Pharmacotherapy of cholinergic agent 台大藥理所 邱麗珠老師

Outlines Cholinergic Transmission Cholinergic Fibers Autonomic pre-gangalionic fibers Parasympathetic postganglionic fibers Somatic motor nerve fibers Cholinergic Receptors Nicotinic：NM、NN Muscarinic：M1、M2、M3、M4、M5

Outlines Cholinergic Pharmacology Muscarinic receptor antagonists Nicotinic receptor antagonists Ganglion blockers Neuromuscular blockers Anticholinesterase Cholinergic receptor agonists

Cholinergic Neurotransmission

Cholinergic Neurotransmission

Cholinergic Neurotransmission Trafficking & mobilization Synapsins & Rab3 Docking Vesicle membrane Synaptotagmin Synaptobrevin (VAMP) Synaptic plasma membrane Neurexins Syntaxins Pore fusion Synaptophysin

Main synaptic location Nicotinic Receptors Receptor (Primary receptor subtype) Main synaptic location Membrane response Molecular mechanism Agonists Antagonists Skeletal muscle (NM) Adult (α1)2β1εδ Fetal (α1)2β1γδ Skeletal NMJ (Post-junctional) Excitatory End-plate depolarization contraction ↑ Cation permeability (Na+、K+) Ach Nicotine Succinylcholine Atracurium Vecuronium d-Tubocurarine Pancuronium α-Bungarotoxin α-Conotoxin Peripheral neuronal (NN) (α3)2(β4)3 Autonomic ganglia Adrenal medulla Depolarization Firing of postganglionic neuron Depolarization & secretion of catecholamines Epibatidine Dimethylphenylpip erazinium (DMPP) Trimethaphan Mecamylamine Central neuronal (CNS) (α4)2(β4)3 (α-Bungarotoxin- insensitive) CNS Pre- and post-junctional Pre- & post- synaptic excitation Pre-junctional control of transmitter release Cytisine Anatoxin A Dihydro-β- erythrodine Erysodine Lophotoxin (α7)5 sensitive) Pre- and post-synaptic (Ca2+) Methyllycaconitine IMI

Nicotinic Receptors

Muscarinic Receptors M1 receptor Cellular & tissue location CNS (Cerebral cortex、Hippocampus、Striatum) Autonomic ganglia Gland (Gastric & salivary)、Enteric nerves Cellular response Activation of PLC ↑ IP3 & DAG → ↑ Ca2+ & PKC Depolarization & excitation (↑ sEPSP) Activation of PLD2、PLA2 →↑ AA Couples via Gq

Muscarinic Receptors M1 receptor Functional response Increased cognitive function (Learning & memory) Increased seizure activity Decrease in dopamine release & locomotion Increase in depolarization of autonomic ganglia Increase in secretions

Muscarinic Receptors M2 receptor Cellular & tissue location CNS、Heart、Smooth muscle、Autonomic nerve terminals Cellular response Inhibition of adenylyl cyclase → ↓ cAMP Activation of inwardly rectifying K+ channels Inhibition of voltage-gated Ca2+ channels Hyperpolarization & inhibition Couple via Gi/Go (PTX-sensitive)

Muscarinic Receptors M2 receptor Functional response Heart SA node Slowed spontaneous depolarization Hyperpolarization、 ↓ Heart rate AV node ↓ Conduction velocity Atrium： ↓ Refractory period & contraction Ventricle：Slight ↓ contraction

Muscarinic Receptors M2 receptor Functional response Smooth muscle ↑ Contraction Peripheral nerves Neural inhibition via autoreceptors & heteroreceptor ↓ Ganglionic transmission CNS Neural inhibition ↑ Tremors Hypothermia Analgesia

Muscarinic Receptors M3 receptor Cellular & tissue location Widely expressed in CNS Abundant in smooth muscle & glands Heart Cellular response Same as M1 receptor

Muscarinic Receptors M3 receptor Functional response Smooth muscle ↑ Contraction (Predominant in bladder) Glands ↑ Secretion (Predominant in salivary gland) ↑ Food intake & body weight & fat deposits Inhibition of dopamine release Synthesis of NO

Muscarinic Receptors M4 receptor Cellular & tissue location Preferentially expressed in CNS (Particularly forebrain) Cellular response Same as M2 receptor Functional response Autoreceptor & heteroreceptor-mediated inhibition of transmitter release in CNS & periphery Analgesia Cataleptic activity Facilitation of dopamine release

Muscarinic Receptors M5 receptor Cellular & tissue location Expressed in low levels in CNS & periphery Predominant mAchR in dopamine neurons in VTA & SNc Cellular response Same as M1 receptor Functional response Mediator of dilation in cerebral arteries & arterioles Facilitates dopamine release Augmentation of drug seeking behavior & reward Opiates、Cocaine

Muscarinic Functions Parasympathomimetic Organ Type Response Eye Sphincter muscle of iris M3 Contraction (Miosis) Ciliary muscle Contraction for near vision Heart Sinoatrial node M2 Decrease in rate (Negative chronotropy) Atria Decrease in contractile strength (Negative Inotropy) Decrease in refractory period Atrioventricular node Decrease in conduction velocity (Negative dromotrophy) Increase in refractory period Ventricles Small decrease in contractile strength

Muscarinic Functions Parasympathomimetic Organ Type Response Blood vessels Arteries M3 Dilation (Via EDRF) Constriction (High-dose direct effect) Veins Lung Bronchial muscle Contraction (Bronchoconstriction) Bronchial glands Stimulation Gastrointestinal tract Motility Increase Sphincters Relaxation Secretion

Muscarinic Functions Parasympathomimetic Organ Type Response Urinary bladder Detrusor M3 Contraction Trigone & sphincter Relaxation Glands Sweat gland Secretion Salivary gland Lacrimal gland Nasopharyngeal gland

Pharmacological effects Muscarinic Antagonists CNS Drowsiness Scopolamine > atropine Excitement、Agitation、Hallucination、Coma Anti-tremor in Parkinson’s disease Reduce motion sickness

Pharmacological effects Muscarinic Antagonists CV system Bradycardia (Low dose) Central vagal stimulation Presynaptic Muscarinic receptor block Disinhibition of Ach release Tachycardia (Intermediate dose) Peripheral vagalytic ↓PR interval in patients with high vagal tone ↓ Atria contractility inhibition, less effect on ventricle ↑Vasotone in skeletal muscle

Pharmacological effects Muscarinic Antagonists Respiratory system Bronchodilation ↓ Bronchosecretion For Asthma & COPD Premedication of general anesthesia Sweat glands ↓ Sweat secretion (Sympathetic cholinergic fibers) Atropine fever Infants & children

Pharmacological effects Muscarinic Antagonists Eye Mydriasis Inhibition of Iris contraction Cycloplegia Loss of lens accommodation Dry eyes ↑ Narrow angle glaucoma

Pharmacological effects Muscarinic Antagonists Gastrointestinal Tract Dry mouth (Low dose) ↓ Gastric secretion (High dose) ↓ GI motility, especially selective M1 antagonist ↓Presynaptic muscarinic excitation ↑ Gastric empty time ↑ Intestinal transit time Genitourinary Tract For neurogenic bladder Precipitating urinary retention Elder men with prostate hyperplasia No effect on uterus

Pharmacological effects Muscarinic Antagonists Tissue sensitivity to Atropine Atropine sensitivity (High to low) Salivary、Bronchial、Sweat glands Smooth muscle Cardiac function Gastric acid secretion

Clinical Considerations Muscarinic Antagonists Contraindication Narrow-angle glaucoma Prostatic hypertrophy Elderly Cognitive impairment Side effect Dry mouth、Blurred vision、Urinary retention、 Fever Sedation、Tachycardia、 Ileus CNS hyperexciation Delirium、Hallucination、Seizures、Agitation

Muscarinic antagonists Atropine ↓ Salivation & mucus secretion Organophosphate intoxication Prolong mydriasis & cycloplegia for eye surgery For symptomatic sinus bradycardia Scopolamine Motion sickness (Transdermal patch) Chemotherapy induced nausea (IV) Methscopolamine、Glycopyrrolate Peptic ulcer GI spasms Prevent bradycardia

Muscarinic antagonists Pirenzepine (M1 selective) Peptic ulcer Ipratropium、Tiotropium (Inhalational) COPD (better than β-agonist) Asthma (not better than β-agonist) Darifenacin、Solifenacin (M3 selective) Less adverse effect Oxybutynin、Propantheline、Tolterodine、Trospium Over-reactive bladder Incontinence Less dry mouth in Tolterodine

Nicotinic antagonists Autonomic Ganglia

Site Predominant tone Effect of ganglionic block Arterioles Sympathetic (Adrenergic) Vasodilation ↑ Peripheral blood flow Hypotension Veins Dilation ↓ Venous return ↓ Cardiac output Heart Parasympathetic (Cholinergic) Tachycardia Iris Mydriasis Ciliary muscle Cycloplegia (Focus to far) Gastrointestinal tract ↓ Tone & motility Constipation ↓ Gastric secretion ↓ Pancreatic secretion Urinary bladder Urinary retention Salivary glands Xerostomia Sweat glands Sympathetic (Cholinergic) Anhidrosis Genital tract Sympathetic & Parasympathetic ↓ Stimulation

Nicotinic antagonists Ganglion Blockers Autonomic ganglia blockers Mecamylamine Trimethaphan Used in hypertension in patient with acute aortic dissection or pulmonary edema Decrease sympathetic reflex Lower blood pressure

Nicotinic antagonists Neuromuscular Junction Miniature endplate potential (0.5-1.2 mV) Spontaneous release、Quantal release Endplate Potential (2~8 mV) Evoked release Action potential (100mV) Muscle contraction

Nicotinic antagonists Neuromuscular Blockers Competitive nicotinic receptor blockers D-tubocurarine、Pancuronium、Gallamine (Long) Vecuronium、Rocuronium (Intermediate) Mivacurium、Atracurium (Short) Depolarization blockers Succinylcholine Decamethonium

Nicotinic antagonists Competitive nicotinic receptor blockers Selective NM antagonist at motor endplate d-Tubocurarine (d-TC) Protodrug：Reversible blocker α-Bungarotoxin Selective irreversible NM antagonist NM receptor occupancy 75-80% occupied：Neuromuscular block >95% occupied：Muscle relaxation Reversed by Anti-ChE Single twitch inhibition & tetanic fade

Nicotinic antagonists Depolarizing blockers Phase 1 Membrane depolarization Muscle contracture No tetanic fade Potentiated by Anti-ChE Phase 2 NM Desensitization, Na+ channel inactivation No depolarization Single twitch inhibition Tetanic fade Reversed by Anti-ChE

Nicotinic antagonists Comparison of neuromuscular blockers D-Tubocurarine Decamethonium Effect of D-Tubocurarine Administered previously Additive Antagonistic Effect of Decamethonium No effect, or antagonistic Some tachyphylaxis, but may addictive Effect of Anticholinesterase agents on block Reversal of block No reversal Effect on motor end plate Elevated threshold to Ach No depolarization Partial Persistent depolarization Initial excitatory effect on striated muscle None Transient fasciculation Character of muscle response to indirect tetanic stimulation during partial block Poorly sustained contraction Well-sustained contraction

Nicotinic antagonists Clinical responses & monitoring of phase I & phase II Response Phase I Phase II End plate membrane potential Depolarized to -55mV Repolarization toward -80mV Onset Immediate Slow transition Dose-dependence Lower Usually higher or follows prolonged infusion Recovery Rapid More prolonged Train of four & tetanic stimulation No fade Fade Acetylcholinesterase inhibition Augments Reverses or antagonizes Muscle response Fasciculation → Flaccid paralysis

Nicotinic antagonists Therapeutic Uses of Neuromuscular Blockers During surgery Muscle relaxation Endotracheal intubation Maintaining controlled ventilation ↓ Muscle fasciculation Nonsurgical uses Myasthenia gravis diagnosis ↓ Muscle spasms Adjunct relaxation during electroshock therapy

Nicotinic antagonists Clinical Considerations of Neuromuscular Blockers (SCh) Pharmacogenomic variation of butyrylcholinesterase Normal metabolizer < 15min Slow metabolizer > 2hr Electrolyte imbalance Malignant hyperthermia during anesthesia Patient states affecting duration Trauma Alcoholism Pregnancy Oral contraceptives Local anesthetics

Nicotinic antagonists Clinical Considerations of Neuromuscular Blockers Drug Interactions Inhalated anesthetics Aminoglycoside antibiotics Ca2+ channel blockers Ca2+、K+、Mg2+ plasma levels Bupivacaine Potentiation of both types of NM blockers Lidocaine、Procaine Potentiation of SCh block

Nicotinic antagonists Clinical Considerations of Neuromuscular Blockers Histamine release (Tubocurarine) Cardiovascular system Arrhythmia Non-selective block at muscarinic receptor Tachycardia Gallamine Patients with renal impairment Neonatal SCh is less potent Atracurium & dTC are more potent

AntiCholinesterase Cholinesterase AntiCholinesterase (AntiChE) Acetylcholinesterase Cholinergic synapses Butyrylcholinesterase Pseudocholinesterase、Plasma AntiCholinesterase (AntiChE) Reversible Carbamates Irreversible Organophosphates Insecticides、Nerve gases

Approximate duration of action AntiCholinesterase Therapeutic uses & durations of action of AntiChE Uses Approximate duration of action Alcohol Edrophonium Myasthenia gravis、Ileus Arrhythmias 5~15 minutes Carbamates & related agents Neostigmine 0.5~2 hours Pyridostigmine Myasthenia gravis 3~6 hours Physostigmine Glaucoma Ambenonium 4~8 hours Demecarium 4~6 hours Organophosphate Echothiophate 100 hours

AntiCholinesterase Action sites Autonomic ganglion Central nervous system Exocrine Eyes Heart Gastrointestinal tract Neuromuscular junction Respiratory tract

AntiCholinesterase Therapeutic uses of AntiChE Ophthalmology Open angle glaucoma (Echothiophate) Accommodative esotropia (Physostigmine) Predisposing cataract after long term use Neurology Myasthenia gravis treatment (Pyridostigmine、Neostigmine) Diagnose Eaton-Lambert syndrome (Edrophonium) Autoantibody against Ca2+ channels (Presynaptic) Muscle weakness by NM blocker but not by depolarizing

AntiCholinesterase Therapeutic uses of AntiChE Cardiology AV nodal reentrant tachycardia (Edrophonium) Abdominal distention (Neostigmine) Intoxication of atropine (Physostigmine)

AntiCholinesterase Clinical Considerations of AntiChE Alzheimer’s Disease-mild to moderate Tacrine：Hepatotoxicity Donepezil、Rivastigmine、Galantamine Contraindication Cardiac disease、Peptic ulcer、Epilepsy Side Effects GI disturbance Nausea、Vomiting、Anorexia、Diarrhea Abdominal cramping Tremor Anxiety、Depression

AntiCholinesterase Organophosphate Intoxication Acute toxicity：Respiratory failure Respiratory muscle paralysis Tetanic fade of skeletal muscle Nicotinic Ach receptor activation Respiratory center inhibition Muscarinic Ach receptor activation Bronchoconstriction Bronchial smooth muscle contraction Bronchosecretion overactive Exocrine secretion

AntiCholinesterase Treatments for organophosphate acute toxicity Atropine Anti-muscarinic actions, peripherally & centrally Oximes：Pralidoxime (PAM) or Obidoxime Reactivators of AChE but not aged AChE Aged AChE：De-alkylation of AChE-P Diazepam Anti-convulsion Partially reverse muscle paralysis Microsomal enzyme inhibitors Preventing parathion being converted to toxic paraxon

AntiCholinesterase Nerve gases The most toxic substances in the word Diisopropyl fluorophosphate (DFP) Tabun (GA)、Sarin(GB)、Soman、VX Easily aging of phosphorylated cholinesterase Prevention Carbamates (Pyridostigmine) Cholinesterase Fetal calf serum AChE Human butyl cholinesterase Antibody

Cholinergic Agonists Therapeutic Uses ↑ GI motility Post-operation Post-partum For Urinary retention ↑ Salivation For xerostomia in Sjogren’s syndrome Open-angle glaucoma Miosis for cataract surgery

Cholinergic Agonists

Cholinergic Agonists Methacholine Carbachol Bethanechol Asthma diagnosis Carbachol Glaucoma Miotic Bethanechol ↑ GI motility Urinary retention Cevimeline (M3 selective) Xerostomia in Sjogren’s syndrome

Cholinergic Agonists Clinical Considerations Side Effects Asthma attacks ↓ Blood pressure Flushing、Cramps Diarrhea、 Nausea、 Sweating Contraindications Urinary tract obstruction Peptic ulcer Intestinal resection or anastomosis