A parasympatholytic agent is a substance or activity that reduces the activity of the
parasympathetic nervous system
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...
.
(The parasympathetic nervous system is often colloquially described as the "Feed and Breed" or "Rest and Digest" portion of the
autonomic nervous system
The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...
. 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
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffla ...
, although some
poison
Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
s act to block the parasympathetic nervous system as well. Most drugs with parasympatholytic properties are
anticholinergics.
"Parasympatholytic" and
sympathomimetic
Sympathomimetic drugs (also known as adrenergic drugs and adrenergic amines) are stimulant compounds which mimic the effects of endogenous agonists of the sympathetic nervous system. Examples of sympathomimetic effects include increases in hea ...
agents have similar but not identical effects. For example, both cause
mydriasis
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drugs.
Normally, as ...
, but parasympatholytics reduce
accommodation (
cycloplegia), whereas sympathomimetics do not.
Clinical significance
Parasympatholytic drugs are sometimes used to treat slow heart rhythms (
bradycardia
Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...
s or
bradydysrhythmias) caused by
myocardial infarctions or other pathologies, as well as to treat conditions that cause
bronchioles in the lung to constrict, such as
asthma. 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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