Family Menispermaceae A L de Jussieu 1789 nom conserv the Moonseed Family

Physical description: The family Menispermaceae consists of 70 genera and about 400 species of tropical climbers so far known to elaborate bitter sesquiterpenes, diterpenes and benzylisoquinoline and aporphine alkaloids. In a field collection, Menispermaceae can be recognized by cross sections of the stems showing broad medullary rays, a bright yellow wood and seeds which are shaped like horseshoes. The leaves are simple, alternate, simple and without stipules. The petiole is often long and thin and the blade is often cordate. The flowers are tiny, unisexual, dioecious, and actinomorphic. In the male flowers, the sepals are tiny, in 2-4 series, imbricate, the outer smaller. The petals if present, are smaller than the sepals and the anthers are short. In the female flowers, the gynecium comprises of 3-6 carpels, which are free, sessile and contain a single ovule attached to the ventral suture. The fruits are drupaceous.

Pharmaceutical interest: Sesquiterpenes: A classical example of Menispermaceae is Anamirta paniculata Coleb. (Levant berries), the seeds of which

contain a toxic substance known as picrotoxin or cocculin. Picrotoxin is a mixture of picrotoxinin and picrotin. Picrotoxinin is a sesquiterpene specific GABAa receptor blocking agents which impede the GABAergic presynaptic inhibition of excitatory transmission of primary afferent neurones of the spinal cord (Fig. 38). Picrotoxin is toxic and as little as 20 mg induces epileptiform convulsions, myosis, and dyspnea with more or less prolonged apnea. Picrotoxin (British Pharmacopoeia, 1963), has been used in the treatment of barbiturate poisoning (3mg-6mg, intravenously) in Western medicine.

Isoquinoline alkaloids: A number of Amazonian tribes use the extract of Chondrodendron, Curarea, Sci-adotenia, Abuta, Telitoxicum, and Cissamplelos species to make arrow-poisons or curares. These curares consist of bisbenzyltetrahydroisoqui-nolines alkaloids such as (+)-tubocu-rarine, (+)-isochondrodendrine, (-)-curine, and (+)-chondrocurine which block competitively acetylcholine at nicotinic receptors at the neuromuscular junction hence causing complete relaxation of skeletal muscles and death by asphyxia. (+)-Tubocurarine which has been used to relax muscles in surgical anaesthesia (Tubocurarine Chloride, British Pharmacopoeia, 1963).

Several Menispermaceae are used to promote appetite and digestion because of their bitterness which is attributed to sesquiterpenes. The dried transverse

Fig. 39. Picrotoxin blocks the GABA receptors (GP). ENM: excitatory neurone membrane, Glu: glutamic acid, K: ketoacid, GNT: GABAergic neurone terminal, GS: GABAergic synapse, M: mitochondria, O: oxoglutamic acid, S: succinic semialdehyde. When a pair of GABA molecules bind to their sites, the receptors open and let Cl- ions enter the neurone. The resulting hyperpolarization activates the sodium channels responsible for neurone activation.

Fig. 39. Picrotoxin blocks the GABA receptors (GP). ENM: excitatory neurone membrane, Glu: glutamic acid, K: ketoacid, GNT: GABAergic neurone terminal, GS: GABAergic synapse, M: mitochondria, O: oxoglutamic acid, S: succinic semialdehyde. When a pair of GABA molecules bind to their sites, the receptors open and let Cl- ions enter the neurone. The resulting hyperpolarization activates the sodium channels responsible for neurone activation.

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(+) - Tubocurarine slices of roots of Jateorrhiza palmata Miers (Calumba, British Pharmaceutical Codex, 1954) were used to treat atonic dyspepsia whereas the dried stems of Tinospora cordifolia (Tinospora, Indian Pharmaceutical CodeX) were used to promote digestion and appetite in the form of an infusion. Weight loss phytopharmaceuticals containing Stephania tetrandra S. Moore are banned on account of their hazardous effect on the kidneys. Approximately 40 species of plants classified within the family Menispermaceae are used for medicinal purposes in the Asia-Pacific, particularly to promote urination and menses, to relieve gastrointestinal troubles, to treat fever, asthma, paralysis, rheumatism, to wash inflamed eyes, to assuage pain and to invigorate health. One might have noticed that the convulsions provoked by picrotoxin could be antagonized by the muscle-relaxing effect of bisbenzyltertrahydroquinoline alkaloids, confirming thereby the Asian belief that a poison and its antidote are inhabited in different parts of the same plant.

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