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AUTONOMIC SYSTEMS AND DRUGS-2 Neurotransmitters Epinephrine Norepinephrine Acetyl choline Adrenergic Cholinergic Innervation HR Contractility Transmitter(s) Sympathetic Norepinephrine Epinephrine Parasympathetic Acetyl Choline Important Exception Vascular smooth muscle Sympathetic only (or nearly so) Catecholamine Biosynthesis Synthesized from: Tyrosine Rate limiting reaction: Tyrosine hydroxylase Catecholamine Degradation COMT - catechol-O-methyltransferase MAO - monoamine oxidase Norepinephrine Inactivation Reuptake into the nerve ending by an active transport system Drugs Acting Presynaptically Reserpine Inhibits storage in vesicles -Methyldopa False transmitter Guanethidine Inhibits NE release Amphetamine Stimulates NE release Imipramine Inhibits NE reuptake Fluoxetine Inhibits serotonin reuptake Postsynaptic Receptors (Adrenergic) Alpha Beta Generally excitatory Generally inhibitory Exception: intestinal smooth muscle Exception: beta1 in the heart Postsynaptic Receptors (Cholinergic) Muscarinic Nicotinic Acetyl Choline Inactivation Acetylcholinesterase Cholinergics Cholinergic agonists •Bethanechol •Pilocarpine •Carbachol Antimuscarinics •Atropine •Scopolamine Anticholinesterases •Neostigmine •Organophosphates (e.g. DFP) Neuromuscular blockers •Tubocurarine •Pancuronium •Succinyl Choline Cholinergic Agonists Parasympathomimetics: limited uses •Glaucoma •Pupillary constriction (meiosis) Not used for: •Bronchial Asthma •Coronary Insufficiency •Peptic Ulcer •Hyperthyroidism Antimuscarinics Atropine; Scopalamine Therapeutic uses: •Motion sickness •Pupillary dilation •Parkinson’s Disease Side effects: •Dry mouth •Blurred vision •Tachycardia •Urinary retention •Constipation Anticholinesterases Reversible Irreversible Neostigmine Physostigmine Organophosphates (e.g. DFP) Predict effects on: • Eye • GI tract • Urinary tract • Skeletal muscle Reversal of organophosphate poisoning: • Atropine • Pralodoxime Reversal of atropine poisoning: • Physostigmine Therapeutic Uses of Anticholinesterases • Glaucoma • Paralytic ileus • Mysathenia gravis Pancuronium Succinylcholine Mechanism Competitive Depolarizing Onset 1-2 min 20-40 sec Duration 30-60 min 2-5 min Side Effects BP tendency Cardiac arrhythmia Prolonged apnea Malignant hyperthermia Adrenergics Autonomic reflexes modulate drug responses BP SNS PSNS BP SNS PSNS What is the treatment of choice for anaphylactic shock? Epinephrine Why? It is the only drug that addresses the most serious manifestations: • b1 increases cardiac output • b2 relaxes constricted bronchioles • 1 constricts capillaries b2-Selective Adrenergic Agonists • Albuterol • Terbutaline Bronchial dilators Uterine relaxant (ritodrine) 1 Adrenergic Agonists •Phenylephrine •Ephedrine Therapeutic uses: •Nasal decongestants •Used with local anesthetics •Local hemostasis •Mydriatic •Glaucoma •Vasopressor •Appetite suppressant Adrenergic Antagonists Alpha blockers • Prazosin (1) • Phenoxybenzamine (12) • Phentolamine (12) Hypertension Adrenergic Antagonists Beta blockers: •Propranolol (b1 b2) •Metoprolol (b1 ) •Atenolol (b1 ) •Timolol (b1 b2) Therapeutic uses: •Arrhythmia •Angina pectoris •Hypertension Adverse Effects Alpha blockers • Postural hypotension • Tachycardia • First dose (prazosin) Beta blockers • Cardiac depression • Asthma attack • Nightmares, lassitude, depression • Angina pectoris (abrupt withdrawal) Anti-Parkinson’s Drugs Tolcapone Carbidopa Selegiline Adverse Effects Reduced with carbidop a GI - nausea and vomiting Hypotension Dyskinesias Psychiatric reactions Drugs to Know Levodopa used in combination Carbidopa Amantidine DA reuptake inhibitor (?) Bromocryptine DA receptor agonist Selegiline MAO-B inhibitor Tolcapone COMT inhibitor
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