Neurotransmission in Adrenergic Neurons
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Questions and Answers

What is the rate-limiting step in the formation of norepinephrine?

  • Decarboxylation of DOPA to dopamine
  • Hydroxylation of tyrosine to DOPA (correct)
  • Storage of dopamine in synaptic vesicles
  • Transport of tyrosine into the neuron

    • What happens to dopamine after its synthesis in the adrenergic neuron?

  • It is broken down into byproducts.
  • It is converted directly into norepinephrine.
  • It is released into the synaptic gap immediately.
  • It is transported into synaptic vesicles. (correct)

    • Which enzyme is responsible for converting tyrosine to DOPA?

  • Tyrosine hydroxylase (correct)
  • DOPA decarboxylase
  • Tyrosine decarboxylase
  • Aromatic l-amino acid decarboxylase

    • What is the role of reserpine in the context of adrenergic neurons?

    <p>Blocks the amine transporter system for dopamine</p> Signup and view all the answers

    Which of the following steps is NOT involved in neurotransmission at adrenergic neurons?

    <p>Elimination of electrical signals</p> Signup and view all the answers

    What percentage of norepinephrine is released by the adrenal medulla?

    <p>20%</p> Signup and view all the answers

    What triggers the release of norepinephrine from neurons?

    <p>An action potential arriving at the nerve junction</p> Signup and view all the answers

    What mechanism is utilized by norepinephrine to initiate intracellular events in the effector cell?

    <p>Cyclic adenosine monophosphate (cAMP) second messenger system</p> Signup and view all the answers

    Which drug can inhibit the release process of norepinephrine?

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

    What happens to norepinephrine after it is released into the synaptic space?

    <p>It diffuses out of the synaptic space and enters the general circulation</p> Signup and view all the answers

    What is the primary function of α2 receptors when stimulated?

    <p>Inhibit the release of norepinephrine</p> Signup and view all the answers

    How do α2 receptors affect intracellular cAMP levels?

    <p>Inhibit cAMP levels</p> Signup and view all the answers

    Which drug is a selective antagonist for α1A receptors?

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

    What distinguishes β receptors from α receptors in their response to drugs?

    <p>They respond strongly to isoproterenol with less sensitivity to epinephrine</p> Signup and view all the answers

    Which of the following α1 receptor subtypes is NOT part of the extended classification?

    <p>α1Z</p> Signup and view all the answers

    What is the primary mechanism for the termination of norepinephrine's effects?

    <p>Recapture by uptake system</p> Signup and view all the answers

    Which adrenergic receptor family shows a weak response to isoproterenol?

    <p>Both α1 and α2-adrenoceptors</p> Signup and view all the answers

    What is the rank order of potency for α adrenoceptors?

    <p>epinephrine &gt; norepinephrine &gt; isoproterenol</p> Signup and view all the answers

    What role does catechol-O-methyltransferase (COMT) play in norepinephrine metabolism?

    <p>It converts norepinephrine into inactive metabolites</p> Signup and view all the answers

    Which substances can inhibit the uptake of norepinephrine?

    <p>Cocaine and tricyclic antidepressants</p> Signup and view all the answers

    What effect is mediated by α1 adrenoceptors?

    <p>Increased closure of internal sphincter of the bladder</p> Signup and view all the answers

    Which of the following effects is primarily associated with β2 adrenoceptors?

    <p>Decreased peripheral resistance</p> Signup and view all the answers

    What is one mechanism suggested to explain receptor desensitization?

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

    What is the potency rank order for β receptors?

    <p>isoproterenol &gt; epinephrine &gt; norepinephrine</p> Signup and view all the answers

    What effect does β1 adrenoceptor activation primarily cause?

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

    Which of the following receptors primarily mediates responses in the heart?

    <p>β1 receptors</p> Signup and view all the answers

    What is the primary effect of stimulating α1 receptors?

    <p>Vasoconstriction in skin and abdominal viscera</p> Signup and view all the answers

    Which of the following does NOT describe the effects mediated by α2 adrenoceptors?

    <p>Increased insulin release</p> Signup and view all the answers

    Which β receptor subtype has a higher affinity for epinephrine than norepinephrine?

    <p>β2 receptors</p> Signup and view all the answers

    Which of the following statements about β3 receptors is true?

    <p>They are involved in lipolysis.</p> Signup and view all the answers

    What structural feature of adrenergic drugs is crucial for their potency in activating receptors?

    <p>Number and location of OH substitutions on the benzene ring</p> Signup and view all the answers

    Why are catecholamines ineffective when administered orally?

    <p>They are rapidly metabolized by COMT and MAO in other tissues.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of catecholamines?

    <p>Long duration of action when given parenterally</p> Signup and view all the answers

    Which adrenergic drug is considered a catecholamine?

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

    What is one of the common clinical effects of catecholamines on the CNS?

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

    What is a characteristic of noncatecholamines in comparison to catecholamines?

    <p>They have longer half-lives due to lack of catechol hydroxyl groups.</p> Signup and view all the answers

    Which compound is an analog of epinephrine?

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

    What effect does increased lipid solubility have on noncatecholamines?

    <p>Increased access to the CNS.</p> Signup and view all the answers

    Which compound has an isopropyl substitution on the amine nitrogen?

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

    How does the amine nitrogen substitution of epinephrine affect its potency?

    <p>Increases potency at β receptors.</p> Signup and view all the answers

    Where are A-α1 receptors primarily located?

    <p>On postsynaptic membranes of effector organs</p> Signup and view all the answers

    Which receptor has a greater affinity for phenylephrine compared to clonidine?

    <p>α1 receptors</p> Signup and view all the answers

    What is produced as a result of phospholipase C activation by α1 receptors?

    <p>Inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG)</p> Signup and view all the answers

    Which type of adrenergic agonists act directly on α or β receptors?

    <p>Direct-acting agonists</p> Signup and view all the answers

    What is the primary mechanism of action for indirect-acting agonists?

    <p>Blocking the uptake of norepinephrine</p> Signup and view all the answers

    Which of the following is an example of a mixed-action agonist?

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

    Which of the following statements is true about direct-acting adrenergic agonists?

    <p>They bind directly to adrenergic receptors.</p> Signup and view all the answers

    Which of the following drugs is classified as an indirect-acting agonist?

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

    Study Notes

    Adrenergic Agonists

    • These neurons are found in the CNS and also in the sympathetic nervous system, linking between ganglia and effector organs
    • The adrenergic neurons and receptors (presynaptically on the neuron or postsynaptically on the effector organ)
    • Neurotransmission at adrenergic neurons involves five steps: synthesis, storage, release, receptor binding, and removal of the neurotransmitter from the synaptic gap.

    1-Synthesis of norepinephrine

    • Tyrosine is transported by a Na+-linked carrier into the axoplasm of the adrenergic neuron, where it is hydroxylated to dihydroxyphenylalanine (DOPA) by tyrosine hydroxylase.
    • This is the rate-limiting step in the formation of norepinephrine.
    • DOPA is then decarboxylated by the enzyme DOPA decarboxylase (aromatic l-amino acid decarboxylase) to form dopamine in the cytoplasm of the presynaptic neuron.

    2-Storage of norepinephrine in vesicles

    • Dopamine is then transported into synaptic vesicles by an amine transporter system. This carrier system is blocked by reserpine.

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    Description

    This quiz tests your knowledge on the key processes involved in neurotransmission at adrenergic neurons, including the synthesis and release of norepinephrine. Questions cover the roles of various enzymes and receptors, as well as drug interactions. Challenge your understanding of adrenergic signaling mechanisms!

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