Agonistas Colinérgicos (Diretos/Muscarínicos) | Aula 10 | Farmacologia rápida e fácil | Flavonoide

Summary

This video lecture focuses on cholinergic agonists, which are drugs that interact with receptors in the parasympathetic nervous system. The instructor explains the difference between direct and indirect cholinergic agonists, providing insights into their effects and mechanisms. Direct agonists mimic acetylcholine at muscarinic receptors, influencing functions like heart rate and pupil size, while indirect agonists increase acetylcholine levels by inhibiting acetylcholinesterase. The lecture covers specific drugs such as metacholine, betacol, and pilocarpine, exploring their clinical uses, mechanisms, and potential side effects, particularly for conditions like glaucoma and urinary retention. The importance of understanding receptor selectivity and the clinical implications of these drugs is emphasized throughout.

Takeaways

• 😀 Cholinergic agonists mimic the actions of acetylcholine (ACh) in the body, affecting the parasympathetic nervous system.
• 😀 There are two types of cholinergic agonists: direct and indirect agonists.
• 😀 Direct agonists bind to cholinergic receptors (mostly muscarinic), while indirect agonists increase acetylcholine levels by inhibiting acetylcholinesterase.
• 😀 Metacholine is used to diagnose asthma and is more resistant to degradation by acetylcholinesterase than acetylcholine.
• 😀 Betacol is a muscarinic agonist used to treat urinary retention and improve gastrointestinal motility.
• 😀 Carbacol has some affinity for nicotinic receptors and is used topically in glaucoma treatment to decrease intraocular pressure.
• 😀 Pilocarpine is a natural alkaloid used for glaucoma treatment and increasing salivation in cases of xerostomia.
• 😀 Agonists at muscarinic receptors lead to parasympathetic effects like bradycardia, miosis (pupil constriction), and increased glandular secretions.
• 😀 Adverse effects of cholinergic agonists include bradycardia, hypotension, bronchoconstriction, and increased gastric acid secretion.
• 😀 Contraindications for cholinergic agonists include asthma, ulcers, low blood pressure, and coronary insufficiency.

Q & A

What are cholinergic agonists, and how do they work?

Cholinergic agonists are drugs that mimic the action of acetylcholine in the body. They act on cholinergic receptors, specifically muscarinic and nicotinic receptors, to produce parasympathetic effects, such as slowing the heart rate or constricting the pupils.

What is the difference between direct and indirect cholinergic agonists?

Direct cholinergic agonists bind directly to cholinergic receptors to produce a response, while indirect agonists inhibit acetylcholinesterase, the enzyme that breaks down acetylcholine, leading to an increased concentration of acetylcholine which then binds to receptors.

Why is acetylcholine not used clinically as a drug despite being an essential neurotransmitter?

Acetylcholine is not used clinically because it is rapidly broken down by acetylcholinesterase enzymes in the body, leading to unpredictable and widespread effects. Additionally, it interacts with both muscarinic and nicotinic receptors, making its effects difficult to control.

What are some examples of direct cholinergic agonists and their uses?

Examples include metacholine, which is used for asthma diagnosis, and bethanechol, which is used to treat urinary retention and stimulate gastrointestinal motility by acting on muscarinic receptors.

What is the advantage of metacholine over acetylcholine?

Metacholine is more resistant to breakdown by acetylcholinesterase than acetylcholine, allowing it to remain active in the body longer, though its effects are still somewhat unpredictable.

What is the primary clinical use of pilocarpine?

Pilocarpine is used primarily to treat glaucoma by reducing intraocular pressure and also for stimulating saliva production in patients with dry mouth conditions such as Sjögren's syndrome.

How does bethanechol help with urinary retention?

Bethanechol acts on muscarinic receptors in the bladder to stimulate the detrusor muscle, increasing contraction and helping to expel urine, making it useful for conditions like postoperative urinary retention or enlarged prostate.

Why is carbachol only used topically?

Carbachol is more likely to affect nicotinic receptors as well as muscarinic receptors, leading to unpredictable systemic effects. Therefore, it is used topically, such as in eye drops for glaucoma, to minimize systemic absorption.

What are the common side effects of cholinergic agonists?

Common side effects include hypotension (low blood pressure), bradycardia (slow heart rate), bronchoconstriction, excessive salivation, and sweating. These effects are typically due to overstimulation of cholinergic receptors.

What are the contraindications for using cholinergic agonists?

Cholinergic agonists should be avoided in patients with asthma, low gastric acid production, or hypotension, as these drugs can worsen conditions like bronchoconstriction, acid reflux, and further decrease blood pressure.