Pharmacology of Parasympathetic System, Histamine, Serotonin & Related Drugs

A comprehensive set of vocabulary flashcards covering parasympathetic pharmacology, cholinergic and anticholinergic drugs, histamine and serotonin pharmacology, gastrointestinal therapeutics, laxatives, and NSAID mechanisms and agents.

Acetylcholine (ACh)

Endogenous cholinergic neurotransmitter that activates muscarinic and nicotinic receptors.

Choline Acetyltransferase (ChAT)

Enzyme that synthesizes ACh from choline and acetyl-CoA inside cholinergic neurons.

Acetylcholinesterase (AChE)

Synaptic enzyme that rapidly hydrolyzes ACh into choline and acetate.

Hemicholinium

Drug that blocks high-affinity uptake of choline into the presynaptic terminal, inhibiting ACh synthesis.

Vesamicol

Inhibits vesicular ACh transporter (VAT) and prevents ACh storage in synaptic vesicles.

Botulinum toxin

Pre-synaptic blocker that cleaves SNARE proteins and prevents ACh release.

Muscarinic Receptor M1

Gq-coupled receptor; mediates CNS excitation and stimulates enteric nervous system.

Muscarinic Receptor M2

Gi-coupled receptor in heart; decreases heart rate and atrial contractility.

Muscarinic Receptor M3

Gq-coupled receptor on glands and smooth muscle; increases secretions, bronchoconstriction, miosis, etc.

Nicotinic Receptor (NN)

Ligand-gated Na⁺/K⁺ channel in autonomic ganglia and adrenal medulla.

Nicotinic Receptor (NM)

Ligand-gated Na⁺/K⁺ channel at skeletal neuromuscular junctions.

Parasympathomimetic (Cholinomimetic)

Agent that mimics or enhances the effects of ACh on the parasympathetic nervous system.

Parasympatholytic

Drug that antagonizes or blocks parasympathetic (muscarinic) activity.

DUMB BELSS

Mnemonic for cholinergic toxicity: Diarrhea, Urination, Miosis, Bronchospasm, Bradycardia, Emesis, Lacrimation, Sweating, Salivation.

Bethanechol

Direct-acting muscarinic agonist used for postoperative urinary retention and atonic bowel.

Carbachol

Direct muscarinic/nicotinic agonist; applied topically for glaucoma, causes miosis.

Methacholine

M3-selective agonist employed in bronchial challenge testing for asthma diagnosis.

Pilocarpine

Alkaloid muscarinic agonist for glaucoma and xerostomia; penetrates CNS.

Cevimeline

M3-preferring agonist used to increase salivation in Sjögren syndrome.

Edrophonium

Short-acting reversible AChE inhibitor; used to diagnose myasthenia gravis (Tensilon test).

Neostigmine

Carbamate AChE inhibitor; treats myasthenia gravis and reverses non-depolarizing NM blockade.

Physostigmine

Carbamate AChE inhibitor that crosses BBB; antidote for antimuscarinic toxicity.

Pyridostigmine

Longer-acting carbamate AChE inhibitor; maintenance therapy for myasthenia gravis.

Rivastigmine

AChE inhibitor used for Alzheimer’s disease; available as transdermal patch.

Donepezil

Centrally acting AChE inhibitor for Alzheimer’s dementia; often combined with memantine.

Galantamine

Reversible AChE inhibitor for mild to moderate Alzheimer’s disease.

Tacrine

First AChE inhibitor for Alzheimer’s; limited by hepatotoxicity.

Organophosphate

Irreversible AChE inhibitor class (e.g., malathion, sarin) causing cholinergic crisis.

Pralidoxime (2-PAM)

Oxime that reactivates phosphorylated AChE; antidote for early organophosphate poisoning.

Atropine

Non-selective muscarinic antagonist; treats bradycardia and organophosphate poisoning.

Scopolamine

Muscarinic antagonist with CNS action; prevents motion sickness (transdermal patch).

Ipratropium

Inhaled muscarinic antagonist (M3) for acute asthma and COPD; quaternary amine.

Tiotropium

Long-acting inhaled M3 antagonist for maintenance therapy in COPD.

Glycopyrrolate

Peripheral muscarinic blocker that reduces secretions and treats peptic ulcer; does not cross BBB.

Oxybutynin

M3-selective antagonist that decreases detrusor tone; used for urge incontinence.

Benztropine

Central muscarinic antagonist used to treat Parkinsonian tremor and drug-induced extrapyramidal effects.

Hexamethonium

Prototype ganglionic nicotinic blocker; historically used for hypertension.

Succinylcholine

Depolarizing neuromuscular blocker; fast onset, short duration for intubation.

d-Tubocurarine

Prototype non-depolarizing neuromuscular blocker; causes histamine release and hypotension.

Pancuronium

Long-acting non-depolarizing NM blocker; vagolytic properties increase heart rate.

Rocuronium

Intermediate-acting non-depolarizing NM blocker with rapid onset; used for rapid sequence intubation.

Histamine

Biogenic amine formed from histidine; mediates allergic reactions, gastric acid secretion, and neurotransmission.

H1 Receptor

Gq-coupled histamine receptor producing vasodilation, bronchoconstriction, pain, and itching.

H2 Receptor

Gs-coupled histamine receptor on gastric parietal cells; stimulates hydrochloric acid secretion.

Triple Response of Lewis

Intradermal histamine reaction: red spot, wheal (edema), and flare due to H1 activation.

First-Generation H1 Antihistamine

Lipophilic H1 blockers (e.g., diphenhydramine) that penetrate BBB and cause sedation & anticholinergic effects.

Second-Generation H1 Antihistamine

Peripherally selective H1 blockers (e.g., cetirizine) with minimal CNS sedation.

Diphenhydramine

Ethanolamine first-generation H1 blocker used for allergy, insomnia, and motion sickness.

Promethazine

Phenothiazine antihistamine with strong anti-emetic and α-blocking properties.

Cetirizine

Second-generation piperazine H1 blocker; non-sedating antihistamine.

Loratadine

Long-acting second-generation piperidine antihistamine; minimal CNS effects.

Fexofenadine

Active metabolite of terfenadine; non-sedating second-generation H1 blocker.

Cimetidine

Prototype H2 blocker; least potent, inhibits CYP enzymes and may cause gynecomastia.

Ranitidine

H2 antagonist used for peptic ulcer and GERD; fewer endocrine effects than cimetidine.

Famotidine

Most potent H2 blocker; minimal drug interactions.

Serotonin (5-Hydroxytryptamine, 5-HT)

Monoamine transmitter synthesized from tryptophan; regulates mood, vasoconstriction, and GI motility.

5-HT1A Receptor

Presynaptic CNS receptor; activation decreases serotonin release.

Buspirone

Partial 5-HT1A agonist used as non-sedating anxiolytic.

5-HT1B/1D Receptors

Vascular receptors mediating cranial vasoconstriction; therapeutic targets in migraine.

Triptans

Selective 5-HT1B/1D agonists (e.g., sumatriptan) that abort acute migraine attacks.

5-HT2A Receptor

Receptor on smooth muscle causing contraction; target of ergot alkaloids.

Ergotamine

Ergot alkaloid 5-HT2 agonist; vasoselective drug for acute migraine.

5-HT3 Receptor

Ligand-gated cation channel on vagal afferents/CTZ; mediates emesis.

Ondansetron

Selective 5-HT3 antagonist for chemotherapy-induced nausea and vomiting.

5-HT4 Receptor

Gs-coupled receptor in GI tract; stimulates peristalsis.

Cisapride

5-HT4 partial agonist promoting GI motility; limited by cardiac arrhythmia risk.

Proton Pump Inhibitor (PPI)

Irreversible H⁺/K⁺-ATPase inhibitor (e.g., omeprazole) that suppresses gastric acid secretion.

Antacid

Base (e.g., Mg(OH)₂, CaCO₃) that neutralizes gastric acid in peptic ulcer disease.

Sucralfate

Aluminum sucrose sulfate that binds ulcers forming protective barrier.

Misoprostol

Prostaglandin E₁ analog that increases mucus/HCO₃⁻ and prevents NSAID-induced ulcers; abortifacient.

Bismuth Subsalicylate

Coating agent with antimicrobial action; causes black stool and tongue.

Bulk-Forming Laxative

Fiber agents (psyllium) that absorb water, increasing stool bulk and promoting peristalsis.

Psyllium

Plant fiber bulk laxative effective within 12–72 h; may cause bloating if not taken with water.

Stool Softener

Surfactant (docusate) that lowers stool surface tension allowing water penetration.

Osmotic Laxative

Poorly absorbed agents (PEG, lactulose) drawing water into lumen to soften stool.

Polyethylene Glycol (PEG)

Non-absorbable osmotic laxative commonly used for bowel prep.

Stimulant Laxative

Agents (senna, bisacodyl) that directly stimulate enteric nerves to increase motility.

Cyclooxygenase (COX)

Enzyme converting arachidonic acid to prostaglandins; exists as constitutive COX-1 and inducible COX-2.

Prostaglandin I₂ (PGI₂)

Vascular prostacyclin causing vasodilation and inhibiting platelet aggregation.

Thromboxane A₂ (TXA₂)

Platelet eicosanoid that induces vasoconstriction and promotes aggregation.

Leukotrienes

Lipooxygenase metabolites (LTC₄, LTD₄) that mediate bronchoconstriction and anaphylaxis.

Aspirin

Irreversible COX-1/2 inhibitor; low dose antiplatelet, high dose anti-inflammatory; risk of Reye syndrome.

Ibuprofen

Propionic acid non-selective NSAID used for pain and inflammation.

Indomethacin

Potent indole NSAID; closes PDA and treats acute gout but has high GI/CNS toxicity.

Diclofenac

Phenylacetic acid NSAID with potent COX inhibition; topical preparations available.

Piroxicam

Enolic acid NSAID with long half-life; high risk of peptic ulcer and bleeding.

Celecoxib

Selective COX-2 inhibitor; spares gastric mucosa but increases thrombotic risk.

Dicyclomine

M3 antagonist used as antispasmodic for irritable bowel syndrome.

Zileuton

5-Lipoxygenase inhibitor that decreases leukotriene synthesis; used in asthma control.

Zafirlukast

Leukotriene receptor (CysLT1) antagonist for prophylactic asthma therapy.