Lec 3 Pharmacodynamic د.رياض
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Questions and Answers

What is the term used to describe a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it?

  • Agonist (correct)
  • Second messenger
  • Signal detector
  • Effector molecule

    • What is the characteristic of G proteinlinked and enzyme-linked receptors?

  • Amplified signal intensity and duration (correct)
  • No signal amplification
  • Reduced signal intensity
  • Signal suppression

    • What percentage of insulin receptors are spare?

  • 50%
  • 99% (correct)
  • 0.1%
  • 20%

    • What is the term used to describe systems that exhibit signal amplification?

    <p>Spare systems</p> Signup and view all the answers

    What is the percentage of adrenoceptors in the heart that are spare?

    <p>5-10%</p> Signup and view all the answers

    What is the result of signal amplification in G proteinlinked and enzyme-linked receptors?

    <p>Increased signal intensity and duration</p> Signup and view all the answers

    What is the primary function of receptors in the context of drug signaling?

    <p>To detect and respond to signals</p> Signup and view all the answers

    Which of the following best describes the relationship between agonist binding and cellular response?

    <p>A indirect response mediated by a cascade of events</p> Signup and view all the answers

    What is the functional significance of spare receptors in a system?

    <p>They provide an immense functional reserve, ensuring an adequate response</p> Signup and view all the answers

    Which type of receptors are characterized by signal amplification and spare receptors?

    <p>G protein-linked and enzyme-linked receptors</p> Signup and view all the answers

    What is the consequence of signal amplification in G protein-linked and enzyme-linked receptors?

    <p>A maximal response with only a fraction of receptors occupied</p> Signup and view all the answers

    What is the significance of the percentage of spare receptors in a system?

    <p>It reflects the functional reserve of the system</p> Signup and view all the answers

    What is the effect of upregulation of β adrenoreceptors?

    <p>Increased response to agonists</p> Signup and view all the answers

    What happens to the number of receptors in response to long-term administration of an agonist?

    <p>The number of receptors decreases</p> Signup and view all the answers

    What is the consequence of spare receptors in a system?

    <p>Increased sensitivity to agonists</p> Signup and view all the answers

    What is the result of signal amplification in G protein–linked and enzyme-linked receptors?

    <p>An increase in signal intensity and duration</p> Signup and view all the answers

    What is the effect of abrupt cessation of beta-blockers?

    <p>Rebound hypertension</p> Signup and view all the answers

    What is the relationship between spare receptors and maximal response?

    <p>A percentage of receptors remain unoccupied at maximal response</p> Signup and view all the answers

    What is the effect of long-term administration of an antagonist on receptors?

    <p>Upregulation of receptors</p> Signup and view all the answers

    What is the significance of spare receptors in the heart?

    <p>Provides a small functional reserve</p> Signup and view all the answers

    What is the effect of signal amplification on agonist binding?

    <p>Increases the potency of agonists</p> Signup and view all the answers

    What is the effect of desensitization of receptors?

    <p>Decreases the response to agonists</p> Signup and view all the answers

    What is the term used to describe a physicochemical alteration in the receptor which makes it unresponsive to the drug?

    <p>Tachyphylaxis</p> Signup and view all the answers

    What is the measure of the amount of drug necessary to produce an effect of a given magnitude?

    <p>Potency</p> Signup and view all the answers

    What is the formula used to calculate the therapeutic index?

    <p>TI = TD50 / ED50</p> Signup and view all the answers

    What type of antagonism is based on the physical property of drugs?

    <p>Physical antagonism</p> Signup and view all the answers

    What type of antagonism is characterized by the binding of an antagonist to a site on the enzyme rather than the agonist site?

    <p>Non-competitive antagonism</p> Signup and view all the answers

    What is the term used to describe the type of antagonism that occurs when opposite effects of two drugs on two different types of receptors antagonize each other?

    <p>Physiological antagonism</p> Signup and view all the answers

    What is the term used to describe the type of antagonism that occurs when an antagonist binds to another site on the receptor?

    <p>Allosteric antagonism</p> Signup and view all the answers

    Which of the following drugs is an example of a drug with a narrow therapeutic index?

    <p>Warfarin</p> Signup and view all the answers

    What is the result of increasing the concentration of a drug agonist in the presence of a competitive antagonist?

    <p>The antagonism is abolished</p> Signup and view all the answers

    What is the term used to describe the type of antagonism that occurs when an antagonist increases the metabolism and excretion of a drug?

    <p>Pharmacokinetic antagonism</p> Signup and view all the answers

    Study Notes

    Receptors and Signal Transduction

    • Drugs act as signals, and their receptors act as signal detectors.
    • Agonist refers to a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it.

    Signal Amplification

    • G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
    • Only a fraction of the total receptors for a specific ligand may need to be occupied to elicit a maximal response in systems with spare receptors.
    • Spare receptors provide an immense functional reserve, ensuring adequate response.
    • Example: Insulin receptors - about 99% are spare, ensuring adequate glucose entry into the cell.
    • Example: β adrenoceptors in the heart - only about 5% to 10% are spare.

    Receptors and Signal Transduction

    • Drugs act as signals, and their receptors act as signal detectors.
    • Agonist refers to a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it.

    Signal Amplification

    • G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
    • Only a fraction of the total receptors for a specific ligand may need to be occupied to elicit a maximal response in systems with spare receptors.
    • Spare receptors provide an immense functional reserve, ensuring adequate response.
    • Example: Insulin receptors - about 99% are spare, ensuring adequate glucose entry into the cell.
    • Example: β adrenoceptors in the heart - only about 5% to 10% are spare.

    Signal Amplification

    • G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
    • This amplification allows for a maximal response with only a fraction of the total receptors occupied, resulting in spare receptors.
    • Spare receptors provide a functional reserve, ensuring adequate responses to ligands.
    • For example, 99% of insulin receptors are spare, while only 5-10% of β adrenoceptors in the heart are spare.

    Upregulation and Downregulation of Receptors

    • Upregulation occurs when receptor activity is lower than usual, resulting in an increase in the number of receptors.
    • Example: long-term administration of beta-blockers upregulates β adrenoreceptors, leading to rebound hypertension when stopped.
    • Downregulation occurs due to repeated or long-term administration of an agonist, resulting in a decrease in the number of receptors.
    • Desensitization of the receptor to the drug may also occur, making it unresponsive to the drug (tachyphylaxis).

    Dose–Response Relationships

    • Graded dose–response relationships occur when the concentration of a drug increases, resulting in a gradual increase in pharmacologic effect.
    • Plotting the magnitude of response against increasing doses of a drug produces a graded dose–response curve shaped like a rectangular hyperbola.
    • Potency is a measure of the amount of drug necessary to produce an effect of a given magnitude, often measured as EC50 (the concentration producing 50% of the maximum effect).
    • Efficacy is the magnitude of response a drug causes when it interacts with a receptor.

    Therapeutic Index

    • The therapeutic index (TI) is calculated as TI = TD50 / ED50.
    • A narrow therapeutic index indicates a small difference between the dose producing the desired effect and the dose producing toxicity.
    • Examples: warfarin (narrow therapeutic index) and penicillin (wide therapeutic index).

    Drugs Antagonism

    • Pharmacological antagonists:
      • Competitive: antagonists compete with agonists at the same receptor site, and can be overcome by increasing the concentration of the drug agonist.
      • Non-competitive: antagonists bind irreversibly to a site on the enzyme, and cannot be overcome by increasing the concentration of the drug agonist.
    • Physical antagonism: based on physical properties of drugs, such as adsorption (e.g., charcoal in alkaloidal poisoning).
    • Chemical antagonism: based on drug-drug interaction, such as neutralization (e.g., NaHCO3 + HCl in hyperacidity).
    • Physiological/Functional Antagonism: opposite effects of two drugs on different types of receptors, such as histamine and adrenaline.
    • Pharmacokinetic antagonism: increasing the metabolism and excretion of a drug, such as enzyme induction.
    • Allosteric antagonism: antagonist binds to another site on the receptor, such as verapamil on Ca++ receptors.

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    Description

    A short quiz on biology, covering receptors, signal transduction, and agonist binding. Questions are based on the principles of signal amplification and cellular responses.

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