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6. Basis for drug action in the ANS
Pharm
52
Nursing
Graduate
08/07/2012

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Term

Adrenergic 


Sympathetic Nervous System (SNS)

Definition

·        Adrenergic - any structure or mechanism which is related to the presence or action of norepinephrine (NE) or epinephrine (Epi) as transmitters. Includes drugs and transmitters which act at adrenergic receptor sites 

Term

Adrenergic nerve fibers


 Sympathetic Nervous System (SNS)

 

Definition
those fibers that synthesize, store, and release NE
Term

Adrenergic receptors


 Sympathetic Nervous System (SNS)

 

Definition

·        Adrenergic receptors - receptors that engage NE or Epi.  They include Alpha 1, Alpha 2, Beta 1, and Beta 2 receptors

Term

Sympathomimetic agents and action


Sympathetic Nervous System (SNS) 

Definition

·        Sympathomimetic agents and action - drugs and transmitters that reproduce a SNS effect 

Term

Sympatholytic agents and actions


Sympathetic Nervous System (SNS) 

Definition

·        Sympatholytic agents and actions - any agent or mechanism that interferes with the normal activity of the SNS

Term

Cholinergic


Parasympathetic Nervous System (PNS) 

Definition

·        Cholinergic - any structure or mechanism that is related to the presence or action of acetylcholine as a transmitter, also drugs which act at cholinergic receptor sites 

Term

Cholinergic nerve fibers


 Parasympathetic Nervous System (PNS)

 

Definition

·        Cholinergic nerve fibers - those fibers that synthesize, store and release acetylcholine

Term

Cholinergic receptors 


Parasympathetic Nervous System (PNS)

Definition

·        Cholinergic receptors - receptors that engage acetylcholine.  They include nicotinic and muscarinic receptors. 

Term

Parasympathomimetic (Cholinomimetic) agents and actions


Parasympathetic Nervous System (PNS) 

Definition

·        Parasympathomimetic (Cholinomimetic) agents and actions - drugs and transmitters that produce a PNS response 

Term

Parasympatholytic (Cholinolytic) agents and actions


Parasympathetic Nervous System (PNS) 

Definition

·        Parasympatholytic (Cholinolytic) agents and actions - any agent or mechanism that interferes with the normal activity of the PNS 

Term

The Efferent division of the peripheral nervous system consists of:

Definition

·        Somatic nervous system

·        Autonomic nervous system (ANS)

Term
The autonomic nervous system (ANS)
Definition

controls the visceral functions of the body. It is often referred to as the vegetative or involuntary nervous system. It is activated mainly by centers in the spinal cord, brainstem and hypothalamus.

The ANS regulates:

the heart,
smooth muscles: lungs, vasc, GI 

secretions

Term
anticholinesterase
Definition
a drug or chemical that inhibits or inactivates the enzyme cholinesterase, resulting in the actions produced by the accumulation of acetylcholine at cholinergic sites. eg, certain nerve gases, which blocks nerve impulses by inhibiting anticholinesterase Examples Insecticides–eg, parathion, and nerve gas agents–eg, sarin, soman, tabun; AChEs can be reversible or irreversible Action Eyes–hyperemia and pupillary constriction, GI tract—↑ GI contractions and secretion of gastric acid
Term
cholinesterase
Definition
an enzyme that acts as a catalyst in the hydrolysis of acetylcholine to choline and acetate. It provides the off mechanism during cholinergic neurotransmission.
Term
acetylcholine
Definition
is released at the ends of nerve fibers in the somatic and parasympathetic nervous systems and is involved in the transmission of nerve impulses in the body.
Term

ANS

/\

/  \

/    \

PNS     SNS

Definition

ANS- Regulate heart, smooth muscles (lungs, vasc, GI), & secretions

 

PNS- rest & digest

 

SNS - fligh or fight

Term
Function of PNS: Rest & digest
Definition

•Slows heart rate

•Increases gastric secretions

•Empties bladder & bowel

•Focuses eye for near vision

•Constricts pupil

•Constricts bronchi

Term
Functions of the SNS: fight or flight
Definition
  • increases HR
  • increases BP 
  • Shunts blood from skin & viscera to skeletal muscles
  • Dilated bronchi
  • Mobilizes energy stores- from liver,releases glycogen
  • eyes dilate (must be able to see far)
Term
[image]
Definition

SNS -thoracolumbar region

-Preganglionic fibers (short) 

-postganglionic fibers (long)


-Each pre fiber connects with>200 post fibers in the paravertebral chain.

 

-SNS activation is widespread, important for "flight/fight"


Term
[image]
Definition

PNS-brain/sacrum

-Preganglionic fibers (long) 

-postganglionic fibers (short)


-Each pre fiber connects connects with only a few post fibers.

 

-PNS activation are highly localized and specific, it never discharges as a complete system.  mediates "rest and digest" functions.

Term

all preganglionic fibers (both SNS and PNS) release ______  which binds to ______receptors located in the ganglia.  


All PNS postganglionic fibers also release Ach, but the Ach released by these postganglionic fibers binds to muscarinic receptors located in the target cells.  


 

Definition
all preganglionic fibers (both SNS and PNS) release acetylcholine (Ach) which binds to nicotinic receptors located in the ganglia.   
Term
Most all SNS postganglionic fibers release norepinephrine There are two exceptions:  
Definition

 (a) postganglionic fibers that supply the sweat glands release Ach, 


(b) the adrenal glands release epinephrine in response to stimulation by SNS preganglionic fibers. 

Term
[image]
Definition

1. Na transports into cell& choline hitches a ride

2. acetyl co-enzyme A catalyzed RXN-->adds acetyl group, turns it into acetylcholine

3. packaged into vesicles

4. Ca channels opened by depolarizing currents, vesicle moves into synapse by exocytosis mediated by Ca

5vesicle move from cytoplasm close to synaptic terina

6. Ach no binds to nicotini/muscarinic receptor

7. biodegreade. cholinesterase biodegrades ach into choline & acetate.

8. choline is recyled & taken up by neuron

9. Binds to

  • a) post-synaptic receptor to cause an action
  • b) neuron from which it was just release to stop    the release of more Ach. Causes opening of K channel which facilitates repolarization
  • c) biodegrades & is recyled

 

Term
[image]
Definition
Term
[image]
Definition
Term
[image]
Definition

tyrosine--> dopa--> dopamine--> and converted by an exzyme.

 

1. dopamine sequestered inot vesicel & becomes NE.

2. influx of ca causes release

4. NE:

a. binds to post synaptic receptor, which is activated.

b. metabolized by COMT excreted in urine

c. reuptake

d. binds to presynaptic receptors to open K channel.

Term
Nicotinic receptors
Definition

are found in 3 locations: 

(a) ANS ganglia (A group of nerve cells forming a nerve center, especially one located outside the brain or spinal cord)

(b) adrenal medulla secretory cells (makes catecholamines ex:

(c) skeletal muscle. 


 Nicotinic receptors function as ligand-gated ion channels, and their activation regulates the flow of ions into and out of cells. 

Term
Muscarinic receptors
Definition
are found in all effector cells stimulated by the postganglionic neurons of the PNS, as well as in sweat glands stimulated by SNS postganglionic cholinergic neurons 
Term
Catecholamines
Definition

Family of neurotransmitters containing dopamine, norepinephrine and epinephrine, produced and secreted by cells of the adrenal medulla in the brain. Catecholamines have excitatory effects on smooth muscle cells of the vessels that supply blood to the skin and mucous membranes and have inhibitory effects on smooth muscle cells located in the wall of the gut, the bronchial tree of the lungs, and the vessels that supply blood to skeletal muscle. There are two different main types of receptors for these neurotransmitters, called alpha and beta adrenergic receptors. The catecholamines are therefore are also known as adrenergic neurotransmitters


a group of substances derived from tyrosine that act as hormones to stimulate cellular activity and carry nerve impulses through the body.

Term

FACTS

Ach activates two types of receptors, nicotinic and muscarinic


Ach molecules are stored in vesicles in the cytoplasm and released in response to calcium influx. 


Ach disengages from the receptor and undergoes enzymatic hydrolysis by acetylcholinesterase.  


Muscarinic receptors all belong to the family of G-protein coupled receptors.

Definition

Let's clarify some terminology before discussing drugs that act on the PNS.

Drugs that we commonly refer to as "cholinergics" and "anticholinergics" are really muscarinic receptor agonists and antagonists. Theoretically, anticholinergic drugs block both nicotinic and muscarinic receptors. But when the term "anticholinergics" is used, it generally refers to drugs that block receptors at effector organs (muscarinic) not receptors at the ganglia (nicotinic).  

Term
Muscarinic Agonist Prototype: Bethanechol
Definition
•A selective muscarinic agonist

•Binds to M3 receptors

•Indicated for urinary retention in postoperative or postpartum patients

•Causes bladder muscle contraction and sphincter relaxation

•AEs include: salivation, lacrimation, bronchospasm, diarrhea, & bradycardia

Term
Muscarinic agonists have limited clinical utility.  And when you consider the effects of PNS stimulation, this makes sense.  If we gave someone an M3 agonist, we'd be stimulating salivation, lacrimation, defecation, urination, and sweating (I think I once went on a blind date with a guy who took an M3 agonist).  Since these usually aren't desirable clinical outcomes, we only use muscarinic agonists for two reasons: 
Definition
to manage glaucoma (prototype drug is pilocarpine) and to induce urination and GI peristalsis (prototype drug is bethanechol).  
Term
Muscarinic antagonists 
Definition

reversibly block Ach binding to muscarinic receptors.  Because they block PNS output, they tip the ANS balance in favor of the SNS.  Therefore, a muscarinic antagonist will have effects that are similar to an adrenergic agonist.  These effects include increased heart rate, bronchodilation, decreased GI peristalsis, inhibition of urination, and mydriasis (pupillary dilation).

 

The clinical uses of anticholinergic agents can be summarized as follows:

1.      Bradycardia - increase heart rate and cardiac output (atropine)

2.      Asthma and bronchitis - induce bronchodilation (ipratropium)

3.      Anesthesia adjunct - reduce secretions (atropine, scopolamine)

4.      Peptic ulcer disease and IBS - decrease GI motility (propantheline, glycopyrolate)

5.      Motion sickness - reduction of vestibular disturbance (scopolamine)

6.      Induction of mydriasis (atropine, cyclopentolate) 

Term

Muscarinic Antagonist Prototype: Atropine

 

Definition

 

•A nonselective competitive muscarinic agonist

•Indicated for

–Bradycardia

–Pupil dilation for eye exams

–GI hypermotility

•Contraindications

–Glaucoma

–Urinary retention

–Tachycardia

Term
Muscarinic Antagonist: side effects
Definition
  • Hyperthermia - because Ach binds to muscarinic receptors in sweat glands and induces sweating
  • Anhidrosis
  • Dry mouth
  • Blurred vision
  • Sedation, amnesia, delirium hallucinations, convulsions
  • Constipation
  • Urinary retention
Term
antimuscarinic drugs (also referred to as anticholinergics or parasympatholytics) such as atropine, cyclopentolate, homatropine, hyoscine and tropicamide inhibit the action of acetylcholine at muscarinic receptors. 
Definition
Term
Muscarinic agonist
Definition
s an agent that enhances the activity of the muscarinic acetylcholine receptor. The muscarinic receptor has different subtypes, labelled M1-M5, allowing for further differentiation.
Term
Muscarinic antagonist
Definition

muscarinic receptor antagonist is an agent that reduces the activity of the muscarinic acetylcholine receptor. Acetylcholine (often abbreviated ACh) is a neurotransmitter, whose receptor is a protein found in synapses and other cell membranes. Besides responding to their primary neurochemical, neurotransmitter receptors can be sensitive to a variety of other molecules. Acetylcholine receptors are classified into two groups based on this:

  • muscarinic, which respond to muscarine
  • nicotinic, which respond to nicotine
Term
Nicotinic agonist
Definition

s a drug which enhances the action at the nicotinic acetylcholine receptor (nAChR).

Examples include:

  • nicotine (by definition—the "nicotinic acetylcholine receptor" is named for its affinity for nicotine)
  • acetylcholine, the endogenous agonist of nAChRs
  • choline
Term
Nicotinic antagonist
Definition
is a type of anticholinergic that inhibits the action at nicotinic acetylcholine receptors. These compounds are mainly used for peripheral muscle paralysis in surgery, but some centrally acting compounds such as bupropionmecamylamine, and 18-methoxycoronaridine block nicotinic acetylcholine receptors in the brain and can be used for treating drug addiction.
Term

Depolarizing Neuromuscular Blocking Drugs


The only depolarizing neuromuscular blocker currently in clinical use is succinylcholine

  Succinylcholine binds to Nm receptors on the motor end-plate and induces depolarization.  However, unlike Ach which rapidly dissociates from the Nm receptor, succinylcholine remains bound and prevents the end-plate from repolarizing.  Thus, the end-plate is in a state of constant depolarization, resulting in muscular paralysis.  

Definition
Succinylcholine has a short duration of action (4-6 minutes) because it is rapidly metabolized by a plasma enzyme called pseudocholinesterase.  As a result, it isn't necessary to administer a drug to reverse its effects.   However, if we administered a cholinesterase inhibitor (as we do to reverse nondepolarizing blockers), we would increase succinylcholine's duration of action.  This is because a cholinesterase inhibitor would inhibit pseudocholinesterase and inhibit succinylcholine's metabolism. 
Term

Nondepolarizing Neuromuscular Blocking Drugs


These drugs are reversible antagonists of nicotinic receptors.  As such, they can bind to Nm receptors, thus blocking depolarization of skeletal muscle fibers and producing motor paralysis.  However, they can also bind to Nn receptors in ganglia and produce autonomic effects.  The major autonomic effect is hypotension (because blocking Nn receptors in SNS ganglia causes arterial vasodilation).  Nondepolarizing blocking drugs can be reversed by administering cholinesterase inhibitors.  

Definition
This makes sense because cholinesterase inhibitors increase the availability of Ach in the synaptic cleft.  Because nondepolarizing blockers are reversible Nm antagonists, their effects can be overcome by increasing the concentration of Ach.  To minimize the muscarinic effects associated with cholinesterase inhibitors, atropine (a muscarinic antagonist) is often concomitantly administered.
Term
Cholinesterase Inhibitors
Definition

Cholinesterases have anticholinergic effects


2.Anticholinesterases have cholinergic effects and can be used as toxic agents i.e., sarin, organophosphate insecticides.  Toxic effects reflect muscarinic activation and include:

 

Eyes: miosis, blurred vision, ciliary spasm

Respiratory:bronchoconstriction

GU: involuntary urination

GI:defecation, cramps, N&V

CV: bradycardia

Secretions: sweating and salivation

 

Cholinesterase inhibitors are used for the following: 

·    to reverse neuromuscular blockade induced by

nondepolarizing agents

·    to improve muscle strength in myasthenia gravis

·    to manage gastroesophageal reflux (i.e., Reglan)

·    to treat glaucoma 

Term
Adrenergic receptors (remember, adrenergic neurons release NE or Epi) can be classified into the following subtypes:
Definition
alpha1, alpha2, beta1, and beta2
Term


Epinephrine binds to all four adrenoceptors


Epinephrine has a greater affinity for beta than alpha receptors

Definition

 

NE binds to alpha1, alpha2, and beta1

 

 

NE has a greater affinity for alpha than beta receptors

Term
Alpha 1 Receptors
Definition

Located in:

–Eyes (produce mydriasis)

–Blood vessels (vasoconstriction)

–GU (ejaculation, prostate contraction)

–Bladder base, urethral sphincter (smooth muscle contraction)

Prototypic agonist is phenylephrine

–Used to induce pupillary dilation

Term
Alpha 1 Receptors
Definition

Prototypic antagonist is prazosin

–Used to manage HTN

–Used to manage BPH

Term
Alpha 2 Receptors 
Definition

Located in:

–Presynaptic nerve terminals (inhibit neurotransmitter release)

–Blood vessels (vasoconstriction)

Prototypic agonist is clonidine

 

Term
Clonidine: Antihypertensive Mechanisms
Definition

Inhibits NE release (NE can bind to alpha 1 and cause vasoconstriction)

Inhibits sympathetic outflow in CNS

Term
Beta 1 Receptors (1 heart)
Definition

Located in heart

–Increase cardiac rate (chronotropic effects)

–Increase force of contraction (inotropic effects)

Prototypic agonist is isoproterenol

–nonselective beta agonist

–used for bronchodilation (beta 2)

–used as cardiac stimulant

Term
Beta 1 Receptors
Definition

Prototypic antagonist is metoprolol

–Heart: reduces rate and force of contraction; inhibits impulse conduction

–Kidney: suppresses renin secretion

Used to manage HTN: Mechanisms

–Reduced cardiac output

–Reduced renin release

–Reduced sympathetic output in CNS

Term
Beta 2 Receptors (2 lungs)
Definition

Prototypic agonist is terbutaline

 

Lungs: Bronchodilation

Used to manage asthma

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