that block alpha₁ and alpha₂.

Beta blockers decrease

heart rate, a decrease in blood pressure usually follows.

Some of the beta blockers are nonselective

(1)   , blocking both beta₁ and beta₂ receptors.

Not only does the heart rate decrease because of beta₁ blocking

(1)   , but bronchoconstriction also occurs.

Nonselective beta blockers block

(1)   both beta₁ and beta₂ and are contraindicated in asthma and should be used with extreme caution in any patient who has chronic obstructive pulmonary disease (COPD).

Beta blockers are useful in treating

(1)   mild to moderate hypertension, angina pectoris, and myocardial infarction.

Beta blockers should not be abruptly discontinued but rather should be

(1)   be tapered off over 1–2 weeks to avoid tachycardia, hypertension, severe angina, dysrhythmia, and MI.