Mechanisms of Receptor Antagonism
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Questions and Answers

What distinguishes a partial agonist from a full agonist?

  • Partial agonists do not bind to the same receptor sites as full agonists.
  • Partial agonists only block receptor activity.
  • Partial agonists evoke a response that is less than maximal. (correct)
  • Partial agonists produce a maximal response.

    • How do partial antagonists affect the response of full agonists?

  • They can only act independently of full agonists.
  • They have no effect on full agonists.
  • They enhance the response of full agonists.
  • They diminish the response of full agonists when administered prior. (correct)

    • What is the effect of inverse agonists on constitutively active receptors?

  • They enhance the activity of these receptors.
  • They inactivate these receptors, preventing basal activity. (correct)
  • They only bind to receptors in the presence of an agonist.
  • They maintain the receptors in an active state.

    • What happens when both a partial agonist and a full agonist bind to the same receptor site?

    <p>There is competition for binding, affecting the overall response.</p> Signup and view all the answers

    What is desensitization in receptor regulation?

    <p>A decrease in response to a drug after prolonged exposure.</p> Signup and view all the answers

    Which statement accurately describes competitive antagonism?

    <p>It can be overcome by increasing the concentration of agonists.</p> Signup and view all the answers

    How does allosteric modulation affect receptor activity?

    <p>It changes the receptor shape without directly competing with agonists.</p> Signup and view all the answers

    Which of the following best describes non-competitive antagonism?

    <p>It involves binding to different sites than the agonist.</p> Signup and view all the answers

    What type of antagonist binds irreversibly or pseudo-irreversibly to the same site as the agonist?

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

    Which mechanism leads to a rightward shift in the dose-response curve without affecting the agonist's maximal response?

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

    What is the primary characteristic of a physiological antagonist?

    <p>It produces effects through different receptor systems.</p> Signup and view all the answers

    How does an allosteric antagonist affect the response of an agonist?

    <p>It inhibits or potentiates the response through a different site.</p> Signup and view all the answers

    What is the main effect of a competitive antagonist on agonist concentration-response relationships?

    <p>It requires higher concentrations of agonist to achieve the same effect.</p> Signup and view all the answers

    Which of the following describes a situation of physiologic antagonism?

    <p>Acetylcholine cancels the effect of norepinephrine through different receptors.</p> Signup and view all the answers

    In receptor antagonism, what does the term 'spare receptors' refer to?

    <p>Receptors not engaged in the agonist-receptor interaction.</p> Signup and view all the answers

    What outcome is expected when allosteric modulation of a receptor occurs?

    <p>It can lead to either an increase or decrease in the response.</p> Signup and view all the answers

    What characteristic defines a competitive antagonist?

    <p>It can be displaced by an agonist.</p> Signup and view all the answers

    How does binding of a competitive antagonist affect the response curve of an agonist?

    <p>It shifts the curve to the right, increasing EC50.</p> Signup and view all the answers

    Which type of antagonist binds to a different site than the agonist on the receptor?

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

    In physiological antagonism, how does the antagonist exert its effect?

    <p>By acting through a different receptor mechanism.</p> Signup and view all the answers

    What is the primary nature of binding for a competitive antagonist?

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

    Which type of antagonist involves binding that cannot be dislodged by an agonist?

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

    How is the term 'spare receptors' defined in relation to receptor response?

    <p>They are functional but not necessary for maximum response.</p> Signup and view all the answers

    What characterizes an antagonist with allosteric modulation?

    <p>It alters receptor shape and function without competing for the binding site.</p> Signup and view all the answers

    Study Notes

    Mechanisms of Receptor Antagonism

    • Antagonists can bind irreversibly or pseudo-irreversibly to the same site as agonists, shifting the dose-response curve to the right and reducing the maximum response.
    • Allosteric effects occur when a ligand binds to a different site on the receptor, either inhibiting or potentiating the response, with effects saturating as the allosteric site fills.
    • Physiologic antagonism results from the alteration of an agonist’s effect due to the action of another drug acting on a different receptor system, not directly affecting the agonist-receptor interaction.
    • Example of physiological antagonism: Norepinephrine raises heart rate via β1 receptors, while acetylcholine reduces it through muscarinic receptors.

    Competitive Antagonism

    • Competitive antagonists bind reversibly to the receptor, allowing blockade to be overcome by increased agonist concentration.
    • Spare receptors can influence this process, as they remain functional even without being bound.
    • The agonist's maximal efficacy remains unchanged, although the response curve shifts to the right, parallel to the original curve.

    Partial Agonists/Antagonists

    • Partial agonists elicit a lesser response than full agonists, exhibiting competitive binding which decreases the efficacy of full agonist responses when administered together.
    • Partial agonists can inhibit full agonist effects due to competition at the same receptor site.

    Inverse Agonists

    • Inverse agonists reduce the activity of constitutively active receptors, pushing them into an inactive state and eliciting a response opposite to that of an agonist.
    • Contrary to prior beliefs, some receptors can remain active even without an agonist.

    Receptor Regulation

    • Receptor sensitivity changes can lead to desensitization, which reduces response to a drug over time.
    • Exposure to the drug may activate spare receptors, which are capable of contributing to maximum responses without necessarily binding agonists directly.

    Antagonist Characteristics

    • Antagonists possess affinity for receptors but lack intrinsic activity.
    • Competitive antagonists can be displaced by agonists, differentiating them from non-competitive antagonists.
    • Understanding the binding nature (reversible vs irreversibly, allosteric vs orthosteric) is crucial in characterizing antagonism.

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    Pharmacology - Introduction to Pharmacology and Pharmacodynamics - Pharmacodynamics Lecture PDF

    Description

    Explore the intricate mechanisms of receptor antagonism, including the effects of irreversible and pseudo-irreversible antagonists on dose-response curves. Understand how allosteric effects influence receptor function and pharmacodynamics. This quiz is essential for students in pharmacology and biochemistry.

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