Question

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The use of chemical weapons in times of war is banned by all modern nations that are not ruled by dictatorial governments. A certain class of chemical agents that could be used as weapons, the organo-phosphorus agents (Sarin gas, VX gas, and others), have characteristic mechanisms of action (toxicodynamics), and are especially deadly. Exposure to even a small amount of these agents causes characteristic signs and symptoms, whose severity occurs in a dose-dependent fashion (the more of the agent you are exposed to, the more severe the signs and symptoms). VX gas is so deadly, that the dose required to kill 50% of a population (LD₅₀) is equivalent to only 10 mg of the compound contacting the skin.

Exposure to VX gas produces characteristic initial signs and symptoms include: miosis (pupillary constriction), rhinorrhea (runny nose), bronchoconstriction (constriction of the airways), increased gastric motility with loss of bowel control (uncontrolled defecation), loss of bladder control (uncontrolled urination), sweating, uncontrollable drooling, initial skeletal muscle twitching followed by muscle tetany, and bradycardia (decreased heart rate). Loss of consciousness and seizures quickly follow the onset of these initial signs and symptoms until death by asphyxiation occurs due to the diaphragm becoming paralyzed.     

Even with such a wide variety of neuro-muscular and endocrine signs and symptoms, organo-phosphorus compounds such as VX gas have a single molecular target in the body. Consider your knowledge of the central and peripheral (autonomic and somatic) nervous systems (what they have in common; how they are designed, etc…)

A). Identify the single molecular target of VX gas and other organo-phosphorus agents and indicate the effect that VX gas has on this target; and

C). Are the signs and symptoms described above consistent with activation or inhibition of the sympathetic branch of the autonomic nervous system; activation or inhibition of the parasympathetic branch of the autonomic nervous system; and/or activation or inhibition of the somatic motor nervous system?

B). Rationalize all of the signs and symptoms of VX gas exposure given the physiology and effect of VX on the molecular target you identified in part A above.

Answer 1

Answer A)

VX’s lethal effects take place at the level of the cell by acting on a neurotransmitter called acetylcholine. Neurons normally rely on acetylcholine to send signals to muscles ordering them to move, and once those signals have been sent, acetylcholine breaks down, ending that line of communication. What VX does is prevent acetylcholine from breaking down due to inhibitory effect on AChE ie Acetylcholine Esterase enzyme, this lead yo too much ACh in body and oner stimulation of neurons.

Answer B)

Due to large amount of released Ach it causes overstimulation of constrictor pupilary muscles, arector pili muscles and various other muscles leading to the constricton of pupil,sweating, running nose, increase stomach movements.

Answer C)

It cause bradycardia, uncantrolled & increased muscle contractions, due to activation parasympathetic system.

But increased concentration cause activation of sympathetic nervous systen failure of neuromuscular junction due to overstimulation leading to failure of muscles and paralysis.

Due to large amount of ACh in CNS the brain release large amount of excitatory amino acids which lead to toxicity of brain cells and cause brain death

And in PNS overstimulated mucles can lead to seizures and spasm.