Adrenergic Agents and Norepinephrine Overview
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Questions and Answers

What is the primary mechanism by which α2 selective agonists reduce sympathetic outflow?

  • Direct vasodilation of blood vessels.
  • Stimulation of presynaptic alpha-2 adrenergic receptors. (correct)
  • Inhibition of presynaptic alpha-2 receptors.
  • Activation of postsynaptic alpha-1 receptors.

    • Which condition is NOT commonly treated with clonidine?

  • Heart failure (correct)
  • Hypertension
  • ADHD
  • Opioid withdrawal

    • Which of the following agents is known for entering the neuron and disrupting vesicular storage mechanisms?

  • Clonidine
  • Norepinephrine
  • Methyldopa
  • Amphetamine (correct)

    • What is a major side effect associated with α2 selective agonists?

    <p>Drowsiness/Sedation (B)</p> Signup and view all the answers

    Which of the following best describes the clinical use of guanabenz?

    <p>Treatment of hypertension (C)</p> Signup and view all the answers

    What is the effect of presynaptic α2 receptor stimulation on norepinephrine release?

    <p>It prevents norepinephrine release. (D)</p> Signup and view all the answers

    Which of the following is an indirect sympathomimetic agent?

    <p>Amphetamine (B)</p> Signup and view all the answers

    What role does NET (norepinephrine transporter) inhibition play in adrenergic drug action?

    <p>Enhances the release of norepinephrine into the synaptic cleft. (B)</p> Signup and view all the answers

    Which drug is a synthetic direct acting β1-selective agonist used primarily for heart failure?

    <p>Dobutamine (B)</p> Signup and view all the answers

    What is a common side effect of sympathomimetic drugs on the cardiovascular system?

    <p>Cardiac arrhythmia (D)</p> Signup and view all the answers

    Which α1 sympathomimetic agent is used in the treatment of orthostatic hypotension?

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

    What effect does Phenoxybenzamine predominantly exert in the body?

    <p>Vasodilation (C)</p> Signup and view all the answers

    Which of the following is a β-blocker that can exhibit intrinsic sympathomimetic activity?

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

    What is a key therapeutic use of Phenylephrine?

    <p>To induce mydriasis (A)</p> Signup and view all the answers

    Which of the following does NOT act as a direct agonist on adrenergic receptors?

    <p>Atenolol (C)</p> Signup and view all the answers

    Which statement regarding Dobutamine's metabolism is correct?

    <p>It is metabolized via oxidative deamination in the liver (C)</p> Signup and view all the answers

    What is the main action of adrenergic neuron blockers?

    <p>Inhibit the synthesis and release of norepinephrine (D)</p> Signup and view all the answers

    Which compound is formed as a false transmitter in the presence of α-methyl dopa?

    <p>Alpha-methyl NE (C)</p> Signup and view all the answers

    What is the role of reserpine in the context of adrenergic agents?

    <p>Inhibits VMAT to deplete catecholamines (C)</p> Signup and view all the answers

    Which of the following best describes the effect of α2 selective agonists?

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

    Which of the following is an action of amphetamine-like agents?

    <p>Increase the release of catecholamines (A)</p> Signup and view all the answers

    What is the primary clinical application of α-methyl dopa?

    <p>Treatment of hypertension (A)</p> Signup and view all the answers

    How do NET inhibitors function within the adrenergic system?

    <p>Inhibit norepinephrine transport back into neurons (C)</p> Signup and view all the answers

    Which compound is primarily released instead of norepinephrine due to false transmitter formation?

    <p>Alpha-methyl norepinephrine (B)</p> Signup and view all the answers

    Flashcards

    Dobutamine

    A synthetic, direct-acting, beta-1 selective agonist used as an inotropic agent for heart failure and shock.

    Beta-1 Adrenoreceptor Agonist

    A drug that stimulates beta-1 receptors, increasing heart rate and contractility.

    Phenylephrine

    A selective alpha-1 agonist used for decongestion, mydriasis, and raising blood pressure.

    Alpha-1 Blocker

    A drug that blocks alpha-1 receptors, leading to vasodilation and lowered blood pressure.

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    Phenoxybenzamine

    A non-selective, irreversible alpha-blocker used for treating severe high blood pressure (malignant hypertension).

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    Sympathomimetic Agent

    A drug that mimics the effects of the sympathetic nervous system.

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    Alpha Blocker (non-selective)

    A drug that blocks both alpha-1 and alpha-2 receptors, leading to various effects.

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    Adrenergic Agonist Side Effects (CVS)

    Side effects on the cardiovascular system, such as hypertension, cardiac arrhythmias, and myocardial infarction (heart attack).

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    Adrenergic Neuron Blockers

    Medications that interfere with norepinephrine (NE) release from sympathetic nerves.

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    False Transmitters

    Substances that mimic norepinephrine and are stored in vesicles but have reduced sympathetic activity due to lower receptor affinity.

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    α-Methyl Dopa

    An example of a false transmitter that is converted into alpha-methyl norepinephrine, reducing sympathetic activity.

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    Reserpine

    A medication that depletes catecholamines by inhibiting VMAT (vesicular monoamine transporter).

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    VMAT

    Vesicular monoamine transporter, the mechanism for storing catecholamines in adrenergic vesicles.

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    Catecholamines

    Neurotransmitters like norepinephrine, and in this context, affected by reserpine.

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    Inhibition of Release

    Drugs that prevent the release of norepinephrine, affecting sympathetic function.

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    Reduced Sympathetic Activity

    A decrease in the effects of the sympathetic nervous system by one of the above-mentioned processes.

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    Sympatholytic Agents

    Drugs that reduce sympathetic activity, lowering blood pressure and heart rate. This is achieved by reducing norepinephrine release or by stimulating alpha-2 receptors.

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    α2-Selective Agonists: Mechanism

    These drugs primarily activate presynaptic α2 receptors in the central nervous system, reducing norepinephrine release, leading to decreased sympathetic tone and lower blood pressure.

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    Clonidine

    A commonly used α2-selective agonist for treating hypertension, also employed for opioid withdrawal, ADHD, and hot flashes.

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    Methyldopa

    An α2-selective agonist specifically used for hypertension during pregnancy.

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    Guanethidine

    A drug that blocks norepinephrine release from sympathetic nerve terminals, effectively reducing sympathetic activity.

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    Indirect Sympathomimetics: Mechanism

    These drugs enter nerve cells and interfere with the storage of neurotransmitters (like dopamine and norepinephrine) in vesicles, causing an increase in their release and a boost in nerve signaling.

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    Amphetamine-like Agents

    A type of indirect sympathomimetic that enters neurons and disrupts vesicular storage mechanisms, leading to increased release of neurotransmitters, particularly dopamine and norepinephrine.

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    Study Notes

    Adrenergic Agents: Agonists and Antagonists

    • Adrenergic agents are drugs that mimic or block the effects of the sympathetic nervous system. They work by affecting receptors in the body.

    Synthesis of Norepinephrine

    • The rate-limiting step in norepinephrine synthesis is the hydroxylation of tyrosine.

    Norepinephrine Uptake

    • Norepinephrine is actively transported into storage vesicles where it is protected from degradation.
    • Reserpine inhibits this transport.

    Norepinephrine Release

    • Calcium influx triggers the release of norepinephrine from vesicles into the synaptic cleft.
    • Guanethidine and bretylium block this release.

    Norepinephrine Metabolism

    • Norepinephrine is metabolized by enzymes like COMT (catechol-O-methyltransferase) and MAO (monoamine oxidase).

    Removal of Norepinephrine

    • Norepinephrine is rapidly taken back up into the presynaptic neuron.
    • Inhibitors like cocaine and imipramine block this reuptake.

    Binding to Receptors

    • Norepinephrine binds to postsynaptic receptors, activating them.

    Adrenergic Neuron Blockers

    • Form false transmitters (e.g., α-methyl dopa).
    • Deplete storage sites (e.g., reserpine).
    • Inhibit release and enhance uptake (e.g., guanethidine).
    • Stimulate presynaptic α2 receptors (e.g., clonidine, α-methyl dopa).

    α2 Selective Agonists

    • Clonidine, methyldopa, guanabenz, and guanfacine are used for hypertension, opioid withdrawal, ADHD, and hot flashes.
    • Major side effects are drowsiness and sedation.
    • The indication/use is primarily hypertension.

    Effects in Humans: Epinephrine, Norepinephrine, & Isoprenaline

    • IV infusions of epinephrine, norepinephrine, and isoprenaline show different effects on blood pressure, peripheral resistance, and heart rate.

    Indirect Sympathomimetics -1

    • Amphetamine-like agents enter neurons.
    • Interact with VMAT2.
    • Promote neurotransmitter release increasing cytoplasmic neurotransmitter.
    • Used for ADHD (e.g. amphetamine, methamphetamine, methylphenidate, modafinil).

    Indirect Sympathomimetics -2

    • Cocaine, Duloxetine, Atomexetine, Reboxetine inhibit neurotransmitter reuptake, increasing neurotransmitter concentrations.
    • Duloxetine and Atomexetine are antidepressants. Reboxetine is a norepinephrine reuptake inhibitor.

    Clinical Use of Amphetamine-Like Drugs

    • ADHD (Methylphenidate, Dexamfetamine)
    • Narcolepsy (Amphetamine-like drugs to stimulate CNS, Dexamfetamine and Modafinil)
    • Suppress appetite (not currently used)

    Amphetamine

    • Non-selective adrenergic agonist.
    • Acts mainly indirectly by enhancing norepinephrine (NE) and dopamine (DA) release
    • Lipid-soluble, absorbed from intestines, stimulating the CNS (e.g., restlessness, insomnia)
    • Half-life (t1/2) is 45-60 minutes.
    • Metabolized in the liver.

    Amphetamines - Side Effects

    • Chronic use causes tolerance, tachyphylaxis, dependence, addiction, paranoia, psychosis, and hypertension.

    Beta Receptors on Body Organs

    • Eyes: Beta receptors in the ciliary epithelium produce aqueous humor. Blocking receptors decreases humor production.
    • CVS: Beta 1 receptors in the heart increase heart rate with stimulation.
    • Pulmonary: Beta 2 receptors cause bronchodilation in bronchial smooth muscles.
    • Kidney: Promotes renin release, contributes to blood pressure regulation.

    β1 and β2 – Adrenoceptor Agonists

    • Stimulation leads to increased cAMP levels, cellular effects, increased calcium release in the heart, and relaxation in smooth muscles.
    • Effects include increasing heart contractility and rate, relaxing smooth muscles.

    Adrenoceptors (beta)

    • Beta 1 receptors, the site & stimulation effects are on heart
    • Beta 2 receptors, bronchodilation effects are in the bronchial smooth muscle
    • Beta 3 receptors are in adipose tissue & regulates metabolism

    Clinical Effects of β-receptor Stimulation

    • β1 stimulation increases heart rate, myocardial contractility, lipolysis, and renin release.
    • β2 stimulation relaxes bronchi, smooth muscle of arterioles, skeletal muscles, and uterus.
    • β3 stimulation increases lipolysis and heat production.

    β1 Selective Agonists & Antagonists

    • Dobutamine is a β1 selective agonist.
    • Atenolol, esmolol, metoprolol, and others are β1 selective antagonists used for hypertension, angina, and arrhythmias.

    Beta 1 Adrenoreceptor Agonist: Dobutamine

    • Synthetic, direct-acting β1-selective agonist.
    • Short half-life (10-15 min)
    • Metabolized in the liver
    • Increases cardiac output (CO) with minimal effect on heart rate (HR).
    • Less arrhythmogenic than dopamine.
    • Used in heart failure and septic/cardiogenic shock.

    Sympathomimetic Catecholamines

    • Endogenous catecholamines (norepinephrine, epinephrine, dopamine).
    • Synthetic catecholamines (isoprenaline). -a1 sympathomimetic agents (midodrine, phenylephrine).
    • Oxymetazoline.

    Adrenoreceptor Agonists: Side Effects

    • Cardiovascular side effects of sympathomimetic drugs include hypertension, cardiac arrhythmias, myocardial infarction, and angina exacerbation.
    • Eyes: Increased Intraocular Pressure (IOP) leading to glaucoma.

    Adrenoreceptor Antagonists

    • α-blockers (non-selective and selective)
    • β-blockers (non-selective, selective, and with intrinsic sympathomimetic activity (ISA)).

    Alpha Blockers (non-selective)

    • Phenoxybenzamine (non-competitive, irreversible) and phentolamine (competitive, reversible) block α-adrenergic receptors, primarily affecting α1 receptors.
    • Uses include malignant hypertension, pheochromocytoma, and clonidine withdrawal.
    • Decreases heart workload, reducing risk of myocardial infarction.

    Alpha 1 Selective Blockers

    • Alpha 1 blockers (prazosin, terazosin, doxazosin, tamsulosin) block alpha-1 receptors.
    • Uses include hypertension, benign prostatic hyperplasia (BPH), and Raynaud's phenomenon
    • Side effects include nasal congestion and hypotension.

    Beta Blockers (β1 selective)

    • Atenolol, betaxolol, esmolol, metoprolol, bisoprolol, and nebivolol block β1-receptors.

    Beta Blockers (non-selective)

    • Propranolol, timolol, nadolol, and pindolol block both beta 1 and 2 receptors.
    • Contraindicated in asthma patients due to potential bronchospasm.

    Beta Blockers - Uses

    • Hypertension, angina pectoris, cardiac arrhythmias, myocardial infarction, glaucoma, migraine, thyrotoxicosis, and essential tremors.

    Beta Blockers with ISA

    • Acebutolol, PIndolol
    • Lower blood pressure while maintaining heart rate.

    Alpha and Beta Antagonists

    • Labetalol and carvedilol block both alpha and beta receptors and are used to treat hypertension, particularly during pregnancy and in severe hypertension.

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    Adrenergic Agents, Agonists & Antagonists PDF

    Description

    This quiz focuses on adrenergic agents, specifically their agonists and antagonists, and the synthesis, release, metabolism, and removal of norepinephrine. Test your knowledge on key concepts such as receptor binding and transport mechanisms involved in the sympathetic nervous system.

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