Physostigma

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.

                      Physostigma venenosum

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.