Download N receptors

Pharmacology of efferent
nervous system
Shi-Hong Zhang (张世红), PhD
Dept. of Pharmacology,
School of Medicine, Zhejiang University
[email protected]
Nervous System
Peripheral
Nervous
System (PNS)
Central
Nervous
System (CNS)
Organization
of the nervous system
Peripheral
Nervous
System (PNS)
Efferent
Division
Autonomic
System (ANS)
Afferent
Division
Somatic
System
Parasympathetic
Sympathetic
Enteric
The Enteric Nervous System (+SNS/PSNS)
Sympathetic stimulation causes:
•
•
•
•
•
•
stimulates heartbeat
raises blood pressure
dilates the pupils
dilates the trachea and bronchi
stimulates the conversion of liver glycogen into glucose
shunts blood away from the skin and viscera to the
skeletal muscles, brain, and heart
• inhibits peristalsis （蠕动） in the gastrointestinal (GI)
tract
• inhibits contraction of the bladder and rectum
Parasympathetic stimulation causes:
• slowing down of the heartbeat
• lowering of blood pressure
• constriction of the pupils
• increased blood flow to the skin and viscera
• peristalsis of the GI tract
Nervous System
Peripheral
Nervous
System (PNS)
Efferent
Division
Central
Drugs that produce their
Nervous
System (CNS) primary therapeutic effect by
Afferent
Division
mimicking or altering the
functions of autonomic
nervous system are called
Autonomic
System (ANS)
Somatic
System
autonomic drugs.
Parasympathetic
Sympathetic
Enteric
Organization of the nervous system
Neurotransmitters
• Synthesis
• Storage
• Release
• Degradation
Receptors
• Activation
• Blockade
Drug actions and classification
(1) Mimetics
- direct-acting: receptor agonists
- indirect-acting: increasing amounts and/or
effects of transmitters
(2) Antagonists
- direct-acting: receptor antagonists
- indirect-acting: decreasing amounts and/or
effects of transmitters
Autonomic Pharmacology
• Cholinergic Pharmacology
• Adrenergic Pharmacology
CASE STUDY
• In mid-afternoon, a coworker brings 43-year-old JM to
the emergency department because he is unable to
continue picking vegetables. His gait is unsteady and he
walks with support from his colleague. JM has difficulty
speaking and swallowing, his vision is blurred, and his
eyes are filled with tears. His coworker notes that JM
was working in a field that had been sprayed early in the
morning with a material that had the odor of sulfur.
Within 3 hours after starting his work, JM complained of
tightness in his chest that made breathing difficult, and
he called for help before becoming disoriented.
Cholinergic Terminal
• Choline Uptake→
• ACh Synthesis
Choline + AcCoA → ACh
ChAT
• ACh Storage
• ACh Release
• ACh Effects
- Postsynaptic
- Presynaptic
• ACh inactivation
ACh → Choline + Acetate
AChE
Acetylcholine Release
Regulation
- by autoreceptors
ACh acting on presynaptic m2-cholinergic receptors
- by heteroreceptors
NE acting on presynaptic alpha2-adrenergic receptors
- by metabolism (extraneuronal)
ACh inactivation
Cholinesterases
Acetylcholinesterase is located at cholinergic synapses
and in erythrocytes (does not hydrolyze succinylcholine)
Pseudocholinesterase (synonyms: plasmacholinesterase
or butyrylcholinesterase丁酰胆碱脂酶 ) occurs mainly in
plasma, liver and in glia (hydrolyzes succinylcholine)
Cholinergic Receptors
•
Muscarinic receptors (M receptors)
M1, 3, 5 (smooth muscles); M2, 4(heart)
G-protein Coupled
End Organs
• Nicotinic receptors (N receptors)
NN (N1) receptors; NM(N2 ) receptors
Ligand-gated Ion Channels
NMJ & Ganglia
M receptors :
G-protein
Coupled
Muscarinic
Receptor
Signaling
Pathways
M receptors:
• Depression of the heart (heart rate, conduction)
• Contraction of smooth muscles (sensitive: GI
tract, bronchial, urinary bladder; insensitive: uterine,
blood vascular)
• Exocrine glands (sensitive: sweat, tear, salivary;
insensitive: GI tract);
• Eye (contraction of sphincter muscle of iris: miosis;
contraction of ciliary muscle睫状肌: contraction for
near vision)
Cholinergic Vasodilation
•
The response of an isolated blood vessel to ACh depends on
whether the endothelium is intact (unrubbed) or missing
•
When the endothelium is present, ACh causes smooth muscle
relaxation by stimulating the production of nitric oxide (NO) in
the endothelium
•
In the absence of the endothelium, a small amount of
vasoconstriction is observed
N receptors
• NN receptors（ N1 receptors ）
- Sympathetic and parasympathetic ganglia
- Adrenal medulla
• NM receptors （N2 receptors ）
- The Neuromuscular Junction (NMJ)
(Contraction of skeletal muscles)
N receptors : Ligand-gated Ion Channels
• At the NMJ, N receptors
pentameric with four
types of subunits, two a
subunits bind ACh for
ligand gating
• All other nAChRs,
including those at the
peripheral ganglia,
have 2 a’s and 3 b’s
Ganglionic Neurotransmission
N = Nicotinic AChR
M = Muscarinic AChR
EPSP = Excitatory Postsynaptic Potential
IPSP = Inhibitory Postsynaptic Potential
The Neuromuscular Junction (NMJ)
A
B
Myasthenia Gravis
• This means “serious disorder the NMJ”
• This is an autoimmune disease
• Antibodies against the a subunit of the nAChR
• The ability of ACh to activate the nAChRs is blocked by
the antibodies
• As many autoimmune diseases, stress can make the
symptoms worse
• Treatment is to potentiate cholinergic signaling and to
remove the antibodies (blood dialysis)
Drug classification
1. Cholinomimetics
(1) Direct-acting drugs: Cholinoceptor agonists
M, N receptor agonists: acetylcholine
M receptor agonists: pilocarpine
N receptor agonists: nicotine
(2) Indirect-acting drugs: Cholinesterase inhibitors
(Anticholinesterases)
Reversible: neostigmine新斯的明
Irreversible: organophosphates 有机磷酸酯类
Cholinesterase reactivators: pralidoxime iodide
碘解磷定
Drug classification
2 Cholinergic antagonists
(1) Cholinoceptor antagonists
M cholinoceptor antagonists
atropine (Antimuscarinic drugs)
N cholinoceptor antagonists
NN cholinoceptor antagonists: mecamylamine
(Ganglionic blocking drugs, rarely used)
NM cholinoceptor antagonists: succinylcholine
(Neuromuscular blocking drugs )
(2) Botulinum Toxin (Botox, blocks ACh release)
Cholinomimetics
Direct-acting drugs
Ach derivatives （胆碱酯类）
Natural muscarinic agonists (生物碱类M
受体激动剂)
Nicotinic receptor agonists (N受体激动剂)
ACh Derivatives
Bond
cleaved
by AChE
乙酰胆碱
醋甲胆碱
卡巴胆碱
氯贝胆碱
AChE resistant
ACh Derivatives
Bethanechol 氯贝胆碱is most commonly used, particularly
post-op for the treatment of paralytic ileus and urinary
retention
Natural Muscarinic Agonists
槟榔碱
毛果芸香碱
毒蕈碱
Nicotinic potency
• Arecoline: areca or betal nuts (India,E. Indies)
• Pilocarpine: pilocarpus (S. Amer. shrub)
• Muscarine: amanita muscaria (mushroom)
“Food” Poisoning
•
Poisoning causes muscarinic
overstimulation：
- salivation, lacrimation, visual
disturbances;
Amanita muscaria
- abdominal colic and diarrhea
伞形毒蕈
- bronchospasm and bradycardia
- hypotension; shock
•
Atropa belladonna
颠茄
Treatment is with atropine
Pilocarpine
(1) Eyes
• Miosis (缩瞳): contraction of sphincter muscle of iris
• Lowing intraocular pressure: enlarging angle of anterior
chamber, increasing drainage of aqueous humor
• Spasm of accommodation (调节痉挛): contraction of
ciliary muscle, contraction for near vision
• Ophthalmological 眼科 uses
Glaucoma 青光眼: narrow (closed)- or wide (open)-angles
used for the emergency lowering of intraocular pressure
Iritis: miotics缩瞳药/mydriatics扩瞳药
Ciliary muscle
(dilation)
Canal of Schlemm
mydriasis
zonule
Posterior
chamber
Anterior
chamber
lens
iris
paralysis of
accommodation
far sight
atropine
spasm of
accommodation
miosis
zonule
Anterior
chamber
Ciliary muscle
(contraction)
near sight
pilocarpine
Circulation of aqueous humor
Glaucoma
• Open-angle glaucoma：
disease of the aging eye increased intraocular
pressure, degeneration of
the optic head, and
restricted visual field
• Obstruction of the
aqueous drainage leads to
elevated intraocular
pressure (IOP), and may
result in glaucomatous
damage to the optic nerve
Glaucoma
• Glaucoma management involves lowering IOP by
- Decreasing aqueous production by the ciliary
body
- Increasing aqueous outflow through the
trabecular meshwork and uveal outflow paths
• Pilocarpine: increase aqueous outflow by
contraction of the ciliary muscle to increase tone
and alignment of the trabecular network
Pilocarpine
（2） Promoting secretion of exocrine glands,
especially in sweat, salivary and tear glands
• Systemic use
Antidote解毒剂 for atropine poisoning
• Adverse effects
M-like syndrome
N receptor agonists:
Nicotine
Actions at ganglia, NMJ, brain are complex and frequently
unpredictable, because of the variety of neuroeffector sites
and because nicotine both stimulates and desensitizes
effectors.
Periphery: HR, BP,  GI tone & motility
CNS: stimulation, tremors, respiration, emetic effects
The addictive power of cigarettes is directly related to their
nicotine content.
Drug classification
1. Cholinomimetics
(1) Direct-acting drugs: Cholinoceptor agonists
M, N receptor agonists: acetylcholine
M receptor agonists: pilocarpine
N receptor agonists: nicotine
(2) Indirect-acting drugs: Cholinesterase inhibitors
(Anticholinesterases)
Reversible: neostigmine 新斯的明
Irreversible: organophosphates 有机磷酸酯类
Cholinesterase reactivators: pralidoxime iodide
碘解磷定
Acetylcholinesterase (AChE) Activity
AChE Inhibitors
A. Competitive (reversible)
B. Carbamates (氨甲酰类slowly reversible)
C. Organophosphates (irreversible)
依酚氯铵
These agents are
reversible and are
used medically
(glaucoma or MG)
新斯的明
neostigmine
毒扁豆碱
These agents are
irreversible and
are used as
pesticides or for
glaucoma
Acetylcholinesterase Inhibitors:
Reversible
Edrophonium (依酚氯铵)
Rapidly absorbed;
A short duration of action (5-15min);
Competitive (reversible)
Used in diagnosis of myasthenia
gravis.
Excess drug may provoke a
cholinergic crisis, atropine is the
antidote.
Other reversible ACHEI: tacrine 他克林, donepezil 多奈哌齐
Acetylcholinesterase Inhibitors: Carbamates
Inhibitory Effects are slowly
reversible
Representative Drugs
neostigmine (quaternary amine 季铵)
pyridostigmine (quaternary amine)
physiostigmine (tertiary amine 叔胺)
quaternary amines effective in periphery only
tertiary amines effective in periphery and CNS
（fat-soluble）
Neostigmine 新斯的明
Pharmacological effects
• AChE(-), ACh release↑, stimulating NMR
• stronger effect on skeletal muscles
• effective on GI tract and urinary bladder
• more polar and can not enter CNS
• relatively ineffective on CVS, glands, eye
Neostigmine
Clinical uses
1.
Myasthenia gravis: symptomatic treatment
overdose: cholinergic crisis
胆碱能危象：大量出汗，大小便失禁，瞳孔缩小，睫状肌痉挛，
心动过缓，低血压，肌无力，呼吸困难
2.
Paralytic ileus 麻痹性肠梗阻urinary retention: post operative
abdominal distension and urinary retention
3.
Paroxysmal superventricular tachycardia（rarely use）
4.
Antidote for tubocurarine ( 筒 箭 毒 碱 ) and related drug
poisoning
5.
Glaucoma
Neostigmine
Adverse effects
• Cholinergic effects: muscarinic and nicotinic effects,
treated with atropine (muscarinic)
• Contraindications：
mechanical ileus（机械性肠梗阻）
urinary obstruction
bronchial asthma
poisoning of depolarizing skeletal muscle relaxants
(e.g. succinylcholine, 琥珀酰胆碱)
Acetylcholinesterase Inhibitors:
Irreversible
Bond is hydrolyzed
in binding to the
enzyme
乙磷硫胆碱
For ophthalmic use
梭曼
Dichlorvos 敌敌畏
对硫磷
对氧磷
Dimethoate 乐果
马拉硫磷
马拉氧磷
Organophosphates
(1) Toxic symptoms
Acute intoxication
• Muscarinic symptom:
eye, exocrine glands, respiration, GI tract, urinary tract,
CVS
• Nicotinic symptoms:
NN: elevation of BP, increase of HR;
NM: tremor of skeletal muscles
• CNS symptoms:
excitation, convulsion; depression (advanced phase)
CASE STUDY
• In mid-afternoon, a coworker brings 43-year-old JM to
the emergency department because he is unable to
continue picking vegetables. His gait is unsteady and he
walks with support from his colleague. JM has difficulty
speaking and swallowing, his vision is blurred, and his
eyes are filled with tears. His coworker notes that JM
was working in a field that had been sprayed early in the
morning with a material that had the odor of sulfur.
Within 3 hours after starting his work, JM complained of
tightness in his chest that made breathing difficult, and
he called for help before becoming disoriented.
Organophosphates
(1) Toxic symptoms
Chronic intoxication
• usually occupational poisoning
• plasma ChE activity ↓,
• weakness, restlessness, anxiety, tremor, miosis, ……
Organophosphates
(2) Detoxication
• Elimination of poison; Supportive therapy
• Antidotes
Atropine－antagonizing muscarinic effects; early,
large dose, and repeated use
Cholinesterase reactivators－reactivation of
phosphated AChE; moderate-severe patients, early use
(More effective on tremor), combined with atropine
– Pyraloxime methoiodide (PAM，碘解磷定)
– Pralidoxime chloride （氯解磷定）: safer than PAM
– Obidoxime chloride（双复磷）: two active oxime
groups
Organophosphates
Pralidoxime （解磷
定）can restore
AChE activity if
administered soon
after toxin exposure.
• Conjugating with
organophosphate by
oxime group;
• Conjugating with free
organophasphates
Why isn’t this ACHEI pesticide neurotoxic to humans?
Malathion马拉硫磷
Insects and mammals metabolize the ‘prodrug’ differently
Insects - P450 metabolism: P-S bond converted to P-O bond:
now, the molecule, malaoxon, is an active inhibitor
Mammals – esterase activity: hydrolyzes the molecule into
inactive metabolites
Summary: ACHEI Applications
Pharmacological Actions: Increases ACh concentrations
at cholinergic synapses, thereby increasing cholinergic
activity.
 glaucoma (e.g. physiostigmine毒扁豆碱, echothiophate乙磷硫胆碱 )
 myasthenia gravis (e.g. Edrophonium, neostigmine, pyridostigmine )
 reverse neuromuscular blockade from competitive
antagonists (neostigmine)
 Alzheimer’s disease (tacrine & donepezil, galanthamine)
 chemical warfare agents
 insecticides
Drug classification
2 Cholinergic antagonists
(1) Cholinoceptor antagonists
• M cholinoceptor antagonists
–
atropine (Antimuscarinic drugs)
• N cholinoceptor antagonists
–
NN cholinoceptor antagonists: mecamylamine
(Ganglionic blocking drugs, rarely used)
–
NM cholinoceptor antagonists: succinylcholine
(Neuromuscular blocking drugs )
• Botulinum Toxin (botox, blocks ACh release)
Muscarinic Antagonists
(Antimuscarinic drugs)
Tertiary amines（叔铵）
Quaternary amines（季铵）
东莨菪碱
异丙托铵
噻托溴铵
Atropa belladonna
颠茄
Datura sp.
洋金花
Datura stramonium
曼陀罗
Henbane Seed
山莨菪
Atropine
1. Pharmacological effects
(1) Inhibition of exocrine gland secretion
salivary, sweat glands
tear, respiratory tract glands
relatively ineffective: GI tract
(2) Eye
mydriasis 瞳孔散大
rise in intraocular pressure
paralysis of accommodation调节麻痹
Ciliary muscle
(dilation)
Canal of Schlemm
mydriasis
zonule
Posterior
chamber
Anterior
chamber
lens
iris
paralysis of
accommodation
far sight
atropine
miosis
spasm of
accommodation
zonule
Anterior
chamber
Ciliary muscle
(contraction)
near sight
pilocarpine
Atropine
1. Pharmacological effects
(3) Antispasmodic action on smooth muscle
• sensitive: GI, urinary bladder (spasmodic state)
• relatively insensitive: bile duct, urinary tract,
bronchial tract
• insensitive: uterus
Atropine
1. Pharmacological effects
(4) Cardiovascular system: dose dependent
•
•
•
Lower therapeutic doses: HR↓(bradycardia); Blood
vessels and blood pressure: no effect
Moderate to high therapeutic doses / high vagal tone:
HR↑ (tachycardia); A-V conduction ↑
Larger doses: cutaneous vasodilatation
(5) CNS stimulation：
•
sedation, memory loss, psychosis (high dose)
Atropine
2. Clinical uses
(1) Ophthalmology
Measurement of the refractive errors (屈光不正): children
Acute iritis or iridocyclitis: mydriatics/miotics
(2) Antispasmodic agent
GI, biliary or renal colic, enuresis
(3) Inhibiting exocrine gland secretion
Preanesthetic medication麻醉前用药
(4) Bradycardia
sinus or nodal bradycardia, A-V block
(5) Antidote for organophosphate poisoning
(6) Septic shock 感染性休克
Atropine
3. Adverse effects
(1) Side effects dry mouth, blurred vision, “sandy eyes”
(2) toxicity Lethal dose: 80~130 mg (adult), 10 mg (child)
•
Low: xerostomia (dry mouth); anhidrosis (dry skin),
tachycardia
•
Moderate: above plus mydriasis, cycloplegia (睫状肌麻
痹); difficulty speaking, swallowing & urinating; and
hot, red, dry skin
•
High: above plus ataxia, hallucinations幻觉 & delirium
谵妄; coma
Atropine
3. Adverse effects
(3) Detoxication
Supportive treatment
Symptomatic
treatment:
e.g.
diazepam
symptoms.
Antidote: Physostigmine or pilocarpine
(4) Contraindications
glaucoma, prostatauxe 前列腺肥大, fever
for
CNS
Scopolamine东莨菪碱
• Actions and clinical uses
– Peripheral effects are similar to atropine;
but has stronger central effects (depression)
– Pre-anesthetic medication, prevention of
motion sickness, Parkinson’s disease
Anisodamine (654-1,2)
• Actions and clinical uses
– Peripheral effects, similar to atropine; lower
toxicity
– Septic shock and visceral colic (relieve
spasm of vascular smooth muscles)
Synthesized surrogates
• Tropicamide 托吡卡胺: mydriatic, cycloplegic
shorter duration (1/4 day)
• Propantheline 丙胺太林，普鲁本辛
poor absorption (po) and BBB penetration
•
•
•
•
antispasmodic effects in GI, treatment of peptic ulcer
Ipratropium 异丙托铵: asthma
Benztropine 苯托品: Parkinson’s disease
Trihexyphenidyl 苯海索
Pirenzepine 哌仑西平：M1 selective, peptic ulcer,
asthma
CASE STUDY
JH, a 63-year-old architect, complains of urinary symptoms
to his family physician. He has hypertension and the last 8
years, he has been adequately managed with a thiazide
diuretic and an angiotensin-converting enzyme inhibitor.
During the same period, JH developed the signs of benign
prostatic hypertrophy, which eventually required
prostatectomy to relieve symptoms. He now complains
that he has an increased urge to urinate as well as urinary
frequency, and this has disrupted the pattern of his daily
life. What do you suspect is the cause of JH’s problem?
What information would you gather to confirm your
diagnosis? What treatment steps would you initiate?
Nicotinic receptor antagonists
NN receptor antagonists
(Ganglionic blocking drugs)
• Acting on sympathetic and parasympathetic
ganglionic cells; reducing blood pressure by
inhibiting sympathetic ganglia ( have been
abandoned for clinical use, due to their lack of
selectivity)
• Short-acting; tachyphylaxis (快速抗药反应)
• Used for treatment of hypertension
─ Trimethaphan(咪噻芬)
– Mecamylamine (美加明)
NM receptor antagonists
(Neuromuscular blocking drugs )
• Two classes:
Depolarizing: succinylcholine 琥珀酰胆碱
Non-depolarizing: drugs act as competitive antagonists
d-tubocurarine 筒箭毒碱
Note: Belong to Skeletal Muscle Relaxants. It is important to
realize that muscle relaxation does not ensure
unconsciousness, amnesia, or analgesia.
NM receptor antagonists
(Neuromuscular blocking drugs )
1. Depolarizing neuromuscular blockers (Non-competitive)
(depolarizing skeletal muscle relaxants)

act as acetylcholine (ACh) receptor agonists
the depolarized membranes remain depolarized and unresponsive
to subsequent impulses (ie, they are in a state of depolarizing block).

not metabolized by AChE
- diffuse away from the neuromuscular junction and are hydrolyzed in
the plasma and liver by pseudocholinesterase (nonspecific
cholinesterase, plasma cholinesterase, or butyrylcholinesterase) and
elimination by kidney
Succinylcholine (Scoline司可林)
acetylcholine
succinylcholine
Succinylcholine is the only depolarizing agent used clinically
(t1/2= 2-4 min).
Properties of actions:
•
•
•
•
•
•
initially transient fasciculations （肌束震颤）
anti-AChE potentiates their effects
tachyphylaxis after repeated uses
no ganglion-blocking effects at therapeutic doses
the drugs are highly polar, poor bioavailability; i.v.
as quaternary compounds, do not enter CNS
Succinylcholine (Scoline)
• Main pharmacological effects
– Transient excitation (fasciculations), and
then inhibition (relaxation)
– Relax Skeletal Muscles in neck, limbs >
face, tongue, throat; less effective on
breath muscles at therapeutic doses
Succinylcholine (Scoline)
• Clinical uses
– An adjuvant in anesthesia or operation
– Intubation of trachea, esophagus, etc.
– Prevention of trauma during electroshock therapy （无抽
搐电休克疗法）
– Contraindicated in awake patients, should use
under anesthesia
Succinylcholine (Scoline)
• Adverse effects
(1) Apnea (respiratory paralysis)
overdose or hypersensitive patients;
neostigmine potentiates the toxic effects
(2) Muscle spasm
muscular pain after operation
Succinylcholine (Scoline)
(3) Elevation of K+ in plasma
contraindicated in patients with a tendency
of hyperkalemia
(4) Malignant hyperthermia
genetic abnormality, treated by dantrolene
(Ca2+ release inhibitor)
(5) Others
rise in intraocular pressure (glaucoma);
histamine release
Genetic Variation: Effects on Duration of
Action of Succinylcholine
• Duration of action is prolonged by high doses or by abnormal
metabolism. The latter may result from hypothermia (decreases
the rate of hydrolysis), low pseudocholinesterase levels, or a
genetically aberrant enzyme.
• Low pseudocholinesterase levels generally produce only modest
prolongation of succinylcholine's actions (2-20 min).
• One in 50 patients has one normal and one abnormal (atypical)
pseudocholinesterase gene, resulting in a slightly prolonged
block (20-30 min).
• Even fewer (1 in 3000) patients have two abnormal genes
(homozygous atypical) that produce an enzyme with little or no
affinity for succinylcholine and have a very long blockade (e.g.,
4-8 h) following administration of succinylcholine.
• Scoline apnea
Succinylcholine (Scoline)
• Drug interactions
- Thiopental （强碱性，可分解scoline）
- ChE inhibitors:
AChE inhibitors, cyclophosphamide,
procaine, etc.
- Some antibiotics:
kanamycin, polymyxins, etc. (synergism in
neuromuscular blocking)
NM receptor antagonists
(Neuromuscular blocking drugs)
2.
Nondepolarizing neuromuscular blockers
(Competitive)
(nondepolarizing skeletal muscle
relaxants)
Tubocurarine (筒箭毒碱)
Reversibly bind to the nicotinic
receptor at the neuromuscular
junction (competitive antagonists)
Tubocurarine
• Effects: competitive blockade of NM receptors
• Uses: adjuvant medication for anesthesia or operations,
eg. tracheal intubation
• Adverse effects:
Respiratory paralysis: can be reversed by neostigmine
Enhancing histamine release: BP , bronchoconstriction,
salivary secretion
Blocking ganglion: BP 
Contraindications: myasthenia gravis, bronchial asthma,
shock, child (< 10 y)
Other nondepolarizing neuromuscular blockers
• Benzylisoquinolines（苄基异喹啉类）
atracurium （阿曲库铵）
doxacurium（多撒库铵）
mivacurium（米库铵）
• Ammonio steroids（类固醇铵类）
pancuronium （潘库铵）
vecuronium（维库铵）
pipecuronium（哌库铵）
rocuronium（罗库铵）
Botulinum Toxin 肉毒杆菌毒素
- Skeletal muscle relaxants
- blocks ACh release from cholinergic terminals
- selective for ACh terminals
- results in irreversible flaccid paralysis (松弛性瘫痪) in
muscles
Acts by cleaving
SNAP proteins →
inhibits ACh release
Botulinum Toxin
- an anaerobic bacillus, clostridium botulinum can multiply in
preserved food
- it synthesizes a protein that can be absorbed (pinocytosis or
transport?) from the GI tract to reach the systemic circulation
- penetrates tissues to reach cholinergic nerve terminals
- then, it is uptaken (pinocytosis) and internalized in vesicles
whose lumen becomes acidified
- the low pH of the vesicles splits the inactive molecule into 2
active enzymes that have proteolysis functions
Botulinum Toxin
Applications
• Strabismus (lack of parallelism of eyes 斜视), blepharospasm
(eyelid spasm), dystonia (abnormal tonicity).
• Excessive sweating
• Cosmetic procedures ( “frown lines” or “crow’s feet”鱼尾纹)
Note: effects can last for ~3-6 months.
参考书目
• 杨世杰主编《药理学》人民卫生出版社2010
第二版
• Katzung BG, Basic & Clinical
Pharmacology (10th edition), 2007.
• Lipincott’s illustrated reviews—
Pharmocology (2nd edition), 2002