Chemical and pharmacological studies of marketed traditional drugs

MESFIN BOGALE*, B.K. NOAMESI** and ERMIAS DAGNE*

*Department of Chemistry
Faculty of Science, Addis Ababa University
P.O. Box 1176, Addis Ababa, Ethiopia

**Department of Pharmacology
Faculty of Pharmacy
University of Science and Technology
Kumasi, Ghana.

Introduction

Most of the medicaments used in the traditional medicine of Ethiopia, as indeed in many other countries, are of plant origin. These traditional medicines are obtained in most cases from healers. However, the very common medicaments are obtainable from vendors.

In most markets one does not fail to find a corner which could be considered as an "open pharmacy" and where medicinal plant preparations are spread out to attract the attention of customers. Vendors do not usually prescribe as the customers are quite knowledgeable about the type of drug they wish to purchase.

A survey of 19 medicinal plant markets of Central Ethiopia (Kloos et al. 1978) identified over 40 common medicinal plants sold routinely. This survey showed that Ethiopia has a rich medicinal plant resource. The interdisciplinary studies of clinicians, chemists, pharmacists, botanists agronomists and anthropologists is necessary to develop more efficient uses for these potential resources. Table 1 summarises the results of the survey of Kloos et al.

The proper authentication of medicinal plants and identification of the active ingredients, is invaluable in the assessment of the pharmaceutical value of the traditional medicines. Although the usage of most of the marketed traditional drugs does not require special knowledge, there are instances where overdosage leads to toxic effects, particularly in the use of anthelmintics. Pharmacological studies, therefore, help not only to determine efficacy of these traditional preparations, but also to establish required dosages.

In this paper, we report the results of a study on one of the marketed drugs of Ethiopia. In the indigenous system of medicine in Central Ethiopia, the roots of Taverniera abyssinica (Leguminosae) are known in the Amharic language as 'Dingetegna' signifying "medicine for sudden illness'. The roots are chewed to alleviate severe stomach pain and fever.

T. abyssinica is an endemic species occurring in Ethiopia and grows up to 2 m high in bushland or on limestone, at altitudes between 1700 and 2200 m. Taverniera belongs to a relatively small genus containing only 15 species found in arid regions, from Egypt to India (Thulin, 1983). Three other species are also known to occur in Ethiopia.

Phytochemical investigations of the roots have revealed the presence of a number of compounds including the isoflavonoids formononetin, afrormosin and the pterocarpans medicarpin and 4-hydroxymedicarpin (Duddeck et at., 1987). It has also recently been shown that extracts of the roots of this plant exhibit antipyretic and analgesic properties (Dagne et al, 1990).

The present investigation has been undertaken to evaluate the spasmolytic and other pharmacological activities of the extract of this plant, in order to establish an ethnopharmacological basis for its use in traditional medicine.

Materials and methods

Plant material

The plant material used in this study was purchased from the main market in Addis Ababa from traditional medicine vendors. For botanical authentication of the plant material as T. abyssinica and for voucher specimens see Duddeck et al. (1987).

Extraction

The powdered root (100 g) of T. abyssinica was soaked in 75% ethanol in water for 24 hrs. The concentrated extract was further extracted with butanol. The butanol extract was successively refluxed for 20 min. each with ethyl acetate, acetone and ethanol. The ethanol portion was used to test on the different models. The other extracts were devoid of pharmacological activity.

Pharmacological tests

Four experimental models were employed to investigate the effects of the extract: anti-ulcer, antiasthmatic (in vivo), oxytocic (both in vivo and in vitro) and the isolated guinea-pig ileum. The extract was found to have an effect only on the isolated guinea pig ileum.

Isolated guinea-pig ileum

Adult guinea-pigs weighing 250-350 g were used. Heal segments (ca. 2-3 cm long) were taken from the caecal end. The muscle was suspended in warm (37° C) Tyrodes solution aerated with atmospheric air in a 20-ml organ bath. Contractions of the smooth muscle were monitored by means of the Ugo Basile isotonic transducer with 1 g tension and recorded on the Ugo Basile Gemini 7070 two-channel recorder at a chart speed of 5-mm/min. The tissue was allowed to equilibrate in Tyrode's solution for 30 min. Control contractile response were obtained for acetylcholine. A contact time of 30 sec. and time cycle of 3 min. was maintained. The extract was then introduced into 500 ml of Tyrode's solution in different concentrations. Using this solution acetylcholine-induced contractile responses were again elicited after giving 20 min. for the tissue to equilibrate every time a fresh solution containing a higher concentration of the extract was used.

In another set of experiments, the effects of the extract of the contractile response of the ileum to histamine were similarly investigated.

Statistical analysis

The given data represent mean ± S.E.M. and the statistical significance was evaluated by the Student t-test.

Results

The extract produced no changes on the resting tone of the isolated guinea-pig ileum, i.e. neither a spasmogenic action nor a relaxation of smooth muscle was observed at any of the concentrations tested. Acetylcholine at concentrations of 5, 10 and 20 ng/ml produced concentration- dependent contractions of the ileum. The acetylcholine-induced contractions were significantly (p < 0.001) antagonized by the extract at 500 and 800 ng/ml. Fig. 1 illustrates a typical effect of the extract on the ileal response to acetylcholine and the results are presented in Table 1.

In the presence of the extract, maximal responses to acetylcholine could not be reestablished by increasing the concentrations of acetylcholine. Histamine at 10, 20 and 40 ng/ml also contracted the guinea-pig ileum in a concentration-dependent manner. The inhibitory effects of the extract on the isolated guinea-pig ileum contractions to histamine are illustrated in Fig. 2 and the results are presented in Table 2. As was observed for acetylcholine, in the presence of the extract, maximal responses to higher histamine concentrations were also not attained.

Discussion

Spasms of the gastrointestinal tract and gastric hyperacidity contribute to the symptoms of stomachache. In orthodox pharmaceutical preparations, such as, belladonna extracts, containing alkaloids of the atropine type, are often included in formulations for stomach ailments, because of their spasmolytic actions against acetylcholine-induced spasms (Weimer, 1980). Histamine mediates gastric acid secretion, acting through the H receptors and has been shown to be responsible for gastric pain, particularly in ulcers. To antagonize the histamine, gastric activity H receptor antagonist drugs like cimetidine, have been designed (Douglas, 1980).

Our present preliminary pharmacological investigations of T. abyssinica have illustrated the ability of the extract to antagonize the smooth muscle spasmogenic actions of both acetylcholine and histamine, two of the most important spasmagens responsible for hyperactivity of the gastrointestinal tract. The non-attainment of the maximum control response of acetylcholine and histamine in the presence of the extract suggests the non-competitive nature of the antagonism.

The above findings show that the extract of this plant possesses analgesic and antipyretic properties, confirming the significance of this traditional drug in ethno-medicine.

Acknowledgements

This work was supported by a grant from the Swedish Agency for Research Cooperation with Developing Countries (SAREC).

References

Dagne, E., Yenesew, A., Capasso, F., Mascolo, N., Pinto, A. and Autore, G. (1990). Ethiopian Med. J. (in press).

Douglas, W.W. (1980). "Histamine and 5-HT and their antagonists". In Gilman, A.G., Goodman, L.S. and Gilman, A. (Eds), The Pharmacological Basis of Therapeutics, Macmillan Publishing Co., New York.: 609 - 646.

Duddeck, H., Yenesew, A. and Dagne, E. (1987). Bull. chem. Soc. Ethiopia 1: 36-41.

Kloos, H., Tekle, A., Yohannes, L.W., Yosef, A. and Lemma, A. (1978). Ethiopian Med. J. 16: 33-43.

Thulin, M. (1983). Opera Bot. 68 : 186-188.

Weimer, N. (1980). "Atropine, scoplolamine and related anti- muscarinic drugs". In Gilman, A.G., Goodman, L.S. and Gilman, A. (Eds), The Pharmacological Basis of Therapeutics. Macmillan Publishing Co., New York: 120-137.

Fig.1. Typical trace showing the contractile responses of the guinea-pig ileum. 'A' shows control responses induced by ACh 5, 10, 20, 40, 80 and 160 ng/ml and 'B' shows responses of the ileum for ACh 0.08, 0.16, 0.32, 0.64, 1.28 and 2.56 ug/ml in the presence of 500 ug/ml of the extract.

Fig.2. Typical trace showing the contractile responses of the guinea-pig ileum. 'A' shows control responses induced by histamine 5, 10, 20, 40, 80 and 160 ng/ml and 'B' shows responses of the ileum for histamine 0.08, 0.16, 0.32, 0.64, 1.28, 2.56 and 5.12 ug/ml in the presence of 500 ug/ml of the extract.

Table 1: Some traditional medicinal plants marketed in Ethiopia

Table 2: Traditional medicinal drugs available at the market of Addis Ababa according to a cursory survey conducted in February 1990.