Pharmacology of the Autonomic Nervous System
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The document discusses the autonomic nervous system and pharmacology of its sympathetic and parasympathetic divisions. It describes the pre- and post-ganglionic fibers, neurotransmitters, and receptors involved. Catecholamines, adrenergic receptors, and drugs that target the sympathetic system like agonists, antagonists, and their effects are summarized. Parasympathetic muscarinic and nicotinic receptors, cholinergic drugs like direct and indirect agonists, and anticholinergic drugs are also outlined.
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Pharmacology of the Autonomic Nervous System
- 1. Introduction to Pharmacology February 2015 Diogo José Capela Oliveira João Daniel Soares Almeida AUTONOMIC NERVOUS SYSTEM Pharmacology of the
- 2. Functions of the autonomic nervous system: - Maintaining homeostasis of the organism - Coordinate the body’s response to exercise, stress or injury
- 3. Sympathetic Nervous System Parasympathetic Nervous System PRE-GANGLIONIC FIBER SHORT LONG POST-GANGLIONIC FIBER LONG SHORT
- 4. Sympathetic Nervous System Parasympathetic Nervous System Pre-ganglionic Neuron ● Acetylcholine ● Acetylcholine Post-ganglionic Neuron ● Nicotinic Receptors ● Nicotinic Receptors ● Norepinephrine ● Acetylcholine ● Acetylcholine ● Dopamine Tissue Receptor ● Adrenergic Receptors ● Muscarinic Receptors ● Muscarinic Receptors ● Dopamine Receptors Exceptions of the Sympathetic Nervous System Adrenal Medulla Releases norepinephrine Sweat Glands Releases acetylcholine Renal Vasculature Releases dopamine
- 5. Catecholamines Receptors: - α1 Receptors - α2 Receptors - β1 Receptors - β2 Receptors - Dopamine Receptors Catecholamines: - Epinephrine - Norepinephrine - Dopamine DRUG AGONIST ANTAGONIST
- 6. ADRENERGIC AGONIST ADRENERGIC RECEPTOR ADRENERGIC RECEPTOR ADRENERGIC ANTAGONIST Stimulates a response through catecholamines. Inhibits the action of catecholamines.
- 7. Most drugs interact with more than one receptor type! But usually they have more affinity to one specific type of receptor.
- 8. α1 Agonists Some of the important effects of α1 agonists: - Mydriasis - Raising blood pressure - Piloerection - Contraction of bladder sphincters - Contraction of the spleen capsule
- 9. α1 Agonists Phenylephrine - Treat hypotensive states - Mainly stimulates α1 receptors Norepinephrine - Treatment of shock - Great capacity in stimulating both α1 and β1 receptors Epinephrine - Support blood pressure during anaphylaxis These agents are sometimes used with local anesthetics
- 10. α1 Antagonists Some of the important effects of α1 antagonists: - Negates de responses of the α1 receptor - Reduces the blood pressure Some of the α1 antagonist agents: - Phentolamine - Phenoxybenzamine - Prazosin
- 11. α1 Antagonists Phentolamine - Competitive, short-acting - Help diagnose pheochromocytoma - Side effects: - Cardiac stimulation - Abdominal cramping (chronic use) - Ulcer exacerbation (chronic use) - Diarrhea (chronic use) Phenoxybenzamine - Non-competitive, long-acting - Managment of pheochromocytoma Prazosin - Treatment of hypertention - Treatment of congestive heart failure - Side effects: - “Prazosin syncope”
- 12. α2 Agonists Some of the uses of α2 agonists: - Antihypertensive - Sedative - Treatment of opiate dependence - Treatment of alcohol withdrawal symptoms Clonidine is used as a treatment for: - High blood pressure - Attention-deficits / Hyperactivity - Anxiety disorders - Migraine - Menopausal flushing - Diarrhea - Side effects: - Hypotension - Dry mouth
- 13. α2 Antagonists Yohimbine: - Treatment of erectile dysfunction - Aphrodisiac effects - Treatment of dry mouth - Treatment of sexual dysfunction
- 14. β Agonists Isoproterenol - Stimulates both β1 and β2 receptors - Bronchioles are relaxed (β2) - Gravid uterus is relaxed (β2) - Increased contractiity and heart rate (β1) Dobutamine - Stimulates selectively β1 receptors - Increased contractiity and heart rate
- 15. β Antagonists Propranolol - Inhibits both β1 and β2 receptors - Reduces heart rate, contractility and blood pressure - Increases bronchiolar tone - Side effects: - Hearth failure - Reduced AV conduction - Worsened COPD Metoprolol - Inhibits selectively β1 receptors
- 16. Acetylcholine Receptors • Acetylcholine Postganglionic neurotransmitter in the PNS Preganglionic neurostranmitter for both SNS and PNS • Cholinergic receptor Muscarinic receptor (M) Nicotinic receptor (N)
- 17. Muscarinic receptors location • Tissues innervated by postganglionic parasympathetic neurons • Presynaptic noradrenergic and cholinergic nerve terminals • Non-innervated sites in vascular endothelium • Central nervous system
- 18. Muscarinic receptors subtypes • There are 5 subtypes of muscarinic receptors: M1, M2, M3, M4, and M5 • They mediate their effects through: • G proteins coupled to - • Phospholipase C (M1,3,5), • Potassium channels (M2,4)
- 19. Nicotinic receptor location • Sympathetic and parasympathetic ganglia • Adrenal medulla • Neuromuscular junction of the skeletal muscle • Central nervous system
- 20. Nicotinic receptor subtypes • There are two subtypes of nicotinic receptors NM and NN Nicotinic receptor Action NM Mediates skelital muscle stimutalion NN Mediates stimulation of the ganglia of the ANS
- 22. Direct-acting muscarinic agonists The direct-acting agents include: • Achetylcoline and choline derivates (longer duration and more selective) • Pilocarpine
- 23. Autonomic effects of muscarinic agonists Local of action Effect Iris sphincter muscle Miosis Ciliary muscle Contraction Sinoatrial node Bradycardia Atrioventricular node Reduced conduction velocity Atrium Reduced contractility Bronchial muscle Contraction Gastrointestional tract Increased motility and secretion Bladder (detrusor) Contraction Bladder (trigone, sphincter) Relaxation Salivary and lacrimal glands Secretion Sweat glands Secretion
- 24. Nicotinic Agonists • Nicotin is the most commonly encountered nicotinic agonist • Stimulates both symphatetic and parasympathetic ANS. • 1 mg: blood pressure by 10 mmHg and heart rate 15bpm peripheral vascular resistance, cardiac output, heart work High doses: Bradycardia, hypotension, nausea tremors and convulsions
- 25. Direct acting cholinergic drugs Bethanechol is used in: • Urinaty retention ( not obstructed ) • Xerostomia ( Sjogren’s syndrome, traumatic or radiation injury ) • Gastroparesis • Impaired gastric absorption Side effects: • Hypotension and bradycardia • Myocardial ischemia ( high doses )
- 26. Direct acting cholinergic drugs Pilocarpine used in: • Xerostomia ( more commonly than bethanechol) • Open-angle glaucoma. Side effects: • Sweating • Asthma worsening • Nausea • Hypotension • Bradycardia • Hiccups
- 27. Indirect-acting cholinergic drugs “Cholinesterase inhibitors”
- 28. Reversible cholinosterase inhibitors Inhibitor Duration Main site of action Clinical use Adverse effects Edrophonium Short (10m) Neuromuscular juntion Diagnosis of myasthenia gravis Cramps Physostigmine Medium (0,5-5h) Postganglionic parasympathetic Glaucoma (eye drops) Anticholinergic syndrome Nausea, sweating, bradycardia Neostigmine Medium (1-2h) Neuromuscular juntion Nonobstructive paralytic ileus. Myasthenia gravis (orally)
- 29. Irreversible cholinesterase inhibitors • Long acting • Organophosphates • Insecticides • War gases Include: • Parathion • Malathion • Sarin
- 30. Irreversible cholinesterase inhibitors intoxication Muscarinic Nicotinic CNS Salivation Fasciculations Anxiety Lacrimation Weakness Confusion Urination Adrenomedullary discharge Tremors Defecation Gastrointertinal spasms Emesis (vomiting) Miosis Bradycardia Hypotension Dyspnea Therapy: Pralidoxime + Atropine (Anticholinergic drugs)
- 32. Muscarinic Antagonists ( Atropa belladonna) Classicly derived from plantsLocal of action Effect Iris sphincter muscle Mydriasis Ciliary muscle Cycloplegia Sinoatrial node Thachycardia Exocrin glands Decreased secretions Bladder Urinary retention Salivary and lacrimal glands Xerostomia and decreased lacrimation Sweat glands Hypohidrosis Ex: Atropine (non-selective muscarinic antagonist) Pirenzipine (M1 selective muscarinic antagonist)
- 33. Nicotinic Antagonists – Neuromuscular blockers Neuromuscular blockers Nondepolarizing agents Tubocurarine Depolarizing agents Succinylcholine
- 34. THE END