Nursing Pharmacology Chapter 18 Adrenergic Agonist and Adrenergic Blockers

Two groups of drugs that affect the sympathetic nervous system:

The adrenergic agonists (sympathomimetics or adrenomimetics) and the adrenergic blockers (sympatholytics or adrenolytics)

The alpha adrenergic receptors are located in the:

vasculature tissues (vessels) of muscle

When alpha 1 receptor is stimulated the:

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

Alpha 1

Increase force of heart contraction; vasoconstriction increases blood pressure; mydriasis (dilation of pupils) occurs; decreases secretion in salivary glands; increases urinary bladder relaxation and urinary sphincter contraction

Alpha 2

Inhibits the release of norepinephrine; dilates blood vessels; produces hypotension; decreases gastrointestinal motility and tone

Beta 1

Increases heart rate and force of contraction; increases renin secretion, which increases blood pressure

Beta 2

Dilates bronchioles; promotes gastrointestinal and uterine relaxation; promotes increase in blood sugar through glycogenolysis in liver; increases blood flow in skeletal muscles

Dopaminergic receptor can only be stimulated by

dopamine

When dopaminergic receptors are stimulated they cause

the vessels to dilate and the blood flow increases

Transmitters are inactivated by:

1. reuptake of the transmitter back into the neuron (nerve cell terminal). 2. enzymatic tranformation or degradation and 3. diffusion away from the receptor.

The two enzymes that inactivate the metabolism of norepinephrine are:

1. Monoamine oxidase (MAO) which is found inside the neuron; and 2. catechol-0-methyltransferase (COMT) which is found outside the neuron.

Drugs can stop the termination of the neurotransmitter by either:

1. inhibiting the norepinephrine reuptake which prolongs the action of the transmitter or 2. inhibiting the degradation of norepinephrine by enzyme action.

The sympathomimetic drugs that stimulate adrenergic receptors are classified into three categories according to their effects on organ cells:

1. direct acting sympathomimetics which directly stimulate the adrenergic receptor; 2. indirect acting sympathomimetics, which stimulate the release of norepinephrine from the terminal nerve endings; and 3. mixed acting sympathomimetics, both stimulate th

Catecholamines

are the chemical structures of a substance (either endogenous or synthetic) that can produce a sympathomimetic response

Noncatecholamines

stimulate the adrenergic receptors

Nonselective

excites all receptors approximately equally

Inotropic

strengthens myocardial contractions

Selective

excites a specific receptor

Adrenergic blockers

drugs that block the effects of the adrenergic neurotransmitter

Alpha blockers

drugs that block or inhibit a response at the alpha adrenergic receptor site

Beta blockers

drugs that block or inhibit a response at the beta receptors causing a decrease in heart rate and a decrease in blood pressure usually follows

Intrinsic sympathomimetic activity (ISA)

is the ability of certain beta blockers to bind with a receptor and exert limited or partial activation of the receptor while preventing strong agonists from binding to that receptor producing complete activation.

Adrenergic neuron blockers

drugs that block the release of norepinephrine from the sympathetic terminal neurons