A parasympatholytic agent is a substance or activity that reduces the activity of the
parasympathetic nervous system.
(The parasympathetic nervous system is often colloquially described as the "Feed and Breed" or "Rest and Digest" portion of the
autonomic nervous system. The parasympathetic nervous system becomes strongly engaged during or after a meal and during times when the body is at rest.)
The term parasympatholytic typically refers to the effect of a
drug, although some
poisons act to block the parasympathetic nervous system as well. Most drugs with parasympatholytic properties are
anticholinergic
Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system.
These agents inhibit the parasympathetic nervous sys ...
s.
"Parasympatholytic" and
sympathomimetic agents have similar but not identical effects. For example, both cause
mydriasis, but parasympatholytics reduce
accommodation (
cycloplegia
Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation. Because of the paralysis of the ciliary muscle, the curvature of the lens can no longer be adjusted to focus on nearby objects. This results in sim ...
), whereas sympathomimetics do not.
Clinical significance
Parasympatholytic drugs are sometimes used to treat slow heart rhythms (
bradycardias or
bradydysrhythmias) caused by
myocardial infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...
s or other pathologies, as well as to treat conditions that cause
bronchiole
The bronchioles or bronchioli (pronounced ''bron-kee-oh-lee'') are the smaller branches of the bronchial airways in the lower respiratory tract. They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start ...
s in the lung to constrict, such as
asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
. By blocking the parasympathetic nervous system, parasympatholytic drugs can increase heart rate in patients with bradycardic heart rhythms, and open up airways and reduce mucous production in patients with asthma.
About
External links
Overview at salisbury.edu*
Anticholinergics
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