Pharmacology of Sympathomimetics

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Questions and Answers

What is a potential consequence of combining tyramine with monoamine oxidase inhibitors like Phenelzine?

Increased serotonin production

Hypertensive crisis (correct)

Decreased anxiety levels

Reduced norepinephrine levels

Which drug class is known for blocking the neuronal uptake of norepinephrine?

Monoamine oxidase inhibitors

Tricyclic antidepressants (correct)

Beta blockers

Selective serotonin reuptake inhibitors

Which of the following is NOT classified as an indirect acting sympathomimetic drug?

Duloxetine (correct)

Amphetamines

Pseudoephedrine

Methylphenidate

Which of the following mixed acting sympathomimetic drugs can also release norepinephrine?

Ephedrine Signup and view all the answers

Which of the following statements is true regarding sympathomimetic drugs?

Mixed acting sympathomimetic drugs can both release and block the reuptake of norepinephrine. Signup and view all the answers

What neurotransmitter is released from all preganglionic nerves in the sympathetic nervous system?

Acetylcholine Signup and view all the answers

Which statement correctly describes the postganglionic nerves in the parasympathetic nervous system?

They release acetylcholine. Signup and view all the answers

Where do the ganglia of the sympathetic nervous system usually reside?

Near the spinal cord Signup and view all the answers

Which of the following contains the sympathetic cholinergic nerves?

Sweat glands Signup and view all the answers

What is the primary function of the parasympathetic nervous system?

Conserve energy Signup and view all the answers

Which drug is primarily used for treating bronchoconstriction?

Albuterol Signup and view all the answers

What is the main therapeutic use of Ephedrine?

Hypotension Signup and view all the answers

What type of cells in the adrenal gland release catecholamines?

Chromaffin cells Signup and view all the answers

Which combination is used for appetite suppression in obesity?

Phentermine + topiramate Signup and view all the answers

What neurotransmitter is predominantly released from postganglionic nerves in the sympathetic nervous system?

Norepinephrine Signup and view all the answers

What is a common adverse effect associated with adrenergic drugs affecting the cardiovascular system?

Tachycardia Signup and view all the answers

Which region does the parasympathetic nervous system NOT originate from?

Thoracic region Signup and view all the answers

Which drug is primarily used in emergency situations for severe allergic reactions?

Epinephrine Signup and view all the answers

Which adrenergic agent is indicated for treating overactive bladder?

Mirabegron Signup and view all the answers

What is a caution for using adrenergic drugs in patients with diabetes mellitus?

Increased blood pressure Signup and view all the answers

Which adrenergic agent is recommended for treating nasal congestion?

Oxymetazoline Signup and view all the answers

Which neurotransmitter is primarily associated with activating cholinergic receptors?

Acetylcholine Signup and view all the answers

What type of receptors do norepinephrine and epinephrine activate?

Adrenergic receptors Signup and view all the answers

Which adrenergic receptor subtype is specifically activated by phenylephrine?

α1 Signup and view all the answers

Which of the following is a known drug that acts as a beta receptor antagonist?

Metoprolol Signup and view all the answers

What distinguishes nicotinic receptors from muscarinic receptors?

Nicotinic receptors are activated by nicotine. Signup and view all the answers

Which drug acts on α2 adrenergic receptors?

Clonidine Signup and view all the answers

Which receptor subtype does atropine antagonize?

Muscarinic receptors Signup and view all the answers

Epinephrine primarily activates which class of receptors?

Alpha and beta receptors Signup and view all the answers

Which of the following is NOT a subtype of beta adrenergic receptors?

α1 Signup and view all the answers

What is the mechanism of action for mecamylamine?

Nicotinic antagonist at neuronal receptors Signup and view all the answers

What does the 'SLUD' syndrome stand for in autonomic effects?

Salivation, Lacrimation, Urination, Defecation Signup and view all the answers

What is the primary effect of cholinesterase inhibitors on nicotinic receptors at the neuromuscular junction?

Facilitation of voluntary contraction Signup and view all the answers

Which condition can be treated with cholinesterase inhibitors?

Myasthenia Gravis Signup and view all the answers

What symptom is indicative of a myasthenic crisis?

Sudden worsening of myasthenic symptoms Signup and view all the answers

What is the effect of succinylcholine on Nm receptors?

It causes prolonged activation leading to paralysis Signup and view all the answers

What is the diagnostic test used to identify Myasthenia Gravis?

Edrophonium (Tensilon) test Signup and view all the answers

Which condition requires increasing cholinesterase inhibition during a myasthenic crisis?

Myasthenia Gravis Signup and view all the answers

How do cholinesterase inhibitors affect neuromuscular blocking drugs?

They increase the concentration of acetylcholine, reversing blockade Signup and view all the answers

What are the classic symptoms of overdose toxicity associated with sympathomimetic drugs?

Hot, red, dry, and mad Signup and view all the answers

Which of the following is an antidote for overdose toxicity from sympathomimetic drugs?

Physostigmine Signup and view all the answers

What type of sympathomimetic drug directly binds to adrenergic receptors?

Direct Acting Sympathomimetic Drugs Signup and view all the answers

Which statement accurately describes the 'low dose effect' of epinephrine?

It decreases blood pressure at low doses. Signup and view all the answers

Which of the following is an example of a β2-selective agonist?

Albuterol Signup and view all the answers

What is the role of monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) in relation to endogenous adrenergic drugs?

They metabolize the drugs. Signup and view all the answers

Which class of sympathomimetic drugs increases the levels of endogenous norepinephrine?

Mixed Acting Sympathomimetic Drugs Signup and view all the answers

Which of the following adrenergic receptors is primarily affected by the direct acting sympathomimetic drug isoproterenol?

β1 Signup and view all the answers

Study Notes

Introduction to Autonomic Pharmacology

The autonomic nervous system (ANS) maintains homeostasis, regulating nearly every organ system in the body.
Autonomic drugs make up 10-15% of the top 200 drugs.
Drugs that aren't autonomic can still affect the ANS, sometimes causing adverse effects.

Divisions of the Nervous System

The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS).
The PNS is further divided into the somatic nervous system and the autonomic nervous system.
The somatic system controls skeletal muscles and is a one-neuron system, releasing acetylcholine at the neuromuscular junction.
The autonomic system controls smooth muscle, cardiac muscle and glands; composed of two neuron systems with preganglionic and postganglionic neurons.

The Autonomic Nervous System (ANS)

The ANS has two major divisions: parasympathetic and sympathetic.
The parasympathetic system (craniosacral) has long preganglionic and short postganglionic nerves, synapsing near the effector organ, typically releasing acetylcholine. Its role is to conserve energy ("rest and digest").
The sympathetic system (thoracolumbar) has short preganglionic and long postganglionic nerves, synapsing in ganglia near the spinal cord, typically releasing norepinephrine. These responses are associated with the "fight or flight" response.
The two divisions often have opposing roles in controlling the same target organs in the body.

Properties of the ANS

Involuntary (automatic) control.
Two-neuron system (pre- and postganglionic neurons).
Preganglionic nerves originate in the CNS and terminate in ganglia.
Sympathetic division originates in the thoracic and lumbar regions.
Parasympathetic division originates in the cranial and sacral regions.
Synapses occur in ganglia; the sympathetic uses the paravertebral (and prevertebral) ganglia, while the parasympathetic uses terminal ganglia.
Postganglionic nerves are non-myelinated and innervate effector cells at the neuroeffector junction.

Peripheral Nerve Innervation of Effectors

Autonomic nerves innervate effector organs through two neuron systems (pre- and postganglionic).
The preganglionic neuron releases acetylcholine.
The postganglionic neuron releases either acetylcholine (parasympathetic) or norepinephrine (sympathetic).

Peripheral Location of Autonomic Receptors (Drug Targets)

Acetylcholine receptors affect effector organs involved in processes like controlling the eye, heart, gut-bladder, lung etc.
Norepinephrine receptors affect similar organs, but have an opposing effect to parasympathetic effects on those organs.

Sites of Neurotransmitter Action

Acetylcholine acts at neuromuscular junctions, parasympathetic ganglia, sympathetic ganglia, and parasympathetic and sympathetic neuroeffector junctions.
Norepinephrine acts primarily at most sympathetic neuroeffector junctions, while epinephrine is released from chromaffin cells in the adrenal gland.

Location of Autonomic Receptors

Nicotinic receptors are located in parasympathetic and sympathetic ganglia, chromaffin cells, and skeletal muscle.
Muscarinic receptors are located in effector organs innervated by postganglionic parasympathetic nerves and in some postganglionic cholinergic fibres of the sympathetic system (e.g. sweat glands).
a and β adrenergic receptors are located on most effector organs innervated by postganglionic sympathetic nerves.

Direct effects of autonomic nerve activity

Autonomic effects are generally similar for agonists and antagonists affecting the same systems.

Patterns of autonomic innervation of effector organs

Some organs, for example the heart and blood vessels, have dual opposing innervation from both the sympathetic and parasympathetic system
Others are innervated by sympathetic nerves but have little to no parasympathetic innervation, or vice-versa.

Cholinergic Agonists & Antagonists

Cholinergic agonists mimic acetylcholine's action.
Cholinergic antagonists block acetylcholine's action.

Cholinergic Agonists and Antagonists

Cholinergic agonists can be choline esters (acetylcholine, methacholine, carbachol, and betanechol) or naturally occurring alkaloids (muscarine, arecoline, pilocarpine) , or more synthetic ones like cevimeline.
Cholinergic antagonists include atropine, scopolamine, and others.

Cholinesterase Inhibitors

Acetylcholinesterase breaks down acetylcholine, thus limiting its effect. Inhibitors prolong the effect at target organs and tissues.
Butyrylcholinesterase is found in plasma and on platelets and breaks down choline esters.

Mechanism of Action of Cholinesterase Inhibitors

Direct acting agonists bind to and activate muscarinic and nicotinic receptors.
Indirect acting inhibitors inhibit acetylcholinesterase, prolonging acetylcholine effects at the neuroeffector junction.

Pharmacological Effects of Cholinesterase Inhibitors

Cholinesterase inhibitors cause similar effects to muscarinic agonists (e.g., eye, heart, gut-bladder, lung)
They can also cause unique systemic effects from nicotinic actions, such as muscle fasciculations, tremor, and depolarizing block.

Therapeutic Use of Cholinesterase Inhibitors

Myasthenia Gravis (MG) treatment.
Reversal of neuromuscular blockade (e.g., after surgery).
Antidote for atropine poisoning.
Alzheimer's disease.

Adverse Effects of Cholinesterase Inhibitors

Similar to muscarinic receptor agonists: ocular effects (miosis), respiratory effects (bronchoconstriction), cardiovascular effects (bradycardia), GI effects (diarrhea), genitourinary effects (urination), and diaphoresis.
Can cause a cholinergic crisis when used at high doses.

Parasympatholytics (Anticholinergics)

Drugs that reduce or inhibit parasympathetic actions.
Muscarinic receptor antagonists.
Ganglionic blocking drugs.

Mechanism of Action of Parasympatholytics

Competitive antagonism of muscarinic receptors; blocking the actions of acetylcholine.

Ocular Effects of Atropine

Iris muscle relaxation (mydriasis); the pupil dilates.
Cycloplegia (loss of accommodation). The eye loses the ability to change its focus, usually for near vision.
Decreased lacrimal secretions (dry eyes).

Cardiovascular Effects of Atropine

Tachycardia (increased heart rate).
Mild increase in force of atrial contraction.

Respiratory Effects of Atropine

Bronchodilation.
Inhibition of respiratory tract secretions.
Decreased ciliary mucous clearance.

GI Effects of Atropine

Xerostomia (dry mouth).
Reduced gastric acid secretion.
Reduced GI motility.

Genitourinary Effects of Atropine

Impaired micturition (difficulty urinating).
Blockade of detrusor contraction.
Contraction of trigone and urinary sphincter muscles.

CNS Effects of Atropine

Effects in low or medium doses include effects like sedation, while high doses can cause effects like excitement, hallucinations, delirium, and amnesia.

Other Effects of Atropine

Inhibition of sweat gland secretion.

Drugs for Overactive Bladder/Incontinence

M3-muscarinic cholinergic receptor antagonists: Oxybutynin, Darifenacin, Solifenacin, Tolterodine, Trospium.

Therapeutic Uses of Muscarinic Cholinergic Antagonists in the CNS

Motion sickness prophylaxis (Scopolamine).
Parkinson's disease (Benztropine).
Antidotes for organophosphate poisoning.

Therapeutic Uses of Muscarinic Cholinergic Antagonists in the Periphery

Respiratory disorders (e.g., asthma). Surgical adjuncts, ophthalmologic examinations, treatment of diseases like irritable bowel.

Adverse Effects of Muscarinic Cholinergic Antagonists

Ocular: blurred vision.
Cardiovascular: tachycardia.
Gastrointestinal (GI): xerostomia, constipation, and dyspepsia.
CNS effects can include sedation, excitement, hallucinations, delirium, and amnesia

Overview of Adrenergic Agonists

These agents mimic the actions of the sympathetic nervous system.
Types include: directly acting, indirectly acting, and mixed acting sympathomimetics.
Examples of these sympathomimetic agents include epinephrine, norepinephrine, isoproterenol, phenylephrine, brimonidine, clonidine, dobutamine, albuterol, and others.

Overview of Adrenergic Antagonists

These agents block the actions of the sympathetic nervous system.
Adrenergic receptor blockers (block receptors), and adrenergic neuron blockers.
Examples of these antagonists include carvedilol, propranolol, metoprolol, atenolol, terazosin, prazosin, and others.

Mechanism of Action of a Blockers

Competitive antagonism of alpha 1 adrenergic receptors.
Effects on sympathetic nerve-mediated vasoconstriction.

Therapeutic Use of Alpha Blockers

Hypertension
Benign Prostatic Hyperplasia (BPH)
Peripheral Vascular Disease (PVD) like Raynaud's phenomenon
Impotence.

Adverse Effects of Alpha Blockers

Orthostatic hypotension
Reflex tachycardia and palpitations
Fluid retention and edema
Inhibition of ejaculation
Dizziness, drowsiness, constipation, and diarrhea.

Therapeutic use of Beta Blockers

Hypertension
Angina Pectoris
Arrhythmias
Chronic Congestive Heart Failure (CHF)
Glaucoma
Muscle tremor.

Adverse effects of β Blockers

Central nervous system (CNS) effects: lethargy, depression, fatigue, vivid dreams.
Respiratory effects: wheezing and bronchoconstriction.
Cardiac effects: Cardiac suppression, bradycardia, AV node block.
Rebound effects (angina, hypertension, arrhythmias) with acute drug withdrawal.

Other Sympathomimetic Drugs

Indirect Acting —Release of norepinephrine from sympathetic nerves (e.g., tyramine, amphetamine, methylphenidate, phenentermine).
Block the neuronal uptake of norepinephrine (e.g., tricyclic antidepressants, cocaine, serotonin and norepinephrine reuptake inhibitors).
Mixed Acting —Both direct and indirect action (e.g., ephedrine, pseudoephedrine).

NE Releasing Drugs and MAO Inhibitors

Drugs that release NE from nerves often interact dangerously with MAO inhibitors.
Overuse/abuse can cause dangerous, even life-threatening, responses.

Summary of adrenergic agonists and antagonists

Sympathomimetic (agonist): Mimic sympathetic effects.
Adrenergic blocking (antagonist): Block sympathetic effects.
Mechanism of action relies on receptor binding (either activating or blocking), causing either direct or indirect effects.

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Test your knowledge on sympathomimetic drugs, including their mechanisms, effects, and interactions. This quiz covers critical concepts related to neurotransmitters, drug classifications, and the sympathetic and parasympathetic nervous systems. Perfect for students of pharmacology or health sciences.