The acetylcholine inhibitors are chemical compounds that compete with and counteract the working of the neurotransmitter acetylcholine. As a result, they dampen the activity of the parasympathetic nervous system. Effects of the acetylcholine inhibitors include decreasing gastrointestinal activity, increasing urinary retention, decreasing airway constriction, and speeding up the heart rate. Many of these clinical effects are helpful in treating a variety of diseases.
Acetylcholine inhibitors compete with the normal action of the neurotransmitter acetylcholine (ACh). Neurotransmitters are chemical compounds that transfer information from nerve cells to body tissues. They are released in response to an electrical signal from nerve cells, and bind to receptors either on cell surfaces or within cells. ACh plays a critical role in the central nervous system, which encompasses the brain and spinal cord, as well as in the peripheral nervous system.
This neurotransmitter is also important because it helps carry out the parasympathetic nervous system's activities. This system controls the automatic functions of the body during times of safety. It works opposite to the sympathetic nervous system, which is responsible for the “fight or flight” response seen in times of danger. Normal activity of the parasympathetic nervous system allows the body to “rest and digest,” and therefore promotes decreased heart rate, increased gastrointestinal activity, and narrowing of the pupils of the eyes.
By competing with the actions of ACh, acetylcholine inhibitors restrict the actions of the parasympathetic nervous system. Effects of these medications therefore alter some natural functions of the human body. They cause dilation of the pupils, increased heart rate, constipation, urinary retention, loss of perspiration, and dry mucus membranes.
The acetylcholine inhibitors have a broad range of clinical applications. They can be used to treat respiratory disorders such as asthma and chronic obstructive pulmonary disease because they decrease respiratory secretions and minimize airway spasms. Overactive bladder can be controlled by the anticholinergic agents because they promote the retention of urine. Slow heart rate, known as bradycardia, can also be treated with these medications.
Compounds that have acetylcholine inhibitor activity have been used for hundreds of years for a variety of purposes. The belladonna plant contains the chemical substance atropine, which is an acetylcholine inhibitor. Italian ladies once applied extracts of this plant to their eyes because it caused dilation of the pupils. They thought that doing this increased their physical attractiveness.
A wide range of acetylcholine inhibitors, also known as the anticholinergic agents, continue to have important functions. Atropine in a more refined form is still used in modern times. Other anticholinergic agents include ipratropium, scopolamine, oxybutynin, and tolterodine.