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Glossary


organophosphate (OP)


The term is generally undestood to mean an organic derivative of phosphoric or similar acids. Many OPs inhibit an enzyme known as acetylcholinesterase, but not all OPs (e.g. glyphosate) demonstrate this effect. Some OPs react with other proteins such as neuropathy target esterase. Inhibitors of acetylcholinesterase affect certain nerve junctions in animals, as well as parasympathetic effector sites (the heart, lungs, stomach, intestines, urinary bladder, prostate, eyes and salivary glands). The transmission of impulses across nerve junctions involves the release of a transmitter chemical, which, in the case of many nerves, is acetylcholine. To stop the nerve continuing to transmit the message, the transmitter, acetylcholine, must be broken down immediately after it has had its effect. This breakdown is brought about by an enzyme, acetylcholinesterase. By inhibiting the enzyme acetylcholinesterase, OPs prevent the nerve junction from functioning properly. In humans, anticholinesterase OPs have broadly similar actions to those seen in other species. Acetylcholinesterase inhibition causes acute effects in humans and other mammals. The symptoms in humans, which generally occur when acetylcholinesterase activity has been reduced by about 50%, may include: headache, exhaustion and mental confusion together with blurred vision, sweating, salivation, chest tightness, muscle twitching and abdominal cramps. The severity of the effects depends on the degree of acetylcholinesterase inhibition.


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