Cholinergic agonists are the name given to a group of medicines that mimic the actions of acetylcholine. Acetylcholine is one of the most common neurotransmitters in our body, and it has actions in both the central and peripheral nervous systems.
The peripheral nervous system consists of the autonomic nervous system (which regulates involuntary processes including digestion and breathing) and the somatic nervous system, which transmits signals from the central nervous system and external stimuli to skeletal muscle and also mediates hearing, sight, and touch. The autonomic nervous system can be further broken down into the sympathetic and parasympathetic nervous systems. The parasympathetic nervous system regulates various organ and gland functions at rest, including digestion, defecation, lacrimation, salivation, and urination, and primarily uses acetylcholine as its main neurotransmitter.
In medicine, the use of cholinergic agonists is limited because of their propensity to cause adverse effects in any organ under the control of the parasympathetic nervous system; adverse effects include blurred vision, cramps and diarrhea, low blood pressure and decreased heart rate, nausea and vomiting, salivation and sweating, shortness of breath, and increased urinary frequency. Currently, cholinergic agonists are only used to increase salivation in patients who suffer from a severely dry mouth, caused by radiation therapy or medical conditions such as Sjogren's syndrome.
