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.