Catecholamine Synthesis and Metabolism
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Catecholamine Synthesis and Metabolism

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Questions and Answers

What type of adrenergic agonist is Clonidine classified as?

  • Mixed-action agonist
  • α-2 agonist (correct)
  • β-2 agonist
  • α-1 agonist

    • Which of the following is NOT a characteristic of catecholamines?

  • Ineffective when taken orally
  • Can cross the blood-brain barrier (correct)
  • Short half-life due to rapid elimination
  • Rapidly inactivated by MAO and COMT

    • Adrenaline primarily has which type of action?

  • Selective β-2 action
  • Potent non-selective action on both α and β receptors (correct)
  • Only β-1 action
  • Selective α-1 action

    • Which of the following drugs is classified as a β-1 agonist?

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

    What is the primary characteristic of mixed-action agonists?

    <p>Act both directly on receptors and indirectly via neurotransmitter reuptake</p> Signup and view all the answers

    What distinguishes indirect-acting sympathetics from direct-acting ones?

    <p>They affect neurotransmitter metabolism or reuptake</p> Signup and view all the answers

    Which sympathomimetic drug is known for causing relaxation of bronchial smooth muscle?

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

    Which of the following routes of administration is NOT typically used for catecholamines?

    <p>Oral ingestion</p> Signup and view all the answers

    What is the primary function of catecholamine reuptake via neuronal transporters?

    <p>To regulate catecholamine concentrations in the synaptic space</p> Signup and view all the answers

    Which enzyme is responsible for the metabolism of noradrenaline and serotonin?

    <p>Monoamine oxidase A (MAO A)</p> Signup and view all the answers

    What therapeutic effect do MAO inhibitors provide when used as antidepressants?

    <p>Block the degradation of catecholamines</p> Signup and view all the answers

    Which type of adrenergic receptor is primarily involved in the vasoconstriction effect mediated by noradrenaline?

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

    Which of the following adrenergic receptors is found in adipose tissue?

    <p>β3 receptor</p> Signup and view all the answers

    How does noradrenaline act on presynaptic α2 receptors?

    <p>It ensures autoinhibition of norepinephrine release.</p> Signup and view all the answers

    Which statement best describes the potency of isoprenaline, adrenaline, and noradrenaline at beta adrenergic receptors?

    <p>Isoprenaline is the most potent agonist at beta receptors.</p> Signup and view all the answers

    What is one of the main effects of noradrenaline on adrenergic receptors in the gastrointestinal tract?

    <p>Relaxation of gastrointestinal smooth muscle</p> Signup and view all the answers

    What is primarily affected by adrenaline at low doses?

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

    Which pharmacological effect is associated with high doses of noradrenaline?

    <p>Generalized vasoconstriction</p> Signup and view all the answers

    What is a common adverse drug reaction (ADR) of adrenaline?

    <p>Panic and anxiety</p> Signup and view all the answers

    In which condition is adrenaline NOT typically utilized therapeutically?

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

    What is the primary route of administration for noradrenaline due to its properties?

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

    What is a significant pharmacological effect of adrenaline on blood pressure?

    <p>Increases systolic pressure</p> Signup and view all the answers

    Which of the following consequences can arise from high doses of noradrenaline?

    <p>Necrosis due to vasoconstriction</p> Signup and view all the answers

    What effect does adrenaline have on smooth muscle in pregnant vs. non-pregnant women?

    <p>Contracts in non-pregnant, relaxes in pregnant women</p> Signup and view all the answers

    Which of the following is NOT a pharmacological action of the banned drug?

    <p>Reduced appetite</p> Signup and view all the answers

    What therapeutic application is indicated for the use of adrenaline?

    <p>Cardiac arrest</p> Signup and view all the answers

    Which of the following β2-receptor agonists is used for asthma treatment?

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

    Which of the following is an application of α2 agonists like clonidine?

    <p>To lower blood pressure</p> Signup and view all the answers

    What is a common adverse drug reaction (ADR) associated with the banned drug?

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

    Which of the following nasal decongestants primarily causes rebound vasodilation when used topically?

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

    What is the primary action of Phenylephrine when administered as a nasal decongestant?

    <p>Induces mydriasis and nasal decongestion</p> Signup and view all the answers

    Which α1 agonist is synthetic and specifically direct in its mechanism of action?

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

    Which drug is utilized in the treatment of hypotensive states such as hypovolaemic shock?

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

    Which of the following drugs is associated with the treatment of alcohol withdrawal symptoms?

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

    What is a notable adverse drug reaction (ADR) associated with Phenylephrine?

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

    Which type of receptors does Clonidine primarily act upon in the brain to exert its effects?

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

    Which of the following drugs is known to be a poor bronchodilator and is often combined with other medications?

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

    Study Notes

    Catecholamine Synthesis

    • Catecholamines are neurotransmitters synthesized from the amino acid tyrosine.
    • The synthesis pathway involves several enzymes: tyrosine hydroxylase, dopa decarboxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase (PNMT).
    • The main catecholamines are dopamine, norepinephrine, and epinephrine.

    Reuptake and Inactivation of Catecholamines

    • Neuronal Reuptake: Catecholamines are reabsorbed back into the presynaptic neuron via specialized transporters called catecholamine reuptake transporters (NETs).
    • Extraneuronal Reuptake: Catecholamines can also be taken up by adjacent cells, contributing to the regulation of catecholamine concentrations in the synaptic space.

    Catecholamine Metabolism

    • Monoamine Oxidase (MAO): Enzyme responsible for the breakdown of catecholamines in the presynaptic neuron.
      • MAO inhibitors: Drugs that block MAO activity and lead to increased levels of catecholamines. Used as antidepressants.
      • MAO-A: preferentially metabolizes norepinephrine and serotonin.
      • MAO-B: preferentially metabolizes dopamine.
    • Catechol-O-Methyl-Transferase (COMT): Enzyme responsible for the methylation of catecholamines. This methylation step inactivates catecholamine activity.

    Adrenergic Receptors

    • Adrenergic receptors are G protein-coupled receptors that bind catecholamines to initiate cellular responses.
    • They are divided into α and β subtypes:
      • α1: found in smooth muscles of blood vessels, bronchi, gastrointestinal tract, uterus, and bladder.
      • α2: primarily located on presynaptic nerve terminals.
      • β1: found in the heart, intestinal sphincter.
      • β2: found in smooth muscle of blood vessels, bronchial smooth muscle, and adipose tissue.
      • β3: found in adipose tissue.

    Adrenoceptor Agonist Potencies

    • Alpha agonists: Norepinephrine > epinephrine > isoproterenol
    • Beta agonists: Isoproterenol > epinephrine > norepinephrine

    Effects of Norepinephrine on Adrenergic Receptors

    • α1: Vasoconstriction, relaxation of gastrointestinal smooth muscle, salivary secretion, and hepatic glycogenolysis.
    • α2: Inhibition of norepinephrine release, promotion of platelet aggregation, vascular smooth muscle contraction, and insulin release.
    • β1: Increased cardiac rate and force.
    • β2: Bronchodilation, vasodilation, relaxation of visceral smooth muscle, hepatic glycogenolysis, and muscle tremor.
    • β3: Lipolysis and thermogenesis, bladder detrusor muscle relaxation.

    Sympathomimetic Drugs

    • Drugs that mimic the effects of the sympathetic nervous system by activating adrenergic receptors.
    • They are divided into several categories:
      • Catecholamines: Directly-acting agonists.
      • α agonists: Selective for α1 or α2 receptors.
      • β agonists: Selective for β1 or β2 receptors.
      • Mixed-action agonists: Act on both α and β receptors.

    Catecholamine Drugs

    • Epinephrine (Adrenaline): Non-selective adrenergic agonist with both α and β activity.
      • Pharmacological effects:
        • Cardiocirculatory: Heart rate increase, force of contraction, systolic volume, vasoconstriction, blood pressure increase.
        • Smooth muscle: Bronchodilation, relaxation of uterus (in pregnant women), gastrointestinal relaxation.
        • Metabolism: Hyperglycemia, lipolysis.
        • CNS: Headaches, tremor, restlessness.
      • Therapeutic applications: Cardiac arrest, heart block, shock, superficial hemorrhages, nasal decongestants, to prolong local anesthesia.
    • Norepinephrine (Noradrenaline): Primarily α-agonist, but also has some β activity.
      • Pharmacological effects: Generalized vasoconstriction, blood pressure increase, increased heart rate and force.
      • Therapeutic applications: Controlling local bleeding, severe hypotension, anaphylactic shock, topical nasal decongestant.
    • Dopamine: Stimulates various receptors based on dose:
      • Low doses: D1-receptor stimulation - vasodilation in renal, mesenteric, and coronary vessels.
      • Moderate doses: β1-receptor stimulation - positive inotropic and chronotropic effects on the heart.
      • High doses: α1-receptor stimulation - vasoconstriction and decreased renal blood flow.

    α1 Agonists

    • Nasal Decongestants: Produce vasoconstriction, often found in cold and flu medications.

      • Examples: Naphazoline, Pseudoephedrine, Phenylephrine.

    • Phenylephrine: Selective α1-agonist, long duration of action, resistant to MAO and COMT.

      • Pharmacological effects: Peripheral vasoconstriction, increased blood pressure, mydriasis (pupil dilation), nasal decongestion.
      • Therapeutic applications: Hypotensive shock, sinusitis, rhinitis, mydriatic for eye drops.

    α2 Agonists

    • Clonidine: Centrally-acting α2 agonist that reduces blood pressure and cardiac output.
      • Therapeutic applications: Opioid withdrawal, alcohol withdrawal.
      • Pharmacological actions: Alertness, euphoria, increased physical performance, short-lasting effects.
      • Adverse effects: Dependence, tolerance, anorexia.
    • Other α2 agonists: Used to treat ADHD, narcolepsy, epilepsy, Parkinsonism.

    Clinical Uses of Adrenoceptor Agonists

    • Cardiovascular System:
      • Cardiac arrest: Adrenaline.
      • Cardiogenic shock: Dobutamine (β1 agonist).
      • Anaphylaxis: Adrenaline.
    • Respiratory System:
      • Asthma: Selective β2-receptor agonists (salbutamol, terbutaline, salmeterol, formoterol).
      • Nasal decongestion: Xylometazoline or ephedrine (alpha agonists).
    • Miscellaneous:
      • Adrenaline: Prolongs action of local anesthetics.
      • Salbutamol: Used to delay premature labor.
      • Clonidine: Lowers blood pressure, intraocular pressure, drug withdrawal in addicts, menopausal flushing, migraine prevention.
      • Mirabegron (β3 agonist): Overactive bladder symptoms.

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    Description

    Explore the synthesis, reuptake, and metabolism of catecholamines in this quiz. Understand the role of enzymes like tyrosine hydroxylase and monoamine oxidase in neurotransmitter regulation. Test your knowledge about how catecholamines are produced and inactivated in the nervous system.

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