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# Autonomic Pharmacology ### Introduction The autonomic nervous system (ANS) regulates involuntary functions, including heart rate, blood pressure, digestion, and body temperature. It has two main divisions: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). ### Ne...

# Autonomic Pharmacology ### Introduction The autonomic nervous system (ANS) regulates involuntary functions, including heart rate, blood pressure, digestion, and body temperature. It has two main divisions: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). ### Neurotransmitters * **Acetylcholine (ACh)**: Primary neurotransmitter in the PNS and also used in the SNS at sweat glands and some blood vessels. * **Norepinephrine (NE)**: Primary neurotransmitter in the SNS. * **Epinephrine (Epi)**: Released by the adrenal medulla, acts as a hormone. ### Receptors * **Cholinergic Receptors**: Activated by ACh. * Nicotinic (N): Found at neuromuscular junctions, autonomic ganglia, and the adrenal medulla. * Muscarinic (M): Found at effector organs of the PNS, such as the heart, smooth muscle, and glands. * **Adrenergic Receptors**: Activated by NE and Epi. * Alpha ($\alpha$): $\alpha_1$ (vasoconstriction), $\alpha_2$ (inhibition of NE release). * Beta ($\beta$): $\beta_1$ (increased heart rate and contractility), $\beta_2$ (bronchodilation, vasodilation), $\beta_3$ (lipolysis). ### Key Concepts * **Sympathetic Nervous System (SNS)**: * "Fight or flight" response. * Increases heart rate and blood pressure. * Dilates pupils. * Mobilizes energy stores. * **Parasympathetic Nervous System (PNS)**: * "Rest and digest" response. * Decreases heart rate. * Increases digestion. * Constricts pupils. ### Pharmacology #### Cholinergic Drugs * **Agonists (Parasympathomimetics)**: * Direct-acting: Pilocarpine (used for glaucoma). * Indirect-acting (Cholinesterase inhibitors): * Neostigmine (used for myasthenia gravis). * Donepezil (used for Alzheimer's disease). * **Antagonists (Parasympatholytics)**: * Atropine (used to increase heart rate, dilate pupils). * Scopolamine (used for motion sickness). * Ipratropium (used for bronchodilation in COPD). #### Adrenergic Drugs * **Agonists (Sympathomimetics)**: * $\alpha_1$ agonists: Phenylephrine (used as a decongestant). * $\alpha_2$ agonists: Clonidine (used for hypertension). * $\beta_1$ agonists: Dobutamine (used for heart failure). * $\beta_2$ agonists: Albuterol (used for asthma). * Mixed agonists: Epinephrine (used for anaphylaxis). * **Antagonists (Sympatholytics)**: * $\alpha$ blockers: Prazosin (used for hypertension, BPH). * $\beta$ blockers: Propranolol (used for hypertension, anxiety). * Selective $\beta_1$ blockers: Metoprolol (used for hypertension). ### Clinical Applications * **Hypertension**: $\beta$ blockers, $\alpha$ blockers, $\alpha_2$ agonists. * **Asthma**: $\beta_2$ agonists, anticholinergics. * **Glaucoma**: Cholinergic agonists, $\beta$ blockers. * **Heart Failure**: $\beta_1$ agonists (short-term), B blockers (long-term). * **Overactive Bladder**: Anticholinergics. ### Noteworthy | Drug | Receptor Action | Clinical Use | Side Effects | | :------------ | :------------------------------------ | :------------------------------------------- | :----------------------------------------------- | | Atropine | Muscarinic antagonist | Increase heart rate, dilate pupils | Dry mouth, blurred vision, constipation | | Albuterol | $\beta_2$ agonist | Bronchodilation in asthma | Tremors, tachycardia | | Propranolol | $\beta$ blocker | Hypertension, anxiety | Bradycardia, fatigue, bronchospasm | | Pilocarpine | Muscarinic agonist | Glaucoma | Increased salivation, sweating, diarrhea | | Epinephrine | $\alpha$ and $\beta$ agonist | Anaphylaxis | Tachycardia, hypertension, anxiety | | Neostigmine | Cholinesterase inhibitor | Myasthenia gravis | Increased salivation, muscle weakness | | Clonidine | $\alpha_2$ agonist | Hypertension | Sedation, dry mouth | | Metoprolol | Selective $\beta_1$ blocker | Hypertension | Bradycardia, fatigue | | Prazosin | $\alpha_1$ blocker | Hypertension, BPH | Dizziness, orthostatic hypotension | | Ipratropium | Muscarinic antagonist | Bronchodilation in COPD | Dry mouth, blurred vision | | Dobutamine | $\beta_1$ agonist | Heart failure (short-term) | Tachycardia, arrhythmias | | Phenylephrine | $\alpha_1$ agonist | Decongestant | Hypertension, headache | | Scopolamine | Muscarinic antagonist | Motion sickness | Drowsiness, dry mouth, blurred vision | | Donepezil | Cholinesterase inhibitor | Alzheimer's disease | Nausea, vomiting, diarrhea | ### Summary Table of Autonomic Drugs | Drug Class | Mechanism of Action | Primary Use(s) | Common Side Effects | | :----------------------- | :---------------------------------------------------------- | :--------------------------------------------------- | :--------------------------------------------------- | | Cholinergic Agonists | Stimulate muscarinic receptors | Glaucoma, urinary retention, diagnosis of asthma | SLUDGE (Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis) | | Cholinergic Antagonists | Block muscarinic receptors | Motion sickness, COPD, pre-anesthetic | Dry mouth, blurred vision, constipation | | Adrenergic Agonists | Stimulate adrenergic receptors ($\alpha$ and/or $\beta$) | Asthma, hypotension, nasal congestion, anaphylaxis | Hypertension, tachycardia, anxiety | | Adrenergic Antagonists | Block adrenergic receptors ($\alpha$ and/or $\beta$) | Hypertension, BPH, anxiety | Hypotension, bradycardia, fatigue | This table provides a comprehensive overview of autonomic pharmacology, including neurotransmitters, receptors, key concepts, and clinical applications.