Cholinergic system and drugs

• Acetylcholine (Ach) is a neurotransmitter.
• It has got 2 receptors-muscuranic and nicotinic receptors
• Muscuranic receptors are of three types-M1,M2,M3
• Nicotinic receptor is of two types Nm & Nn
• M2,M3 receptors are of more significance and would be discussed in this article.
• M2 receptors are present on heart and they cause bradycardia,marked decrease in force of contraction and rate of conduction.
• M3 receptors are present on glands and regulate there secretion.They are also present on vessels and causes vasodilatation by releasing EDRF.
• Actions-

1. Ach causes bradycardia,slow conduction and reduced contraction
2. Ach causes vasodilatation.Although they supply only vessels of face and neck,so flushing is seen on face.
3. Ach causes constriction of smooth muscles.They are potent broncho constrictor  
4. Ach increases secretion from all glands like salivary,lacrimal,sweat glands

• Cholinesterase is the enzyme that causes lysis of Ach.Anticholinesterase drugs mimic the action of Ach.
• Some anticholinesterase drugs are - Physostigmine;Neostigmine