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

History

The Native Americans 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.

Toxicology

The active ingredients of curare are alkaloids that affect neuromuscular transmission, thereby acting as muscle relaxants. Among the many alkaloids present in curare preparations, the most important ones are curarine and tubocurarine .

Death from curare is caused by asphyxia resulting from paralysis of the respiratory muscles. The alkaloid curare molecule mimics the neurotransmitter acetylcholine by binding to its receptor at muscle synapses. This prevents nerves from stimulating muscle contraction. The resulting paralysis sets in gradually, because curare must compete for receptor binding sites before occupying them. The toxin kills only if it enters the blood stream. The amounts used to hunt animal are easily broken down in the gut, making the downed game safe for hunters and others to eat. Curare vapor is not poisonous, although many tribes have believed it is.

As curare acts only at muscular synapses and not at the cholinergic synapses of the central nervous system (curare does not cross the blood-brain barrier), a victim of curare poisoning may be aware of what is happening until the very end. Consequently, the victim can feel the paralysis progressing but is quickly unable to move, call out or gesture. If artificial respiration is performed throughout, the victim usually recovers without ill effects.

Medical use

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. For surgical operations and 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 Läwen, in 1912, but it became commonplace only after trials by Dr Harold Griffith and Enid Johnson of Montreal, Canada in 1942. Curare was also used to treat the paralysis caused by tetanus because the muscle relaxant counters the contractions caused by the tetanus toxin.