Let's learn about autonomic nervous system
drugs affecting the sympathetic nervous system.
The autonomic nervous system has 2 divisions.
The sympathetic division responds to stress
and activates the fight or flight response.
The parasympathetic division activates the
rest and digest response during non-stressful
conditions.
The sympathetic nervous system dilates the
pupils, speeds up the heart rate, inhibits
the salivary glands and bladder, dilates the
bronchioles, inhibits the sex organs, inhibits
digestion, promotes the release of glucose
from the liver, and promotes the release of
norepinephrine and epinephrine from the adrenal
glands.
The parasympathetic nervous system has the
opposite effect on organs.
It works to constrict the pupils, slow down
heart rate, promote salivation, stimulate
the bladder, constrict the bronchioles, stimulate
the sex organs, promote digestion, and stimulate
the gallbladder to release bile.
Drugs affecting the autonomic nervous system
have 4 possible actions.
These include: stimulation of the sympathetic
nervous system, inhibition of the sympathetic
nervous system, stimulation of the parasympathetic
nervous system and inhibition of the parasympathetic
nervous system.
We will be focusing on drugs that affect the
sympathetic nervous system in this video.
Drugs that stimulate the sympathetic nervous
system are called sympathetic agonists or
sympathomimetics.
Sympathomimetics can either work directly
or indirectly.
For example, a drug can have a direct effect
by binding to and activating an adrenergic
receptor.
Examples include the catecholamines such as
epinephrine, norepinephrine and dopamine.
Other sympathomimetics can work indirectly
by promoting the release of norepinephrine
from pre-synaptic vesicles.
Some sympathomimetics block reuptake of norepinephrine.
Examples of sympathomimetics that work indirectly
include amphetamine and cocaine.
There are 4 types of adrenergic receptors:
alpha1, alpha 2, beta 1 and beta 2.
Drugs can affect one or more receptor types
and have different actions depending on the
receptor.
The therapeutic applications for drugs affecting
the alpha 1 receptors includes treatment of
hypotension, nasal congestion and dilation
of pupils.
Therapeutic applications of drugs affecting
alpha 2 receptors include treatment of hypertension.
Drugs affecting beta 1 receptors are useful
in treating heart failure, cardiac arrest
and shock.
Drugs affecting beta 2 receptors can be used
to treat asthma and premature contractions
of labor.
Some sympathomimetics like epinephrine are
non-selective and affect multiple receptors.
Epinephrine affects all 4 types of receptors
and is used to treat cardiac arrest and asthma.
Pseudophedrine (pseudofed) phenylephrine affects
alpha 2 and beta 2 receptors and is used as
a nasal decongestant.
Isoproterenol (Isuprel) affects the beta 1
and beta 2 receptors and works to increase
the heart rate, force of contraction and conduction.
Dobutamine affects the beta 1 receptors and
works to increase the heart rate and force
of contraction in heart failure and shock.
Albuterol affects the beta 2 receptors.
Beta 2 agonists affect all sympathetic organs
except the heart.
Albuterol inhibits smooth muscles as in bronchodilation
and can be used to treat asthma and COPD.
Drugs that inhibit the sympathetic nervous
system are called adrenergic antagonists or
sympatholytics.
Adrenergic antagonists block adrenergic receptors.
Alpha-adrenergic antagonists or alpha-blockers
promote vasodilation by inhibiting vasoconstriction.
Alpha blockers also promote pupil constriction.
Beta adrenergic antagonists or beta-blockers
can affect the beta 1, beta 2 or both types
of receptors.
Beta blockers are used to treat the cardiovascular
system.
They work to decrease heart rate and force
of contraction.
Non-selective beta blockers such as propranolol
block both types of receptors and can exhibit
more side effects than selective beta blockers
such as atenolol (Tenormin) which only block
beta 1 receptors.
Selective beta blockers are also known as
cardioselective because they produce less
side effects on non-cardiac tissue.
Beta blockers have many therapeutic uses including
treatment of high blood pressure, migraine
headaches, angina pectoris, dysrhythmias,
heart failure and narrow-angle glaucoma.
I hope you have learned something about sympathetic
nervous system drugs and see you next time.
