sympathomimetics

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Questions and Answers

What is the mechanism of action of adrenaline primarily focused on?

  • Local vasodilation
  • Selective vasoconstriction of coronary vessels
  • Inhibition of MAO and COMT
  • Binding to alpha and beta adrenergic receptors (correct)

How does adrenaline affect intraocular pressure (IOP)?

  • Causes mydriasis, leading to increased IOP
  • Increases IOP by stimulating beta receptors
  • Decreases IOP by facilitating trabecular outflow (correct)
  • Has no effect on IOP

What happens to the bladder wall when adrenaline acts on beta receptors?

  • It has no effect on the bladder wall
  • It constricts the bladder wall
  • It relaxes the bladder wall (correct)
  • It only affects the bladder sphincter

Which of the following is NOT a systemic effect of adrenaline?

<p>Skeletal muscle contraction (C)</p> Signup and view all the answers

What physiological effect does adrenaline exhibit during anaphylactic shock?

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

What effect does adrenaline have on carbohydrate metabolism?

<p>Stimulates glycogenolysis, leading to hyperglycemia (A)</p> Signup and view all the answers

Which adrenergic receptor is responsible for vasoconstriction of ciliary vessels, affecting aqueous humor dynamics?

<p>Alpha-1 (B)</p> Signup and view all the answers

In late pregnancy, what is the effect of adrenaline on the uterus?

<p>Relaxation of the uterine wall (D)</p> Signup and view all the answers

Which statement about the metabolism of adrenaline is correct?

<p>It undergoes metabolism by MAO and COMT (C)</p> Signup and view all the answers

What characterizes the action of sympathomimetics?

<p>They stimulate adrenoceptors and mimic sympathetic nerve actions. (B)</p> Signup and view all the answers

Which receptor subtype is primarily responsible for vasoconstriction and mydriasis?

<p>Alpha-1 adrenoreceptors (B)</p> Signup and view all the answers

What effect do alpha-2 adrenoreceptors generally have on the sympathetic nervous system?

<p>Decrease the release of noradrenaline. (C)</p> Signup and view all the answers

Which of the following is a characteristic action of beta-2 adrenoreceptors?

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

Which drug is an agonist for beta-1 adrenoreceptors?

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

What is a key reason sympathomimetic drugs must be stored in dark containers?

<p>They degrade in the presence of light. (D)</p> Signup and view all the answers

Which of the following effects is associated with activation of beta-3 adrenoreceptors?

<p>Lipolysis in fat cells (B)</p> Signup and view all the answers

Which statement is true regarding adrenaline (epinephrine)?

<p>It is primarily produced in the adrenal medulla. (A)</p> Signup and view all the answers

What type of receptor is primarily targeted by antihypertensive medications such as clonidine?

<p>Alpha-2 adrenoreceptors (D)</p> Signup and view all the answers

Which of the following actions is NOT associated with beta-1 adrenoreceptors?

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

What is a primary systemic use of adrenaline?

<p>Cardiac resuscitation in cardiac arrest (B)</p> Signup and view all the answers

Which adverse effect is most specifically associated with β1-adrenergic receptor stimulation?

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

In which condition is noradrenaline contraindicated due to the risk of severe complications?

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

What is a pharmacological effect of noradrenaline on blood vessels?

<p>Generalized vasoconstriction, except in coronary vessels (A)</p> Signup and view all the answers

What symptom is most likely if extravasation occurs during noradrenaline infusion?

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

Which medication is primarily used to counteract adverse β1 effects?

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

What effect does Isoprenaline primarily exert?

<p>Non-selective β agonist (A)</p> Signup and view all the answers

Which of the following is a consequence of severe extravasation of noradrenaline?

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

What is a significant use of dopamine in clinical settings?

<p>Support during acute heart failure (B)</p> Signup and view all the answers

What is one of the primary adverse effects of isoprenaline due to its β agonistic effects?

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

Which receptor's stimulation primarily leads to peripheral vasodilation effects?

<p>D1 (D)</p> Signup and view all the answers

What is the primary effect of dopamine when administered at a moderate dose?

<p>Positive inotropic effect (C)</p> Signup and view all the answers

Which of the following is an adverse effect associated with the use of dopamine?

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

Which of the following is NOT a clinical use of fenoldopam?

<p>Direct stimulation of β1 receptors (A)</p> Signup and view all the answers

Which mechanism of action is associated with ephedrine?

<p>Indirect action with some direct action on α and β receptors (D)</p> Signup and view all the answers

What consequence can arise from chronic use of nasal decongestants?

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

Which is a primary effect of α1 receptor stimulation when using vasopressors?

<p>Increased total peripheral resistance (D)</p> Signup and view all the answers

What is the primary clinical indication for administering dobutamine?

<p>Positive inotropic support in cardiogenic shock (B)</p> Signup and view all the answers

Which effect is directly associated with stimulation of the D2 receptor?

<p>Decrease dopamine release (B)</p> Signup and view all the answers

Which of the following conditions is NOT treated by α1 agonists?

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

Flashcards

Catecholamine Synthesis

The process of creating catecholamines, like adrenaline and noradrenaline, within the body

Adrenergic Receptors

Specific receptors that bind to adrenaline-like substances and trigger various actions in the body

Alpha 1 Receptors

Postsynaptic receptors that cause vasoconstriction, pupil dilation, and other sympathetic responses.

Alpha 2 Receptors

Receptors in the nervous system that reduce norepinephrine release and regulate other functions.

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Beta 1 Receptors

Receptors that increase heart rate and force of contraction, as well as renin release.

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Beta 2 Receptors

Receptors that cause bronchodilation, insulin release, and other metabolic effects.

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Sympathomimetics

Substances that mimic the actions of the sympathetic nervous system (fight or flight).

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Adrenaline (Epinephrine)

Catecholamine that triggers various physiological responses related to stress or emergency situations.

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Catecholamine Storage

Stored in specialized vesicles inside cells in the body.

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Neuronal Uptake

Absorption of neurotransmitters back into nerve endings.

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Adrenaline's Action on Blood Vessels

Adrenaline causes vasoconstriction in some blood vessels (like skin and mucous membranes) and vasodilation in others (like skeletal muscles and coronary arteries).

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Adrenaline's Effect on the Heart

Adrenaline increases heart rate, strength of contraction, and other properties of the heart.

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Adrenaline's Bronchodilator Effect

Adrenaline relaxes the bronchial muscles, widening the airways, which is crucial for breathing.

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Adrenaline and Blood Pressure

Adrenaline's effects on blood vessels generally leads to increased blood pressure due to vasoconstriction, but can also have vasodilation effects that somewhat counter this.

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Adrenaline and the Eyes

Adrenaline causes vasoconstriction in the eye, reducing aqueous humor production, which helps to lower intraocular pressure (IOP).

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Adrenaline and Blood Sugar

Adrenaline increases blood sugar levels by triggering the breakdown of glycogen (stored sugar) into glucose.

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Adrenaline and Metabolism of Lipids

Adrenaline increases the breakdown of fats (lipolysis), releasing free fatty acids into the bloodstream.

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Adrenaline and Gastrointestinal Tract

Adrenaline constricts sphincters and relaxes the intestinal wall which can impact digestion and other digestive processes.

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Adrenaline in Anaphylaxis

Adrenaline is crucial in anaphylactic shock, acting as an antagonist to histamine, counteracting its symptoms with bronchodilation and vasoconstriction.

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Adrenaline in Local Anesthetics

Adrenaline with local anesthetics reduces the absorption of anesthetic, which results in longer durations and lower systemic side effects.

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Dopamine's Peripheral Effect

Dopamine, when acting at the D1 receptor, causes vasodilation, leading to increased renal blood flow.

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Dopamine's Moderate Dose Effect

At moderate doses, both D1 and β1 receptors are stimulated, resulting in a positive inotropic effect (increased heart muscle contraction).

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Dopamine's Large Dose Effect

High doses of dopamine activate α1 receptors, causing vasoconstriction which increases peripheral resistance and blood pressure.

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Dopamine's Central Mechanism

Dopamine itself cannot cross the blood-brain barrier, but its precursor L-dopa can, allowing it to be converted into dopamine in the brain.

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Dobutamine's Effect

Selectively stimulates β1 receptors, causing a positive inotropic and dromotropic effect (increased heart rate), with minimal impact on peripheral resistance and heart rate.

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Fenoldopam's Mechanism

A direct-acting selective D1 agonist, causing vasodilation, lowering total peripheral resistance and blood pressure.

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Alpha 1 Agonists and Vasoconstriction

α1 receptors, when stimulated, cause vasoconstriction, increasing total peripheral resistance and blood pressure.

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Common Alpha 1 Agonists

Noradrenaline, Ephedrine, Phenylephrine, and Midodrine are examples of α1 agonists that increase blood pressure.

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Nasal Decongestants: Local Application

Topical application of α1 agonists causes vasoconstriction in the nasal mucosa, relieving congestion.

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Nasal Decongestants: Long-Term Use

Chronic nasal decongestant use can cause atrophic rhinitis due to persistent vasoconstriction and rebound congestion.

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Noradrenaline (Norepinephrine)

A natural sympathomimetic catecholamine used in cases of acute hypotension and to constrict blood vessels. It is primarily an α-adrenergic receptor agonist and exhibits limited β2-adrenergic receptor activity. It is not orally administered, does not cross the BBB, and is used by IV infusion.

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Noradrenaline's Use in Hypotension

Noradrenaline is used to treat acute hypotension, particularly during spinal anesthesia or post-operative shock, by increasing blood pressure and improving circulation.

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Noradrenaline Administration Precautions

Noradrenaline must be administered intravenously with strict care, as extravasation can lead to gangrene. Blood pressure and ECG monitoring is crucial during infusion, and gradual withdrawal is recommended to prevent sudden hypotension.

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Isoprenaline's Main Adverse Effects

Isoprenaline's main adverse effects are tachycardia, angina, and arrhythmia, due to its potent stimulation of the heart.

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Dopamine

A natural sympathomimetic catecholamine with a range of effects that depend on its concentration. It acts as a precursor to norepinephrine and is used in various medical conditions.

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Dopamine's Actions in the Body

Dopamine has varying effects on blood vessels, the heart, and kidneys depending on dosage. At low doses, it primarily dilates renal blood vessels. At intermediate doses, it stimulates β1 receptors, increasing heart rate and contractility, while at higher doses, it causes vasoconstriction and increases blood pressure.

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Dopamine's Use in Shock

Dopamine is often used in the treatment of shock, particularly cardiogenic and septic shock, to increase blood pressure and improve myocardial function.

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Dopamine's Administration Precautions

Dopamine must be administered intravenously with careful monitoring due to its potential for adverse effects such as arrhythmias, nausea, and tissue damage. Continuous monitoring is required, and careful dosage adjustment is necessary.

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Study Notes

Credit Hours

  • Tanta Medical Program
  • Credit hours for the program

Sympathomimetics

  • Topic: Sympathomimetics
  • Presenter: Dr. Ola Mousa Salem
  • Interactive session
  • Type of session: lesson
  • Objectives (ILOs):
    • Recognize catecholamine synthesis, storage, and release.
    • Identify different types of adrenergic receptors and their function.
    • Recognize sympathomimetics (action, uses, side effects, and contraindications).

Autonomic Nervous System

  • Diagram showing the autonomic nervous system, its components (nervous system, central, sensory, somatic, motor, ANS), and its divisions (sympathetic and parasympathetic).

Adrenergic Neuronal Transmission

  • Diagram illustrating adrenergic neuronal transmission, including catecholamine synthesis, storage, and release (dopamine, norepinephrine).
  • Steps in the process are shown:
    • Tyrosine to Dopa
    • Dopa to Dopamine
    • Dopamine to Norepinephrine
    • Norepinephrine storage and release
    • Norepinephrine metabolism
    • Reuptake
  • Key players in the process include:
    • Tyrosine hydroxylase
    • Dopa decarboxylase
    • Dopamine β-hydroxylase
    • Enzymes (MAO, COMT)

Fate of Neurotransmitters

  • Neuronal uptake is a major part of the fate of neurotransmitters.
  • Granular uptake (vesicular uptake) is another important process.
  • Metabolism by specific enzymes (MAO-COMT).
  • Stimulation of presynaptic alpha adrenoreceptors.

Alpha & Beta Adrenoreceptors

  • Table explaining the coupling mechanisms of alpha and beta adrenoreceptors.
    • Alpha 1 (Gq-coupled) → Phospholipase C → IP3, DAG, Ca²⁺
    • Alpha 2 (Gq-coupled) → ↓ Adenylyl cyclase → ↓ cAMP
    • Beta (Gs-coupled) → ↑ Adenylyl cyclase → ↑ cAMP

Alpha Adrenoreceptors (α1) (Post)

  • Key effects of alpha1 adrenoreceptors:
    • Contraction of erector pilae muscle
    • Mydriasis (pupil dilation)
    • Vasoconstriction
    • Viscid salivation
    • Gastrointestinal tract (GIT) & urinary bladder (UB) sphincter spasm
    • Uterine contraction (during pregnancy), relaxation (outside pregnancy)
    • Facilitation of neurotransmission
    • Agonist: phenylephrine. Antagonist: prazosin.

Alpha Adrenoreceptors (α2) (Pre & Post)

  • Key effects of alpha2 adrenoreceptors:
    • ↓ Sympathetic outflow from CNS
    • Presynaptic (autoreceptors): influence norepinephrine release
    • Reduce release of noradrenaline
    • Relaxation of intestinal wall (due to ACh release in enteric ganglia)
    • Reduced release of renin and insulin
    • Reduced lipolysis in fat cells
    • Increased platelet aggregation
    • Agonist: clonidine. Antagonist: yohimbine

Beta Adrenoreceptors (β1)

  • Key effects of beta1 adrenoreceptors:
    • CNS stimulation
    • Cardiac stimulation
    • ↑ Release of renin
    • Lipolysis and free fatty acid release
    • Agonist: dobutamine Antagonist: atenolol

Beta Adrenoreceptors (β2)

  • Key effects of beta2 adrenoreceptors:
    • Generalized vasodilation (VD)
    • Bronchodilation
    • Stimulate insulin release
    • Glycogenolysis in liver and skeletal muscles
    • Relaxation of GIT, bladder, and uterus
    • Skeletal muscle tremors
    • Agonist: salbutamol. Antagonist: butoxamine

Sympathomimetics

  • Drugs that stimulate adrenergic receptors. 
  • Produce effects similar to sympathetic nerve stimulation.

Adrenaline (Epinephrine)

  • Sympathomimetic catecholamine found in adrenal medulla and CNS.
  • Stored in dark brown ampoules due to chemical instability in alkaline environments.
  • Administration routes (not orally, I.V., I.M., S.C., inhalation, eye drops, intracardiac).
  • Distribution: Does not pass the blood-brain barrier (BBB).
  • Fate: Nerve and tissue reuptake, metabolism by MAO and COMT; excreted unchanged.
  • Mechanism of action: Stimulates all adrenergic receptors (alpha 1&2, beta 1&2&3).
  • Pharmacological effects (local and systemic).

Local Effects of Adrenaline

  • Skin: Subcutaneous (a1) receptor → vasoconstriction
  • Mucous membranes (nose): vasoconstriction via a1, decongestion, homeostasis
  • Eye: Vasoconstriction of conjunctival blood vessels; no mydriasis (pupil dilation) with adrenaline. (Explain why?)
  • Aqueous humor dynamics: a1 → reduced aqueous formation, B2 → facilitation of trabecular outflow.
  • Bronchi: Decongestion of bronchial mucosa (a1), bronchodilation (β2)

Systemic Effects of Adrenaline

  • CNS: Mild stimulation leads to anxiety.
  • Eye: Systemically (a1) → stimulation of dilator papillae muscle → active mydriasis.
  • Cardiovascular system: affect heart and blood vessels
  • Respiratory system: Bronchodilation, bronchoconstriction
  • Gastrointestinal tract: sphincter constriction, intestinal wall relaxation
  • Urinary bladder: Bladder sphincter constriction, bladder wall relaxation.
  • Uterus: Contraction or relaxation based on pregnancy stage.

Adrenaline (Epinephrine) - Metabolism

  • Carbohydrates: Glycogenolysis → hyperglycemia (β2).
  • Lipids: Lipolysis → increased plasma free fatty acid (β2 + β3).
  • Skeletal muscles...
  • Anti-allergic effect.
  • Transient hyperkalemia

Adrenaline (Epinephrine) - Uses

  • Local uses: Open angle glaucoma, haemostatic nasal pack in epistaxis.
  • Systemic uses: Anaphylactic shock, acute bronchial asthma, acute insulin hypoglycemia, cardiac resuscitation, uterine contractions during labor.

Adrenaline (Epinephrine) - Adverse Effects

  • CNS: Anxiety, headache
  • Alpha effects: Gangrene, hypertension, cerebral hemorrhage.
  • Beta effects: Tachycardia, palpitation, angina, arrhythmia.
  • Beta 2: Skeletal muscle tremors

Adrenaline (Epinephrine) - Contraindications and Drug Interactions

  • Gangrene in fingers and toes
  • Hypertension
  • Hemorrhagic shock, leading to renal failure and death
  • Drug interactions: With digitalis, pulmonary embolism, general anaesthesia.

Noradrenaline (Norepinephrine)

  • Natural sympathomimetic catecholamine
  • Not orally, does not pass BBB, fate like adrenaline. IV infusion.
  • Mechanism of action: Very effective α-adrenergic receptor agonist, limited β2-adrenergic receptor activity.
  • Pharmacological Effects
    • Cardiovascular system: Generalized vasoconstriction (except coronary), increased blood pressure, bradycardia, increased stroke volume but decreased cardiac output, increased excitability and automaticity (leading to arrhythmia).

Noradrenaline (Norepinephrine) - Uses

  • Acute hypotension: during spinal anesthesia or post-operative shock.
  • Local anesthetics

Noradrenaline (Norepinephrine) - Adverse Effects

  • Necrosis and gangrene if extravasation (leakage outside a vein).
  • Hypertension → cerebral hemorrhage.
  • Reflex bradycardia
  • Headache and anxiety.

Isoprenaline (Isoproterenol)

  • Synthetic direct-acting sympathomimetic catecholamine.
  • Nonselective β agonist
  • Use: Acute heart block, acute bronchial asthma
  • Adverse effects: Tachycardia, angina, arrhythmia

Dopamine

  • Natural sympathomimetic catecholamine
  • Mechanism of action: Stimulates dopaminergic receptors, α and β receptors. DOP receptors: D1, D2, D3
  • Peripheral effects: Small dose: D1 → ↑ RBF, moderate dose: D1+β1→ ↑ inotropy, large dose: α1 → ↑ TPR
  • Central effects: Limbic system (euphoria, psychosis), Basal ganglia (antiparkinsonism), Hypothalamus (pyrexia,↓ appetite,↓ prolactin secretion), CTZ (Nausea & vomiting)
  • Uses: Shock, resistant heart failure
  • Side effects: Tachycardia, arrhythmias, nausea, vomiting

Fenoldopam

  • Direct selective D1 agonist → vasodilation
  • ↓ total peripheral resistance and blood pressure

Alpha-Stimulants

  • Stimulation of a1-receptors → vasoconstriction → ↑ total peripheral resistance (TPR) → ↑ blood pressure (BP).
  • Uses: Treat hypotension
  • Examples: Noradrenaline, Ephedrine, Phenylephrine, Midodrine

Nasal Decongestants

  • Topical α1 agonists → vasoconstriction of nasal mucosa.
  • Longer duration of action (e.g., 12 hours) than ephedrine.
  • Uses: Allergic rhinitis, common cold
  • Side effects: Orally → hypertension (cautious use in hypertensives and MAO inhibitors), chronic use → atrophic rhinitis, repeated topical use → rebound congestion.
  • Preparations: Oral (pseudoephedrine, phenylephrine); topical (xylometazoline, naphazoline, tetrahydrozoline, oxymetazoline)

Ephedrine

  • Mechanism of action: Primarily indirect; some direct action on α and β receptors.
  • Effects similar to adrenaline but weaker, slower onset, longer duration, and tachyphylaxis.

Additional notes (from the last page questions)

  • A patient receiving intravenous penicillin and diagnosed with anaphylactic shock should be treated with epinephrine, phenylephrine, or norepinephrine.
  • Prazosin (alpha-blocker) before norepinephrine can cause sustained hypertension.
  • Reflex bradycardia induced by norepinephrine can be blocked by dopamine, isoprenaline, atropine, or ephedrine.

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