cholinergic drug
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What is a cholinergic drug?
Cholinergic drugs either mimic, enhance, or inhibit the neurotransmitter acetylcholine. Acetylcholine is the primary transmitter of nerve impulses within the parasympathetic nervous system; this system slows the heart rate, dilates blood vessels, contracts smooth muscles, and increases bodily secretions.
Examples of cholinergic drugs include pilocarpine, which is used in eyedrops to treat glaucoma, and neostigmine and pyridostigmine, which are used to treat myasthenia gravis. Drugs such as atropine and scopolamine act as antagonists on muscarinic receptors and suppress the parasympathetic system's actions.
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How do cholinergic drugs affect the body?
Cholinergic drugs influence the neurotransmitter acetylcholine, which is vital to the parasympathetic nervous system. They can either mimic, enhance, or inhibit acetylcholine's actions, affecting bodily functions such as smooth muscle contraction, blood vessel dilation, bodily secretions, and heart rate.
Some cholinergic drugs, like pilocarpine, are used to treat conditions such as glaucoma by constricting the pupil and decreasing intraocular pressure. Others, such as atropine and scopolamine, suppress the parasympathetic system, leading to the drying of secretions, relaxation of smooth muscles, increased heart rate, and pupil dilation.
Certain inhibitors, like neostigmine and pyridostigmine, are used to treat myasthenia gravis by prolonging acetylcholine's action at the neuromuscular junction.
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Which chemical messenger do cholinergic drugs influence?
Cholinergic drugs primarily influence the chemical messenger acetylcholine, a neurotransmitter. These drugs can either mimic, enhance, or inhibit acetylcholine's actions, which is the primary transmitter of nerve impulses within the parasympathetic nervous system. By interacting with acetylcholine receptors, cholinergic drugs affect bodily functions such as smooth muscle contraction, blood vessel dilation, bodily secretions, and heart rate.
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What are some medical uses for cholinergic drugs?
Cholinergic drugs can inhibit, enhance, or mimic the neurotransmitter acetylcholine in the parasympathetic nervous system. They have various medical applications:
- Muscle Spasms/Sweating Botulinum toxin, a cholinergic drug, treats severe muscle spasms or uncontrollable sweating when locally injected.
- Glaucoma Pilocarpine, an acetylcholine-like drug, is used in eyedrops to constrict the pupil and decrease intraocular pressure in glaucoma.
- Anesthesia Atropine and scopolamine, muscarinic receptor antagonists, dry up secretions and dilate the bronchi during anesthesia and dilate pupils during ophthalmological procedures.
- Motion Sickness Scopolamine can treat motion sickness because it can depress the activity of the central nervous system.
- Myasthenia Gravis Acetylcholinesterase inhibitors such as neostigmine and pyridostigmine treat myasthenia gravis by prolonging acetylcholine action at the neuromuscular junction.
- Alzheimer's Disease Acetylcholinesterase inhibitors such as galantamine, donepezil, and rivastigmine can delay the progression of amnestic MCI.
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How do cholinergic drugs help treat diseases like Alzheimer's or glaucoma?
Cholinergic drugs affect the neurotransmitter acetylcholine, influencing the parasympathetic nervous system. In glaucoma, drugs like pilocarpine act as muscarinic-receptor agonists, constricting the pupil and reducing intraocular pressure.
For Alzheimer's, anticholinesterase drugs boost acetylcholine levels in the brain by preventing its breakdown. This can slow neuron degeneration and cognitive decline. Donepezil, tacrine, and galantamine are examples, but their use is limited due to potential side effects.
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What are some possible side effects of using cholinergic drugs?
Cholinergic drugs can have various side effects depending on their mechanism of action. Drugs like pilocarpine that mimic acetylcholine may cause decreased heart rate and increased activity in the gastrointestinal and urinary systems.
Drugs like atropine and scopolamine that block muscarinic receptors can lead to dry mouth, constipation, increased heart rate, blurred vision, and difficulty urinating.
Nicotinic-receptor antagonists may cause paralysis of the autonomic nervous system, resulting in blurred vision, constipation, impotence, and urinary retention.
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cholinergic drug, any of various drugs that inhibit, enhance, or mimic the action of the neurotransmitter acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous systemβi.e., that part of the autonomic nervous system that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows the heart rate.
Acetylcholine release by nerve impulses can be blocked by botulinum toxin, a very potent chemical that is produced in food contaminated by the bacteria Clostridium botulinum and is an occasional cause of severe food poisoning (botulism). The most serious effect is paralysis of the skeletal muscle. However, when botulinum toxin is locally injected, it can be used to treat severe muscle spasm or severe, uncontrollable sweating. Under such trade names as Botox, it is also used for cosmetic purposes; botulinum toxin injected locally will paralyze muscles of the face, thus relaxing the skin and reducing wrinkles.
Many drugs interact with acetylcholine receptors. Acetylcholine itself produces extremely short-lived effects because it is destroyed rapidly in the blood. One acetylcholine-like drug that is employed therapeutically is pilocarpine, a selective muscarinic-receptor agonist that is used in eyedrops to constrict the pupil and to decrease the intraocular pressure that is raised in the disease glaucoma.
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Antagonists acting on muscarinic receptors include such drugs as atropine and scopolamine. These drugs suppress all the actions of the parasympathetic system, which results in drying up of the secretions of the body (e.g., saliva, tears, sweat, bronchial secretions, and gastrointestinal secretions); relaxation of the smooth muscle in the intestine, bronchi, and urinary bladder; an increase in the heart rate; dilation of the pupils; and paralysis of ocular focusing. These drugs are widely used to dry up secretions and dilate the bronchi during anesthesia and to dilate the pupils during ophthalmological procedures. Scopolamine is also used to treat motion sickness, an effect that depends on its ability to depress the activity of the central nervous system.
Nicotine, the principal addictive ingredient in the tobacco used in cigarettes and cigars, exerts its actions at a subset of cholinergic receptors known as nicotinic receptors. Agents that block these receptors, so-called nicotinic-receptor antagonists, are divided into those that act mainly on skeletal muscle and those that act on ganglia cells. The latter group includes hexamethonium and trimethaphan. These drugs cause overall paralysis of the autonomic nervous system because they do not distinguish between sympathetic and parasympathetic ganglia and therefore are not specific in their action. They were the first effective agents to reduce high blood pressure (antihypertensive drugs), but they have many troublesome side effects associated with paralysis of the autonomic nervous system (e.g., blurred vision, constipation, impotence, inability to urinate). They have been replaced by more selective drugs. The nicotinic-receptor antagonists that act at the neuromuscular junction are used during surgical procedures to produce muscle relaxation.
Acetylcholine is inactivated by the enzyme acetylcholinesterase, which is located at cholinergic synapses and breaks down the acetylcholine molecule into choline and acetate. One group of acetylcholinesterase inhibitors (anticholinesterase drugs) is used to treat myasthenia gravis, a disorder characterized by muscle weakness. Neostigmine and pyridostigmine are drugs that can access the neuromuscular junction, but they cannot enter the ganglia of the autonomic nervous system and thus do not cross the blood-brain barrier. Therefore, these agents prolong the action of acetylcholine specifically at the neuromuscular junction.