Chemical Terrorism

By James A. Geiling, MD, FCCP

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Nerve Agents

Background

Nerve agents are normally liquids, with "G" agents being more volatile than "V" agents; sarin (GB) is the most volatile. They can be dispersed from missiles, rockets, bombs, artillery shells, spray tanks, land mines, canisters, or other munitions.

Nerve agents act as organophosphorous cholinesterase inhibitors, inhibiting plasma butyrylcholinesterase, RBC acetylcholinesterase, and acetylcholinesterase at tissue cholinergic receptor sites. After an acute exposure, the RBC enzyme activity best reflects enzyme activity in tissue, whereas the plasma enzyme activity more accurately reflects tissue activity during recovery. Nerve agents bind to acetylcholinesterase (AChE) and prevent hydrolysis of acetylcholine (ACh). The clinical effects, therefore, occur from an excess of ACh. Attachment of the agents to AChE is permanent, its activity returning only with new enzyme synthesis or RBC turnover (1%/d).⁶

Excess ACh affects both muscarinic and nicotinic sites. Muscarinic sites that become involved include postganglionic parasympathetic fibers, glands, pulmonary and GI smooth muscles, and organs targeted by CNS efferent nerves, such as the heart via the vagus nerve. Nicotinic sites include autonomic ganglia and skeletal muscle.

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