Piperaceae

West African black pepper or Ashanti pepper

L The black berries are a much-used spice. The pepper is used externally as a counter-irritant or in a stimulating ointment, and internally as a stomachic and carminative. The pulverized grains are useful as an insecticide.

C Chromatographic analysis of the fruits has revealed the amides piperine, jV-iso-butyloctadeca-ira¬ęs-2-trans-4-dienamide, sylvatine, Aa,/3-dihydro-piperine, tricho-stachine and a new naturally occurring amide, Aa ,/3-dihydro-piperlonguminine (Addae-Mensah et al., 1977a, b). In the roots, piperine, trichostachine, and in the leaves, dihydrocubebin, a new naturally occurring lignan, have been reported (Dwuma Badu, 1975d). Earlier, 0.2% of a lignan derived from shikimic acid, aschantine and another lignan, which has been named yangambine, had been reported by Hanzel et al. (1966). An essential oil composed of terpenes (phellan-drene, pinene, limonene has been obtained from the berries (1-2.4%) (Dwuma Badu et al., 1975d, 1976a; Tackie et al., 1975a; Raina etal., 1976).

P Some of the constituents have been reported to have antimicrobial, anticonvulsant, antihypertensive, sedative, tranquillizing and insecticidal properties (Fong, 1972; Addae-Mensah et al., 1977a, b). Small quantities act as a gastric stimulant and carminative, increase the flow of saliva and gastric juice, have diuretic and diaphoretic properties and act as a nervous stimulant. They also have bactericial and insecticidal action. In high doses, they are irritating to the skin and mucosae and can produce convulsions and haematuria (Paris and Moyse, 1967, Vol. II, p. 113). A derivative based on piperine, isolated from P. nigrum seeds is used in Chinese medicine as an antiepileptic (Xiao, 1983).

Anacardium occidentale L. ANACARDIACEAE

(See also Chapter 2.)

P An essential oil obtained by steam distillation from the leaves of A. occidentale produced in rats, in doses of 150-300 mg/kg of a 5% oil emulsion given intraperi-toneally, a dose-related decrease of spontaneous motor activity and potentiated sodium pentobarbitone-induced hypnosis. Rota rod performance was decreased and further investigations suggested a CNS depressive action of tranquillizer type similar to, but lower than that of chlorpromazine. The essential oil possesses, however, an additional analgesic action (Carg and Casera, 1984).

Sedation, decreased spontaneous motor activity, loss of muscle tone, potentiation of barbitone sleeping time and ether anaesthesia were also seen with the xanthones from Calophyllum inophyllum Guttiferae (see Chapter 5).

Ill Peripherally acting depressants of the CNS (a) Local anaesthetics

Local anaesthesia is a selective inhibition of conduction in the afferent or sensory nerves and endings resulting in the loss of the sensations of pain, pressure and temperature in localized areas of the body, especially the skin and mucous membranes. Local anaesthetics may act by preventing the liberation of acetylcholine from the preganglionic nerve endings thus blocking nerve conduction when applied locally. In low concentrations local anaesthetics mainly prevent the generation and production of nerve impulses. Their site of action is the cell membrane which they depolarize in changing the permeability to potassium and sodium ions. They can produce a depressant effect on the heart and a relaxation of the smooth muscles, which can be explained by the ganglioplegic action but can also be due to a direct stabilizing effect on the axonic membrane (Lechat et al., 1978, pp. 582-3). Local anaesthetics are broken down in the liver to non-toxic constituents. Overdoses may lead to tremor, restlessness and convulsions (Burgen and Mitchell, 1972; Turner and Richens, 1978).

The local anaesthetic activity of cocaine from Erythroxylum coca (Erythroxylaceae) has long been known. Local anaesthetic action has also been recorded in Cassia absus (Caesalpiniaceae) through chaksine and isochaksine. The majority of the other plants with local anaesthetic action seem to act through the ANS. The local anaesthetic activity of Jatropha podagrica is attributed to tetramethylpyrazine and that of Erythrophleum guineense to cassaine. Indole alkaloids with local anaesthetic action have been reported in Mitragyna spp. (Rubiaceae) (mitraphylline), Pausiny-stalia johimbe (Rubiaceae) (yohimbine) and Voacanga africana (Apocynaceae) (voa-cangine) and a local anaesthetic steroid alkaloid has been noted in Picralima nitida (Apocynaceae).

Erythroxylum coca Lam. ERYTHROXYLACEAE

Cocaine plant

L Cultivated in West Africa (Hutchinson and Dalziel, 1954, p. 356), the astringent leaves are used locally in India as a stimulant and masticatory (Chopra et al., 1956, p. 111).

C The leaves contain the alkaloid cocaine which is also present in the bark and seeds. In India, the leaves contain 0.4-0.8% of total alkaloids, largely cocaine (methylben-zoylecgonine), but also other pseudotropanol derivatives such as cinnamylcocaine, truxillines and tropacocaine (benzoylpseudotropanol), as well as some monocyclic A/-methylpyrrolidine derivatives (Henry, 1949, pp. 93-104; Paris and Moyse, 1967, p. 283-4).

P Cocaine has pharmacological actions on the nervous and cardiovascular systems similar to those of other local anaesthetics but it blocks the uptake of catecholamines into nerve terminals and so has sympathomimetic properties. It produces surface anaesthesia on the eye and mydriasis. Despite vasoconstrictive properties it is readily absorbed from mucous membranes and is used for anaesthesia of respiratory passages (bronchoscopy) but more suitable drugs are now available. Cocaine stimulates the CNS and has been used as a stimulant in neurasthenia but must be given under strict medical control as it is habit-forming. It produces a short spell of intellectual stimulation and euphoria followed by depression. Large doses cause convulsions followed by central paralysis and finally by failure of respiration (Burgen and Mitchell, 1972; Turner and Richens, 1978).

When E. coca leaves (or powder) (5-10 g) are taken orally by human subjects cocaine is immediately detected in the blood by gas chromatographic mass spectrometry. It reaches peak concentrations after 40 min to 1 h and persists in the plasma for more than 7 h (Holmstedt et al., 1979).

Cassia absus L. CAESALPINIACEAE

Four-leaved senna

L The seeds are used in West Africa as a fomentation in ophthalmias and are also used to treat ringworm infections. The leaves are used in Northern Nigeria and in Togo as a dressing for ulcers and swellings believed to be of venereal origin. In India the leaves are employed to treat asthma and the seeds are used for the treatment of ringworm and ophthalmias (Chopra et al., 1956; Oliver, 1960).

C The seeds contain a fixed oil and a toxalbumin absin, similar to abrin from Abrus precatorius, as well as two alkaloids, chaksine and isochaksine. /3-Sitosterol and /3-sitosterol glucoside are found in the seed oil (Oliver, 1960; Qureshi et al., 1964). Chrysophanol, aloe emodin, chaksine and isochaksine have been isolated from the roots and in addition to the two alkaloids, quercitin and rutin have been found in the leaves (Siddiqui and Ahmad, 1935; Oliver, 1960; Krishna Rao et al., 1979).

P The pharmacology of chaksine and isochaksine has been extensively studied by Pradhan et al. (1953), Bukhari and Khan (1963) and Khan et al. (1963). Both alkaloids proved to have a local anaesthetic action on guinea pig skin when administered intradermally. The action is inferior to that of procaine, which proved to be 3.6 times more active than chaksine and 1.7 times more active than isochaksine. The anaesthetic action was confirmed in Man. By intradermal injection they produce histamine-like reactions. Chaksine and isochaksine also have distinct hypotensive and depressant effects on the parasympathetic nerve terminals of the bronchi, intestines and bladder (an action comparable to atropine) and also have a ganglioplegic and curariform action, isochaksine being generally somewhat less active than chaksine. Thus, both have a general depressive action on the CNS and the neuromuscular junctions (Pradhan et al., 1953). Strong anti-5-hydroxytryp-

tamine action has also been reported. The LD50 for chaksine given perorally to mice was around 70 mg/kg; in frogs it was 100 mg/kg. Chaksine and isochaksine also have an antibacterial action (Gupta and Chopra, 1953). Chaksine inhibits the growth of Staphylococcus aureus and of Bacillus haemolyticus at dilutions of 1:100000 (Cheema and Priddle, 1965).

Jatropha podagrica Hook. EUPHORBIACEAE

L A native of Central America, this species is much cultivated in West Africa. The local medicinal uses in Ghana and Nigeria are as an antipyretic, diuretic, choleretic and purgative; stems and roots are used as chewing sticks (Irvine, 1961). ,7. curcas seed oil is used in local medicine in dropsy, sciatica, paralysis, worms and skin diseases (Oliver, 1960).

C Tetramethylpyrazine has been obtained from the stem of J. podagrica. This substance had formerly been reported to be present in fermented soya beans, cocoa beans and tobacco smoke (Odebiji, 1978). In J. curcas a toxalbumin (curcin) and small quantities of glycosides have been reported (Chapter 2, this volume).

P Tetramethylpyrazine demonstrated antibacterial activity (Odebiji, 1978). In anaesthetized cats it produced depressor effects, reduced the heart rate and blocked neuromuscular transmissions and appeared to have a spasmolytic activity on smooth muscles (Ojewole, 1980; Ojewole and Odebiji, 1980). Further studies confirmed blockage of adrenergic and cholinergic transmission by tetramethylpyrazine. The compound depressed and abolished the electrically evoked contractions of the chick oesophagus, rabbit duodenum and guinea pig vas deferens in vitro. It also inhibited the electrically induced contraction of the rat isolated hemi-diaphragm and of the cat's nictating membrane in vivo. Apart from its possible central effects, and those on the cardiac muscle and blood vessels, it could be suggested, from the results obtained in this study, that the hypotensive effect in experimental animals is likely to be contributed to by, or mediated via, its local anaesthetic (membrane stabilizing) activity. Through this action, the drug probably acts to block sympathetic and parasympathetic neurones and ganglia (Ojewole, 1981).

Tetramethylpyrazine has a number of other pharmacological actions. A main central effect was found to be tranquillization and sedation (Ojewole and Odebiji, 1984).

In China, tetramethylpyrazine originating from plants is used in the treatment of occlusive cerebral vessel diseases such as cerebral embolism (Xiao, 1983).

Plants having local anaesthetic action which are described in Chapter 2 (The cardiovascular system) are listed in Table 3.5.

(b) Neuromuscular blockers (curare action) and anticonvulsants

Plants which act on the neuromuscular junctions do so through the curare alkaloids. When introduced into the bloodstream the curare alkaloids act by interrupting the transmission of the nerve impulse at the neuromuscular junctions thus producing a profound and progressive paralysis of the voluntary movements. Continued administration leads to paralysis and finally death through paralysis of

Table 3.5. Plants with local anaesthetic action which are described in Chapter 2

Plant Family

Active constituent(s)

Part(s) used

Action on nervous system

References

Picralima nitida Apocynaceae

Voacanga africana Apocynaceae

Pausinystalia johimbe Rubiaceae

Corynanthe pachy ceras Rubiaceae

Mitragyna stipulosa Rubiaceae

Akuammine, akuammidine

Voacangine

Yohimbine

Corynanthine

Mitraphylline, rhynchophylline

Stem- and rootbark

Stem- and rootbark

Bark

Bark

Rootbark

Local anaesthetic: stembark equivalent to cocaine, rootbark threefold that of cocaine hydrochloride

Local anaesthetic and analgesic

Local anaesthetic

Mild local anaesthetic

Local anaesthetic

Adrenergic action: Chapter 2

Adrenergic action: Chapter 2

Adrenergic action: Chapter 2

Adrenergic action: Chapter 2

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