Bodily Defenses Image Map

Cholinesterase Inhibitors

Can you imagine a family of chemicals that have been used for everything from pesticides to medicines to biochemical weapons of war? Well, there is such a group of compounds. They are called cholinesterase inhibitors. The name says what they do: they inhibit an enzyme called cholinesterase.

Remember in "What We Know" when we talked about how nerve cells communicate with each other and with muscle by releasing chemical messengers (neurotransmitters)? One of the more common neurotransmitters is acetylcholine.  Acetylcholine is the transmitter at all junctions of nerves and skeletal and heart muscle, intestines, bladder, blood vessels, and glands.

So what do you think would happen if these acetylcholine nerves were continuously active and releasing acetylcholine to their target nerve, gland, and muscle cells?  Would the build up of acetylcholine cause excessive action on their targets? Think about muscle, for example.  Release of acetylcholine causes muscle cells to contract. But if acetylcholine were always there, your muscles would be constantly contracting - you would be in a constant state of convulsion. 

Even animals as primitive as insects have evolved a way to get rid of excess acetylcholine. They have an enzyme (cholinesterase) present in the junctions of acetylcholine neurons that destroys acetylcholine. What would happen if we had a pesticide chemical that inhibited the cholinesterase in insects? With no enzyme to destroy cholinesterase and acetylcholine would pile up in the junctions. In the case of insects, they die because they cannot pump air in and out and because their "heart" stops pumping.

Symptoms of Cholinesterase Inhibitor Poisoning

  • muscle weakness
  • difficulty walking
  • wheezing, coughing
  • difficult breathing
  • blurry vision
  • vomiting
  • sweating
  • seizures, coma

 

Many well-known insecticides are cholinesterase inhibitors (See table). These compounds are used in hand sprayers for home gardens as well as in crop dusting airplanes for large farms.

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So where is the environmental hazard with pesticides? One potential hazard is in careless handling of the pesticide, which is highly concentrated as it is sold in garden and farm stores. Spilling the concentrate on your skin could cause poisoning. Residues on food that is not thoroughly washed before eating can create a hazard. Obviously, little children should be kept away from such chemicals so they don't accidentally get exposed to concentrate.

Common Pesticides that
Inhibit Cholinesterase

malathion
parathion
sevin
diazinon
These compounds contaminate the environment. They are toxic not only to insects but also to fish, birds, and other wildlife. Because insecticides pollute the environment, people are becoming increasingly interested in utilizing nature's own weapons against insects. This has led to the practice called "integrated pest management," an approach to insect and disease control that includes:
  •  the genetic engineering of plants that either resist insects or that give off odors or tastes that repel insects
  • the use of bacteria or viruses that are toxic to insects
  • the use of animals (purple martin birds, wasps, frogs, snakes) that feed on insects

"Integrated Pest Management" uses many approaches for controlling insects

Click here for a history of integrated Pest Management
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