Calabar beans are the dried ripe seeds of Physostigma veneno-sum half containing not less than 0.15% alkaloids, belonging to family Leguminosae (Papilionaecae).
PHYSOSTIGMA
Synonyms
Calabar bean, Ordeal bean, Chop nut.
Biological Source
Calabar beans are the dried ripe seeds of Physostigma veneno-sum half containing
not less than 0.15% alkaloids, belonging to
family Leguminosae (Papilionaecae).
Geographical Source
The plant is a perennial woody climber and grows in West
Africa, Old Calabar, India and Brazil.
History
The plant came into notice in 1846 and was planted in the
Edinburgh Botanical Gardens, where it grew into a strong perennial creeper. The
natives of Africa employ the bean as an ordeal owing to its very poisonous
qualities. They call it esere, and it is given to an accused person to eat. If
the prisoner vomits within half an hour he is accounted innocent, but if he
succumbs he is found guilty. A draught of the pounded seeds infused in water is
said to have been fatal to a man within an hour.
Characteristics
It is a great twining climber, pinnately trifoliate leaves,
pendulous racemes of purplish bean-like flowers; seeds are two or three
together in dark brown pods about 6 inches long and kidney-shaped, thick, about
1 inch long, rounded ends, roughish but a little polished, and have a long scar
on the edge where adherent to the placenta. The seeds ripen at all seasons.
Chemical Constituents
Drug contains 0.1–0.2% indole alkaloids of which half is
physostigmine known also as eserine (a crystalline solid, white or pinkish
coloured, readily soluble in alcohol, sparingly soluble in water) and is the
important alkaloid. The other alkaloids are eseramine, geneserine and
physovenine. Physostigmine the major alkaloid is present in cotyledons up to
0.04–0.3%, Physostigmine is methyl carbamide acid ester of eroline. These
alkaloids are pyrrolidineindoline derivatives. Calabar beans also contain
stigmasterol.
Uses
Mainly used for diseases of the eye; it causes rapid
con-traction of the pupil and disturbed vision. Also used as a stimulant to the
unstriped muscles of the intestines in chronic constipation. Its action on the
circulation is to slow the pulse and raise blood pressure; it depresses the
CNS, causing muscular weakness; it has been employed internally for its
depressant action.
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