Nursing Pharmacology Chapter 5:  Autonomic Pharmacology: Cholinergic Drugs

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• Location of cholinergic synapses mainly determine the spectrum of action of acetycholine and choline esters.

• Cholinergic synaptic sites are located:

  • At autonomic effector sites that are innervated by post-ganglionic parasympathetic fibers.

  • At some central nervous system (CNS) synapses.

  • At autonomic ganglia and at the adrenal medulla.

  • At skeletal muscle motor endplates (motor nerves).

• Systemic administration of acetylcholine (ACh) may theoretically act at these sites, but poor CNS penetration and plasma butyrylcholinesterase which hydrolysizes ACh limit systemic effects.

  • ACh is a charged, quaternary nitrogen compound; charged molecules transfer with difficulty across biological membranes.

• Acetylcholine (and other choline esters) effects are initiated by interaction with cholinergic receptors, designated either as muscarinic or nicotinic types.

  • Muscarinic receptors (so defined based of their response to the agent muscarine) are found not only at post-ganglionic parasympathetic effector sites but also at autonomic ganglion cells and adrenal medulla where they modulate nicotinic receptor-mediated effects.

  • Nicotinic receptors are the primary cholinergic receptors at autonomic ganglia and skeletal muscle neuromuscular junctions.

    • These receptors were named because of their responsiveness to the alkaloid nicotine.

• Cholinergic influences are prominent in many organ systems:

1. Modified from Table 7-1: Brown, J.H. and Taylor, P. Muscarinic Receptor Agonists and Antagonists, In, Goodman and Gillman's The Pharmacological Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, p 143

2. Brown, J.H. and Taylor, P. Muscarinic Receptor Agonists and Antagonists, In, Goodman and Gillman's The Pharmacological Basis of Therapeutics,c(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) TheMcGraw-Hill Companies, Inc.,1996, p 142-143.