Sympathetic Nervous System Quiz

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Questions and Answers

What is the primary role of α2 receptors in the sympathetic nervous system?

To stimulate the release of norepinephrine

To enhance sympathetic activity

To bind exclusively to epinephrine

To inhibit further release of norepinephrine (correct)

Which of the following statements about β1 and β2 receptors is true?

β1 receptors have approximately equal affinities for epinephrine and norepinephrine. (correct)

β2 receptors respond equally to norepinephrine and epinephrine.

β2 receptors have no role in responding to circulating epinephrine.

β1 receptors have a higher affinity for epinephrine than norepinephrine.

In which type of tissues are β2 receptors predominantly found?

Adrenal medulla

Skeletal muscle vasculature (correct)

Cardiac tissues

Parasympathetic innervated tissues

How do α2 receptors on presynaptic parasympathetic neurons function?

They modulate acetylcholine release. Signup and view all the answers

What mechanism does feedback inhibition serve in the context of sympathetic activity?

To prevent overstimulation of receptors Signup and view all the answers

What is the predominant effect of epinephrine on blood glucose levels?

Stimulating hepatic glycogenolysis Signup and view all the answers

Which route of administration is preferred for epinephrine during anaphylaxis in an outpatient setting?

Intramuscular (anterior thigh) Signup and view all the answers

Which of the following describes a serious side effect of epinephrine?

Cerebral hemorrhage Signup and view all the answers

How is epinephrine primarily metabolized in the body?

By MAO and COMT Signup and view all the answers

In which of the following conditions is epinephrine contraindicated?

Hypertension Signup and view all the answers

What is one of the primary uses of norepinephrine?

Cardiovascular support Signup and view all the answers

Which of the following actions is NOT related to epinephrine's effect on blood glucose levels?

Increasing insulin secretion Signup and view all the answers

What can occur when epinephrine is used in patients on β-blockers?

Hypertensive crisis Signup and view all the answers

What is the primary effect of norepinephrine on blood vessels?

Constricts all blood vessels Signup and view all the answers

Why is norepinephrine not useful in treating bronchospasm?

It does not cause compensatory vasodilation Signup and view all the answers

What occurs as a reflex response when norepinephrine increases blood pressure?

Reflex bradycardia Signup and view all the answers

Which of the following is a reason for the limited therapeutic use of isoproterenol?

Its non-selectivity causes unwanted effects Signup and view all the answers

What is a significant adverse effect of norepinephrine?

Tissue necrosis at the injection site Signup and view all the answers

How is norepinephrine typically administered?

By intravenous infusion Signup and view all the answers

What metabolic pathway is primarily responsible for the breakdown of isoproterenol?

COMT Signup and view all the answers

What effect does isoproterenol have on arterial pressure?

It decreases mean arterial and diastolic blood pressures Signup and view all the answers

What is the primary benefit of using nonselective β-blockers like nadolol and propranolol in patients with portal hypertension?

They reduce the risk of variceal hemorrhage. Signup and view all the answers

Which of the following β-blockers is NOT considered cardioselective?

Labetalol Signup and view all the answers

What unique property does esmolol have compared to other β-blockers?

It has a very short half-life. Signup and view all the answers

What is a common therapeutic use for cardioselective β-blockers?

Chronic heart failure management Signup and view all the answers

What is a significant side effect of labetalol when used for hypertension?

Postural hypotension Signup and view all the answers

Which β-blocker has partial agonist activity, impacting both β1 and β2 receptors?

Acebutolol Signup and view all the answers

What is a consideration when administering cardioselective β-blockers to asthma patients?

Monitor for compromised respiratory activity. Signup and view all the answers

For what condition is intravenous labetalol primarily used?

Hypertensive emergencies Signup and view all the answers

What effect does phenoxybenzamine have on heart rate?

Causes reflex tachycardia due to decreased peripheral resistance Signup and view all the answers

Which condition is phenoxybenzamine primarily used to treat?

Pheochromocytoma Signup and view all the answers

What is a characteristic of phentolamine compared to selective α1-blockers?

Has a rapid onset and short duration of action Signup and view all the answers

What is the primary adverse effect associated with the first dose of prazosin?

Exaggerated orthostatic hypotension Signup and view all the answers

Which of the following is a side effect of both phenoxybenzamine and phentolamine?

Tachycardia and arrhythmias Signup and view all the answers

Why is prazosin suggested to be taken at bedtime?

To reduce the risk of syncope following the first dose Signup and view all the answers

Which of the following adrenergic agonists is primarily used as a bronchodilator?

Salmeterol Signup and view all the answers

What distinguishes selective α1-blockers from nonselective α-blockers in terms of tolerance?

They are less likely to produce tachycardia. Signup and view all the answers

What is the primary receptor action of norepinephrine?

α1 and β1-agonist Signup and view all the answers

What type of receptor does phenoxybenzamine primarily block to achieve its effects?

Both α1 and α2 receptors Signup and view all the answers

Which adrenergic agonist is used as a nasal decongestant?

Phenylephrine Signup and view all the answers

Which adrenergic agonist is NOT primarily classified for uterine relaxation?

Amphetamine Signup and view all the answers

What is the therapeutic use of dobutamine?

Cardiogenic shock Signup and view all the answers

Which of the following is a CNS stimulant?

Methamphetamine Signup and view all the answers

Which agent is used to prolong the duration of local anesthesia?

Epinephrine Signup and view all the answers

Which is an example of a mixed-acting adrenergic agonist?

Ephedrine Signup and view all the answers

What is the main action of phenylephrine?

α1-agonist Signup and view all the answers

Which adrenergic agonist is primarily used to treat glaucoma?

Apraclonidine Signup and view all the answers

Study Notes

Adrenergic Agents

Four classes of drugs (ABCD):
- ACE inhibitors (ARBs)
- Diuretics
- Beta-blockers
- Calcium channel blockers
Adrenergic drugs affect receptors stimulated by norepinephrine or epinephrine
Drugs that activate adrenergic receptors are called sympathomimetics
Drugs that block adrenergic receptors are called sympatholytics
Sympathomimetics are adrenergic agonists

Adrenergic Receptors

Several classes of adrenoceptors can be distinguished pharmacologically.
Two main families of receptors, designated alpha (α) and beta (β), are classified based on their differential responses to the adrenergic agonists, epinephrine, norepinephrine, and isoproterenol.
Both alpha and beta receptor types have specific subtypes.
Alpha-adrenoceptors:
- Respond weakly to isoproterenol
- Respond to epinephrine and norepinephrine
- Divided into subtypes based on affinities for agonists and antagonists.
Beta-adrenoceptors:
- Beta 1 receptors have similar affinities for epinephrine and norepinephrine.
- Beta 2 receptors have a higher affinity for epinephrine than norepinephrine.
Adrenergically innervated organs and tissues have a predominant receptor type.

Adrenergic Receptor Subtypes

a1 receptors: found on postsynaptic effector organs, mediate vascular smooth muscle constriction.
a2 receptors: found on presynaptic nerve endings, mediate feedback inhibition of norepinephrine release.
β1 receptors: found in the heart, increase heart rate and contractility.
β2 receptors: found in smooth muscle of the bronchi, blood vessels, and other organs, mediate relaxation.
β3 receptors: found in adipose tissue, mediate lipolysis.

Synthesis and Release of Norepinephrine (NE)

Synthesis of norepinephrine (NE) begins with tyrosine
NE is stored in vesicles within the presynaptic neuron
Release of NE involves calcium influx causing vesicle fusion (exocytosis)
Removal of NE from synaptic space is via reuptake, or by metabolism (MAO, COMT).

Classification of Sympathomimetics

Based on chemical structure:
- Catecholamines: contain catechol nucleus (e.g., epinephrine, norepinephrine, dopamine, isoproterenol)
- Non-catecholamines: lack catechol nucleus (e.g., tyramine, amphetamine, phenylephrine)

Mechanism of Action of Sympathomimetics

Direct acting agonists: interact directly with adrenergic receptors (e.g., epinephrine, norepinephrine)
Indirect acting agonists: enhance the release of norepinephrine or block its reuptake (e.g., cocaine, amphetamine)

Therapeutic Uses of Sympathomimetics

Based on various therapeutic effects (e.g., shock, bronchodilation, CNS stimulation)

Adverse Effects of Epinephrine

Often due to extension of pharmacological action (e.g. tachycardia, tremors, hypertension)
High concentration can cause acute pulmonary oedema, by shifting blood from systemic to pulmonary circulation
Contraindicated in cardiovascular diseases.

Norepinephrine

Similar to epinephrine: increase blood pressure by vasoconstriction.
Not suitable for oral administration.
Effective treatment for shock

Isoproterenol (Isoprenaline)

Non-selective beta-receptor agonist.
Used in treatment of cardiac arrest.
Not effective orally due to metabolism

Dobutamine

Primarily a beta-1 receptor agonist with minor beta-2 and alpha-1 effects.
Increases heart rate and cardiac output.
Inotropic support in acute heart failure (IV infusion)

Albuterol, Levalbuterol, Metaproterenol, and Terbutaline

Used to treat acute bronchospasm (i.e. asthma ).
β2-adrenergic agonists, effective in relaxation of airways.

Salmeterol, Indacaterol, Olodaterol

Long-acting β2-adrenergic agonists (LABAs).
Management of respiratory disorders, like asthma and COPD, but not recommended as monotherapy for asthma.

Naphazoline, Oxymetazoline, and Tetrahydrozoline

Alpha-1 adrenergic agonists.
Used as nasal decongestants, and ophthalmic drops to improve nasal mucosa or eye redness, respectively.

Mirabegron and Vibegron

Beta-3 adrenergic agonists.
They relax detrusor smooth muscle and increase bladder capacity.
Used in patients with overactive bladders.

Indirect-Acting Adrenergic Agonists

Potentiation of endogenous norepinephrine or epinephrine, acting indirectly to stimulate norepinephrine increase (e.g. amphetamine).

Cocaine

Blocks sodium-chloride-dependent norepinephrine transporter.
Results in increased norepinephrine in the synaptic space, thus increasing sympathetic activity.
A local anesthetic

Ephedrine and Pseudoephedrine

Mixed action adrenergic agonists.
Stimulate both alpha and beta receptors, and enhance release of norepinephrine.

Summary of Important Characteristics of Adrenergic Agonists

Arrhythmias,
Headache,
Hyperactivity,
Insomnia,
Nausea,
Tremors

Adrenergic Antagonists

These drugs block adrenergic receptors.
Classified based on selectivity for alpha (α) or beta (β) receptors.

Phenoxybenzamine

Irreversible, nonselective blocker of alpha-1 and alpha-2 receptors.

Phentolamine

Competitive, nonselective blocker of alpha-1 and alpha-2 receptors.

Prazosin

Selective alpha-1 blocker.
May cause first-dose phenomenon (postural hypotension).

Other Selective alpha-1 Blockers

Terazosin, Doxazosin, Alfuzosin, and Tamsulosin
Used for benign prostatic hyperplasia.

Beta-Adrenergic Blockers

These drugs block beta receptors.
Classified based on selectivity and other properties

Propranolol

Nonselective beta-receptor antagonist.
Useful in hypertension, angina, and arrhythmias.
High lipophilicity, rapidly crosses the blood-brain barrier.

Nadolol and Timolol

Non-selective beta-blockers.
Long duration of action.
Used topically to treat glaucoma.

Acebutolol, Atenolol, Bisoprolol, Esmolol, Metoprolol

Selective Beta-1 antagonists.
Fewer effects compared to non-selective agents

Labetalol

Competitive beta-1, beta-2, and alpha-1 antagonist.
Has additional vasodilatory effects.
Used in hypertensive emergencies and pregnancy.

Carvedilol

Competitive beta-1, beta-2, and alpha-1 antagonist.
Additional antioxidant and vasodilatory properties.
Used in chronic heart failure.

Nebivolol

Selective beta-1 antagonist.
Has nitric oxide-releasing vasodilating activity.

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Description

Test your knowledge on the roles of α2, β1, and β2 receptors in the sympathetic nervous system. This quiz covers the mechanisms of epinephrine and norepinephrine, their effects on blood glucose levels, and administration routes during emergencies. Challenge yourself and deepen your understanding of adrenergic receptors!