Curare

Generality

Curare is a poisonous plant extract, obtained from the barks and roots of various plant species typical of the Amazon rainforest and South America. It is used by the Indians as an arrow poison for hunting and war.

Traditional Uses

The curare is obtained by extraction from suitably crushed vegetable sources, by percolation in cold water followed by repeated boiling of the leachate, until an ideal rubbery and blackish concentrate is obtained to be placed on the tip of a slender blowpipe arrow.

The animals hit by the poisoned dart quickly fall to the ground paralyzed and, while remaining conscious, they die after a few minutes of respiratory paralysis. In spite of this, man can easily eat game, as the curare is practically inactive by mouth (the amount absorbed is minimal), while it has immediate effect when it enters the blood.

There are different techniques for preparing curare, just as the plant sources are wisely chosen from those belonging to the genus Strychnos (fam. Loganiaceae) and Chondodendron (fam. Menispermaceae). The plants belonging to these two families contain alkaloids that are different in structure but with a very similar pharmacological activity: curare-induced muscle paralysis depends on the ability of these substances to block the interaction between acetylcholine (ACh) and its receptor.

Action mechanism

The transmission of the nerve impulse at the level of the neuromuscular plaque occurs thanks to the release of ACh from the presynaptic nerve termination; after its release, ACh binds to receptors in the postsynaptic membrane, whose depolarization triggers the contraction of the muscle fiber. By blocking the passage of the nerve impulse at the level of the neuromuscular plates, the muscle becomes paralyzed; curare-induced muscle paralysis is progressive and first affects the short muscles of the head and neck, then the short muscles of the limbs, then the long muscles of the legs and arms and finally the intercostal muscles until the paralysis of the diaphragm, with consequent asphyxia for stop breathing.

Therapeutic uses

In the past, curare was used to attenuate tetanus-induced muscle spasms and, in more recent times, as a muscle relaxant during surgical procedures (it facilitates surgical operations and reduces the amount of anesthetic used; the patient's respiratory activity must be maintained through artificial equipment).

Today, curare as such is no longer used for the inconstancy of its composition and for the availability of more effective and less expensive drugs, some of which are structurally derived from its components.