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 autonomic nervous system is responsible for regulat ...

. The term parasympatholytic typically refers to the effect of a

drug A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via insufflation (medicine), inhalation, drug i ...

, although some

poison A poison is any chemical substance that is harmful or lethal to living organisms. 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 figurati ...

s 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 acetylcholine (ACh) neurotransmitter at synapses in the central nervous system, central and peripheral nervous system. These agents inhibit the parasympatheti ...

s. Parasympatholytic agents and sympathomimetic agents have similar effects to each other, although some differences between the two groups can be observed. For example, both cause

mydriasis Mydriasis is the Pupillary dilation, dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, Physical trauma, trauma, or the use of c ...

, 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 ...

), whereas sympathomimetics do not. __NOTOC__

Clinical significance

Parasympatholytic drugs are sometimes used to treat slow heart rhythms (

bradycardia Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due ...

s or

bradydysrhythmias Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due t ...

) caused by

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

s or other pathologies, as well as to treat conditions that cause

bronchiole The bronchioles ( ) 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 of the respiratory zone delivering air to ...

s in the lung to constrict, such as

asthma Asthma is a common 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 wh ...

. By blocking the parasympathetic nervous system, parasympatholytic drugs can increase heart rate in patients with bradycardic heart rhythms, and open up airways and reduce mucus production in patients with asthma.

References

External links

Overview at salisbury.edu
* Anticholinergics {{biochem-stub