L The seeds and bark are used in Nigeria for their antipyretic, tonic and purgative action (Dalziel, 1937).

C Three tetraoxygenated xanthones (l-hydroxy-3,7,8-trimethoxyxanthone, 1,7-dihydroxy-3,8-dimethoxyxanthone and swertioside) have been isolated from the leaves of A. vogelii collected in Zaire (Chapelle, 1974).

P The medicinal properties attributed to the plant are believed to be due to the synergistic activity of the xanthones (reported to have MAOI action by Suzuki et al. (1981), tetraoxygenated xanthones (which have anticonvulsant properties) and seco-iridoids (which are stimulants and stomachics) (Ghosal et al., 1973; Chapelle, 1974).

Centella asiatica (L.) urb. Hydrocotyle asiatica L. UMBELLIFERAE

Indian pennywort

L An infusion of leaves and stems has been used in India for the treatment of leprosy and other skin diseases, and as a diuretic (Indian Pharmaceutical Codex). Large doses are said to have a narcotic effect.

C Asiaticoside, a glycoside of a genin composed of a pentacyclic triterpenic acid, was isolated from the Madagascar plant by Bontemps (1942). Bhattacharya and Lythgoe (1949) found no asiaticoside in the Sri Lankan plant, but reported the presence of a related compound, centelloside, and the triterpenic acids centoic and centellic acid (Boiteau et al., 1949; Boiteau and Ratsimamanga, 1956; Oliver, 1960). Appa Rao et al. (1969) found in Indian plants two free terpenic acids, brahmic and isobrahmic acid, two saponins, brahmoside and brahminoside (tri- and tetraglycosides of brahmic acid) and also betulic acid and stigmasterol. The saponins were found to be different from asiaticoside found in the Madagascar plants. Dutta and Basu (1967) had isolated and identified asiatic acid in an Indian variety of Centella asiatica and the presence of asiaticoside, myoinositol and oligosaccharide of centellose in this variety has also been reported. Finally, it has been shown that, depending on the habitat, the saponins can be of two types, the more common one containing asiaticoside and medacanoside, and the less common one showing the additional presence of arabinose in the saponins, thus forming brahmoside and brahminoside. Sapogenins and flavonoids were the same in both varieties (Rao and Seshadri, 1969).

P Asiaticoside had been found to be active in the treatment of leprosy (by dissolving the waxy coating of Mycobacterium leprae whilst an oxidized form, oxyasiaticoside, inhibited the growth of tubercle bacillus in vitro and in vivo (Boiteau et al., 1949). In clinical trials, Appa Roa et al. (1969, 1973) studied the effect of the plant on the general mental ability of mentally retarded children and its anabolic effect on normal healthy adults. They found that in 30 mentally retarded children (free from epilepsy and other neurological conditions) a significant improvement in both general ability and behavioural pattern was obtained when the drug was administered for a period of 12 weeks. In 43 normal adults the mean levels of blood sugar, serum cholesterol, total protein and vital capacity were increased by the drug and the mean levels of blood urea and serum acid phosphatase were decreased (Appa Rao et al., 1973).

Strychnos alkaloids. These are known to be analeptic and convulsant and are medullary stimulants. As analeptics they were used to overcome depressions due to overdoses of barbiturates or morphine, but this is now mostly abandoned because of their high toxicity. They act on the spinal cord by antagonizing or blocking postsynaptic inhibitions. Brucine has a similar action to strychnine but is fifty times less toxic. Picrotoxin, obtained from the Indian Anamirta paniculata, is a medullary stimulant in small doses and is used in preference to strychnine to counteract barbiturate and bromide poisoning. The West African Dioscorea dumetorum (Dio-scoreaceae) has a picrotoxin-like convulsive action on the medulla.

Strychnos spp. LOGANIACEAE

L The local uses of the Strychnos spp. vary greatly. Some, like S. usambarensis, S. camptoneura, S. splendens and S. angolensis, seem not to be used in local medicine. The seeds of 5. densiflora were used in trial by ordeal and the fruits of 5. aculeata as a fish poison (Dalziel, 1937). The alkaloids of the latter species were studied by Mirand etal. (1979).

C Among the West African Strychnos spp. only a few were found to contain small quantities of alkaloids with convulsant effects, whereas muscle relaxing alkaloids seem to be present in more West African spp.

The first isolation of a convulsive alkaloid from African Strychnos spp. was achieved by continual pharmacological screening for convulsive and muscle relaxant effects in the East African S. icaja Baill. (Sandberg et al., 1969a, b). This led also to the detection of 4-hydroxystrychnine in that species. From the rootbark of 5. aculeata Sol., Sandberg et al. (1969b) isolated strychnofendlerine and N-acetylstrychnosplendine as well as traces of brucine. The muscle-relaxing effects seem to be limited to extracts of the seeds and the pericarp of the fruit and was later considered to be weak.

As a result of further screening, new tertiary indole alkaloids with a pronounced muscle-relaxant effect but producing clonic convulsions in high doses were found in other species (Sandberg and Kristianson, 1970; Sandberg et al., 1971; Verpoorte and Bohlin, 1976; Rolfsen and Bohlin, 1978).

In 1975 Bouquet and Fournet (1975b) reported that the only African Strychnos spp. with over 0.5% of total alkaloids were S. camptoneura Gilg & Busse, S. splendens Gilg, S. angolensis Gilg and S. usambarensis Gilg. P Verpoorte and Bohlin (1976) screened 11 African Strychnos species for muscle relaxant and convulsant effects. They reported strong muscle relaxant effects in 5. usambarensis, S. afzelli Gilg, S. barteri Sol. and S. longicaudata Gilg whilst in S. aculeata Sol., S. malacoclados Wright and S. spinosa only a weak effect was noted.

Further details are given on five of the very many West African Strychnos spp.

Strychnos camptoneura Gilg & Busse syn. (Scyphostrychnos talbotti Moore, S. psit-taconyx Duvign.) LOGANIACEAE

C Sandberg et al. (1971), in studying the muscle relaxant properties of stem- and rootbark collected in the Cameroons, found 11 alkaloids, the main ones being serpentine and alstonine. Koch et al. (1972) and Garnier et al. (1974) found five new alkaloids in the bark of specimens from the Ivory Coast; these were identified as retuline, camptine, camptoneurine, camptinme and N-oxyretuline.

P Verpoorte and Sandberg (1971) reported muscle relaxant activity in the stem- and rootbark of S. camptoneura Gilg & Busse.

Strychnos usambarensis Gilg syn. (S. micans Moore, S. cooperi Hutch. & Moss)

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