Cholinergic agonists act at the same site as the neurotransmitter acetylcholine (ACh) and increase the activity of the ACh receptor sites throughout the body. Because these sites are found extensively throughout the parasympathetic nervous system, their stimulation produces a response similar to what is seen when the parasympathetic system is activated. As a result, these drugs are often called parasympathomimetic because their action mimics the action of the parasympathetic nervous system. Because the action of these drugs cannot be limited to a specific site, their effects can be widespread throughout the body, and they are usually associated with many undesirable systemic effects.
Cholinergic agonists work either directly or indirectly. Direct-acting cholinergic agonists occupy receptor sites for ACh on the membranes of the effector cells of the postganglionic cholinergic nerves, causing increased stimulation of the cholinergic receptor. In contrast, indirect-acting cholinergic agonists cause increased stimulation of the ACh receptor sites by reacting with the enzyme acetylcholinesterase and preventing it from breaking down the ACh that was released from the nerve. These drugs produce their effects indirectly by producing an increase in the level of ACh in the synaptic cleft, leading to increased stimulation of the cholinergic receptor site
For children, they may be more susceptible to the adverse effects associated with the cholinergic agonists, including GI upset, diarrhea, increased salivation that could lead to choking, and loss of bowel and bladder control, a problem that could cause stress in the child. Children should be monitored closely if these agents are used and should receive appropriate supportive care.
Bethanechol is approved for the treatment of neurogenic bladder in children older than 8 years of age. Neostigmine and pyridostigmine are used in the control of myasthenia gravis and for reversal of neuromuscular junction blocker effects in children. Edrophonium is used for diagnosis of myasthenia gravis only.
For adults, they should be cautioned about the many adverse effects that can be anticipated when using a cholinergic agonist. Flushing, increased sweating, increased salivation and GI upset, and urinary urgency often occur. The patient also needs to be aware that dizziness, drowsiness, and blurred vision may occur and that driving and operating dangerous machinery should be avoided.
The cholinergic agonist should be used only in those situations in which the benefit to the mother is greater than the risk to the fetus or neonate. .
胆碱能激动剂只能在母亲好处大于胎儿或新生儿危险的情况下使用。
For older patients, they are more likely to experience the adverse effects associated with these drugs—CNS, cardiovascular, GI, respiratory, and urinary effects. Because older patients often have renal or hepatic impairment, they are also more likely to have toxic levels of the drug related to changes in metabolism and excretion.
The older patient should be started on lower doses of the drugs and should be monitored very closely for potentially serious arrhythmias or hypotension.
老年患者用药时应从小剂量开始，应严密监护是否出现可能会很严重节律失常或低血压。
★Vocabulary ★
cholinergic – n. a. 胆碱能的（药）
cholinergic agonist – 胆碱能激动剂
acetylcholine (ACh) – n. 乙酰胆碱
parasympathomimetic – a. n. 拟副交感神经的（药）
mimic – v. 模仿，拟
effector cell – 效应细胞
postganglionic – a. （神经）节后的
acetylcholinesterase – n. 乙酰胆碱酯酶
breaking down – 分解
synaptic cleft – 突触间隙
susceptible – a. 易受影响的，易感的
salivation – n. 流涎，唾液分泌
bethanechol – n. 氯贝胆碱
neurogenic – a. 神经源性
neostigmine – n. 新斯的明
pyridostigmine – n. 吡啶斯的明
myasthenia – n. 肌无力
myasthenia gravis – 重症肌无力
edrophonium – n. 依酚氯铵
★Video ★
Cholinergic Agonists
★Tests★
1. The following are true about cholinergic agonists, except:
A. These drugs exert their effect by mobilizing the acetylcholine into their receptors found throughout the body.
B. Some of their effects include vasodilation, bronchoconstriction, and bladder relaxation.
C. Ophthalmic agents can induce miosis or pupil constriction.
D. Edrophonium is used for diagnosis of myasthenia gravis only.
2. All of the following are direct-acting cholinergic agonists, except:
A. Pilocarpine
B. Neostigmine
C. Carbachol
D. Cevimeline
答案 Answers
1. A. These drugs exert their effect by mobilizing the acetylcholine into their receptors found throughout the body. Rationale: Cholinergic agonists act at the same site as the neurotransmitter acetylcholine (ACh) and increase the activity of the ACh receptor sites throughout the body. They do not mobilize acetylcholine into their receptors. 2. B. Neostigmine Rationale: It is an agent for myasthenia gravis and is therefore an indirect-acting cholinergic agonist.
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