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Curare

Curare is a potent neurotoxin[?]. It is a natural resinous extract obtained from several tropical American woody plants, especially Chondrodendron tomentosum[?] or certain South American species of Strychnos[?], used as an arrow poison by some Indian peoples of South America. The name is derived from similar-sounding Indian names for the concoction. The plants themselves are sometimes called curare.

The Indian peoples prepared it by combining young-bark scrapings of the relevant plants with other cleaned plant fragments and sometimes snake venom or venomous ants. This mixture was boiled in water for about two days and then strained and evaporated to become a dark, sticky, bitter-tasting paste. The potency would be tested by counting the number of steps a small animal would take after being pricked. Darts were tipped with curare and then fired through blowguns made of bamboo. Death for birds would take one to two minutes, small mammals up to ten minutes, and large mammals (e.g. tapirs) about 20 minutes. Curare, a major industry for some tribes, was generally too expensive and scarce to be used in warfare.

The principal chemicals of curare are alkaloids that affect neuromuscular transmission. Among the many alkaloids present in curare preparations, the most important ones are curarine[?] and tubocurarine[?].

Death from curare is caused by asphyxia, because the skeletal muscles[?] become relaxed and then paralyzed. Research has shown that curare causes a weakening or paralysis of skeletal muscles by interfering with the transmission of nervous impulses between the nerve axon and the contraction mechanism of the muscle cell. Specifically, the alkaloid interferes with the activity of acetylcholine (depolarizing the cell end-plate) at the surface where it functions, thereby blocking the neuromuscular junction. The poison only works in the blood; poisoned animals have no harmful effects on humans if ingested. Its vapors are not poisonous, although many tribes believed they were.

Curiously, during curare poisoning the victim is very much awake and aware of what is happening until the loss of consciousness. Consequently, the victim can feel the progressive paralysis but cannot do anything to call out or gesture. If artificial respiration is performed throughout the victim will recover and have no ill effects.

Curare, usually in the form of d-tubocurare, was the first muscle relaxant to be used medically. Nowadays, synthetic drugs such as Pancuronium bromide with similar molecular action are used. Especially in abdominal surgery, the muscle-relaxant effect of many anaesthetics in usual doses is not potent enough to facilitate operative procedures such as wound closure and suturing. Therefore, curare-like drugs are combined with relatively low doses of anaesthetics. The first recorded application of curare in this role was by a German surgeon, Arthur Lwen, in 1912, but it became commonplace only after trials by Dr Harold Griffith and Enid Johnson of Montreal, Canada in 1942.

It is also useful for treating the paralysis caused by tetanus because the muscle relaxant counters the contractions caused by the tetanus toxin; and as a relaxant during the setting of broken bones.



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