Pharmacology Chapter on Parasympathomimetics
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Questions and Answers

Which of the following terms describes a drug that acts on muscarinic acetylcholine receptors?

  • Parasympatholytic
  • Nicotinic
  • Muscarinic (correct)
  • Cholinergic

    • What is the term for a drug that directly binds to and activates a receptor to cause an agonist effect?

  • Parasympatholytic
  • Miotic
  • Indirect agonist
  • Direct agonist (correct)

    • What is the term for a drug that causes constriction of the pupil?

  • Mydriatic
  • Nicotinic
  • Muscarinic
  • Miotic (correct)

    • Which of the following is NOT a definition found in the provided text?

    <p>A drug that increases the synthesis of acetylcholine in the synapse (C)</p> Signup and view all the answers

    Which of the following correctly describes the term "cholinergic"?

    <p>A drug that relates to the effects of acetylcholine on receptors (C)</p> Signup and view all the answers

    What is the primary function of a parasympathomimetic drug?

    <p>To mimic the effects of the parasympathetic nervous system. (C)</p> Signup and view all the answers

    Which of the following is NOT a direct effect of parasympathetic stimulation on the cardiovascular system?

    <p>Increased blood pressure. (B)</p> Signup and view all the answers

    What is the primary mechanism by which parasympathomimetic drugs directly affect the visual system?

    <p>Activation of M3 receptors and subsequent increase in intracellular calcium. (C)</p> Signup and view all the answers

    What is the primary effect of parasympathetic stimulation on the respiratory system?

    <p>Decreased airflow. (B)</p> Signup and view all the answers

    Which of the following is NOT a known effect of parasympathetic stimulation on the gastrointestinal system?

    <p>Decreased intestinal peristalsis. (D)</p> Signup and view all the answers

    What is the primary function of botulinum toxin in relation to cholinergic transmission?

    <p>Blocking release of acetylcholine from the presynaptic terminal. (A)</p> Signup and view all the answers

    Which of the following drugs is NOT typically used in the treatment of myasthenia gravis?

    <p>Physostigmine. (A)</p> Signup and view all the answers

    What is the primary mechanism by which reversible acetylcholine esterase inhibitors exert their effects?

    <p>Preventing the breakdown of acetylcholine in the synaptic cleft. (C)</p> Signup and view all the answers

    Which of the following is a potential side effect associated with BOTH direct and indirect muscarinic agonists?

    <p>Nausea and vomiting. (B)</p> Signup and view all the answers

    Why are semi-synthetic derivatives of atropine, like ipratropium and tiotropium, preferred for treating asthma and COPD over atropine itself?

    <p>They have a lower risk of causing CNS side effects. (A)</p> Signup and view all the answers

    Which of the following is NOT a typical therapeutic application of muscarinic antagonists (parasympatholytics)?

    <p>Treatment of Parkinson's disease. (C)</p> Signup and view all the answers

    Which of the following statements BEST describes the primary mode of action of nicotinic antagonists in the context of surgery?

    <p>They prevent acetylcholine from binding to nicotinic receptors, leading to muscle relaxation. (A)</p> Signup and view all the answers

    What is the primary difference between reversible and irreversible acetylcholine esterase inhibitors?

    <p>Reversible inhibitors have a shorter duration of action. (C)</p> Signup and view all the answers

    Which of the following drugs is NOT directly involved in the treatment of cholinergic poisoning, whether by insecticides or warfare agents?

    <p>Physostigmine. (D)</p> Signup and view all the answers

    What distinguishes the pharmacological effects of parasympathomimetics on the cardiovascular system from those of parasympatholytics?

    <p>Parasympathomimetics decrease heart rate, while parasympatholytics increase heart rate. (B)</p> Signup and view all the answers

    Flashcards

    Cholinergic

    Pertaining to effects of acetylcholine on nicotinic and muscarinic receptors.

    Parasympatholytic

    A drug that competitively inhibits the action of acetylcholine at its receptors.

    Direct agonist

    Directly binds to and activates the receptor to cause the agonist effect.

    Indirect agonist

    Activates a receptor by increasing the synaptic concentration of the neurotransmitter.

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    Miotic

    A drug that causes constriction of the pupil; opposite of mydriatic.

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    Parasympathomimetic

    A drug that simulates the parasympathetic nervous system's activity.

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    Cholinergic Agonists

    Drugs that activate cholinergic receptors directly or indirectly.

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    Direct Action

    Binding and activating cholinergic receptors directly.

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    Indirect Action

    Prolonging acetylcholine's action by inhibiting its degradation.

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    M2 Receptors

    Cholinergic receptors that decrease heart rate.

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    M3 Receptors

    Cholinergic receptors involved in smooth muscle contraction.

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    Muscarinic Antagonists

    Drugs that block muscarinic receptors, reversing parasympathetic effects.

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    Nicotinic Receptors

    Cholinergic receptors that are ion channels, found at synapses.

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    Reversible AChE Inhibitors

    Drugs that inhibit acetylcholinesterase reversibly for therapeutic effects.

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    Irreversible AChE Inhibitors

    Agents that permanently inhibit acetylcholinesterase, causing toxicity.

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    Side Effects of Muscarinic Agonists

    Peripheral and CNS-related effects like bradycardia and sweating.

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    Neuromuscular Blocking Agents

    Drugs that inhibit muscle contraction, either depolarizing or non-depolarizing.

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    Parasympatholytic Effects

    Effects caused by blocking the parasympathetic nervous system.

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    Therapeutic Uses of AChE Inhibitors

    Improvement in conditions like Myasthenia gravis and Alzheimer's.

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    Hot as a hare

    A mnemonic for parasympatholytic effects: increased body temperature.

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    Study Notes

    Pharmacology of Cholinergic Agonists & Antagonists

    • Cholinergic: Relating to the effects of acetylcholine on nicotinic and muscarinic receptors.
    • Parasympatholytic: A drug that competitively inhibits acetylcholine action at its receptors.
    • Direct agonist: Directly binds to and activates the receptor, causing the agonist effect.
    • Indirect agonist: Brings about receptor activation by binding to another molecule (e.g., reuptake carrier or enzyme), increasing the synaptic neurotransmitter concentration.
    • Miotic: A drug that causes pupil constriction; opposite of mydriatic.
    • Muscarinic: Drugs that act on muscarinic acetylcholine receptors.
    • Nicotinic: Drugs that act on nicotinic acetylcholine receptors.
    • Parasympathomimetic: A drug that mimics parasympathetic nervous system (PNS) stimulation.

    Parasympathomimetic Drugs/Cholinergic Agonists - Spectrum of Action

    • Cholinoceptor Stimulants:
      • Pilocarpine (Alkaloids): Direct-acting drug affecting heart, smooth muscle, glands, and endothelium.
      • Physostigmine ("Reversible"): Direct-acting drug, indirectly affecting receptor stimulation.
      • Carbachol (Choline esters): Direct-acting drug affecting neuromuscular end plates and skeletal muscles.
      • Echothiophate ("Irreversible"): Indirect-acting drug, affecting receptor stimulation. (Note the difference between "reversible" and "irreversible" classifications)

    Organ System Effect - Comparison: Sympathetic & Parasympathetic ANS

    • Parasympathetic Division:
      • Neurotransmitter: Acetylcholine (pre and postganglionic)
      • Pre/postganglionic ratio: 1:1
      • Receptors: Nicotinic (ganglia), Muscarinic (effectors)
    • Sympathetic Division:
      • Neurotransmitter: Acetylcholine (preganglionic), Norepinephrine (postganglionic, except sweat glands)
      • Pre/postganglionic ratio: 1:20
      • Receptors: Nicotinic (ganglia), Adrenergic (effectors)

    Parasympathetic System Effects

    • "Rest and digest" principles:
      • Reduction of heart rate and blood pressure.
      • Bronchiole constriction
      • Miosis
      • Vasodilation
      • Increased GI motility
      • Decreased bladder sphincter tone

    Direct, Indirect, and Mixed Modes of Action for Parasympathomimetic Drugs

    • Direct: Bind and activate cholinergic receptors directly
    • Indirect: Prolong acetylcholine action by inhibiting degradation.
    • Mixed: Drugs that act both directly and indirectly.

    Organ System Effect - Receptor Specificity

    • Table 7-1 (receptor types and characteristics of cholinoceptors) shows locations, structural features, and post-receptor mechanisms for each receptor type (M1, M2, M3, M4, M5, NM, NN).

    Actions of Direct & Indirect Parasympathomimetics

    • Direct parasympathomimetics mimic acetylcholine's actions.
    • Indirect parasympathomimetics inhibit the breakdown of acetylcholine.
    • Drugs like physostigmine, rivastigmine, and tacrine work through this indirect action.

    Effects of Parasympathomimetics on Different Organ Systems

    • Detailed descriptions of M3 receptor effects on eye, salivary, gastric, pancreatic, and bowel functioning, impacting various organs including the eyes, glands, heart, blood vessels, and bladder.

    Cardiovascular System Effects

    • Blood vessels: Vasodilation indirectly through NO release (secondary messenger pathway & Ca2+ activation).
    • Heart (M2 receptors): Activation of K+ current, leading to decreased L-type Ca2+ channels, negative chronotropic and inotropic effects, inhibiting NE & Epi release, and decreased heart rate.
    • Conduction velocity of the SA node is decreased, hyperpolarizing atrial cells.

    Visual System Effects

    • Eye (M3 receptors): Activates secondary messengers (IP3, increased phospholipase C activity), opening Ca2+ channels, which increases intracellular Ca2+ concentrations, and increasing muscle tone.

    Respiratory System Effects

    • Respiratory tract (M3 receptors): Similar second messenger cascade as the visual system; constriction of smooth muscles in bronchioles/bronchi due to increased cytosolic Ca2+ levels, and increased bronchial secretion.

    Gastrointestinal, Glandular & Genitourinary Effects

    • Gastrointestinal: M2 & M3 increase motility and tone. M3 decreases sphincter contraction, increasing gastric, pancreatic, salivary, and intestinal fluid secretion.
    • Genitourinary system: M3 increases detrusor contraction and relaxes trigone and sphincter. In males, M3 affects erection.

    Central Nervous System Effects

    • Diverse functions, varying significantly with ability to pass the BBB. All preganglionic nerve transmission is cholinergic using acetylcholine.
    • Regulation of cortical excitability, memory and learning (Alzheimer's), pain processing, and brainstem motor control (Parkinson's)

    Cholinergic Nerve Transmission

    • Detailed diagrams and explanations of the cholinergic nerve transmission process, including synthesis, storage, release, and degradation of acetylcholine, and the involvement of enzymes like AChE.

    Dominant Effects of Cholinergic Drugs

    • Blood vessels: Indirect vasodilation through M3 receptors and nitric oxide.
    • Heart: Negative chronotropic and inotropic effects from M2 receptors.
    • Bronchial smooth muscle: Smooth muscle contraction from M3 receptors.
    • Gastrointestinal and endocrine: Increased secretion through M3 receptors.
    • CNS: Varied effects based on specific receptors affected.

    Muscarinic and Nicotinic Receptors

    • Muscarinic: All are GPCRs, slower activation, but prolonged effect. Includes M1, M2, M3, M4, and M5, with M1-3 being peripheral and M4-5 being CNS specific.
    • Nicotinic: All are ion channels, consisting of 5 subdomains (α, β, γ, δ, and ɛ). Found on all presynaptic autonomic ganglia and adrenal medulla, and skeletal muscle.

    Potential Drug Targets for Cholinergic Nerve Transmission

    • Describes various targets for drugs affecting cholinergic nerve transmission, including synthesis, storage, release, and degradation. Includes specific examples

    Synthesis of Acetylcholine

    • Describes inhibitors of acetylcholine synthesis, like hemicholinum and its effects relating to breakdown and reuptake of choline.

    Storage of Acetylcholine

    • Explains decreased storage and release of acetylcholine by vesamicol.

    Release of Stored Acetylcholine

    • Inhibits acetylcholine release through botulinum toxin (and its uses & mechanism).

    Reversible Acetylcholine Esterase Inhibitors

    • Describes pharmacological effects including stimulation then depression/paralysis of autonomic ganglia and skeletal muscles (nicotinic effects) and cholinergic receptors in the CNS

    Indirect Cholinergic Agents

    • Discusses the therapeutic use of reversible acetylcholine esterase inhibitors, like neostigmine and pyridostigmine, for diseases like myasthenia gravis and open-angle glaucoma and other conditions, their mechanism & potential side effects

    Irreversible Acetylcholine Esterase Inhibitors - Toxicity

    • Discusses toxicity from irreversible inhibitors including organophosphates such as pesticides and warfare agents and their long-term effects.

    Irreversible Acetylcholine Esterase Inhibitors—Treatment of Poisoned Patient

    • Provides guidelines for managing poisonings related to irreversible inhibitors.

    Cholinergic Antagonists (Parasympatholytics)

    • Categorizes antagonists by muscarinic and nicotinic types. Includes examples in each category for specific organs addressed.

    Muscarinic Antagonists

    • Discusses categorized antagonists focusing on their CNS and peripheral, competitive effects on organs like heart, circulation, respiratory system, eye, GI, and genitourinary tract including their clinical applications.

    Muscarinic Antagonists - Clinical Applications

    • Asthma and COPD. Overactive bladder. Peptic ulcers. Motion sickness.

    Parasympatholytics - Mnemonic

    • Provides a memory device for common side effects.

    Nicotinic Antagonists

    • Details depolarizing and non-depolarizing neuromuscular blocking agents, along with their mechanisms, therapeutic uses, and side effects.

    Nicotinic Antagonists at the Neuromuscular Junction

    • Discusses effects of both types of neuromuscular blocking agents, their mechanisms, and the table 11-4 comparing results.

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    Description

    Test your knowledge on parasympathomimetic drugs and their effects on the body. This quiz covers key terms, mechanisms, and effects associated with drugs that act on muscarinic acetylcholine receptors. Challenge yourself with questions on definitions and physiological impacts!

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