Cholinergic Pharmacology Quiz

History and Effects of Antinicotinic and Antimuscarinic Agents

• Antinicotinic agents like tubocurarine and hexamethonium block acetylcholine action at nicotinic acetylcholine receptors, leading to various adverse effects.
• Antimuscarinic agents, found in Belladonna plants, were used as deadly poison in the Roman Empire and Middle Ages; atropine was used as an antispasmodic in asthma treatment and morphine antidote.
• Curare, derived from Chondrodendron and Strychnos, was used as a poison by South American Indians in the 16th century and was found to block the stimulant action of nicotine.
• Muscarinic receptors are G-protein coupled receptors mainly present in the parasympathetic system and sweat glands, while nicotinic receptors are ligand-gated ion channels present in both parasympathetic and sympathetic ganglions, neuromuscular junctions, and the brain.
• Antimuscarinic agents bind to muscarinic cholinergic receptors postsynaptically without activating them, preventing acetylcholine from binding to the active sites of receptors to elicit their effect.
• Antinicotinic agents are classified into ganglionic blockers and neuromuscular blockers, with ganglionic blockers acting at all autonomic ganglions and neuromuscular blockers acting at the neuromuscular junction.
• Adverse effects of antinicotinic and antimuscarinic agents include cognitive function decline, paralysis, tachycardia, hypotension, constipation, dry mouth, dry eyes, hypohidrosis/anhidrosis, blurry vision, increased intraocular pressure, and an increased risk of glaucoma.
• Anticholinergic overdose, both antinicotinic and antimuscarinic, can exert toxic effects on both central and peripheral systems.
• Reid Hunt discovered the fall in blood pressure in rabbits after removing adrenaline from adrenal glands extract, later attributing this effect to acetylcholine, which was 100,000 times more potent in lowering blood pressure.
• Sir Henry Hallett Dale observed acetylcholine causing blood vessel dilation and slowing down heart rate, and in 1914, he named substances that mimic acetylcholine action as “cholinergics”.
• Atropine was first discovered in 1809 and later used as an antispasmodic in asthma treatment and as a morphine antidote, while curare and tubocurarine had important roles in establishing the concept of specific cholinoceptors in the motor end plate.
• Antinicotinic and antimuscarinic agents have various adverse effects, interactions, and contraindications, requiring caution and medical professional advice before usage.