Evaluation of six plant species used traditionally in the treatment and control of diabetes mellitus in South Africa using in vitro methods

CONTEXT

Numerous plants are used by the local communities of South Africa for the treatment and management of type II diabetes.

OBJECTIVES

For this study, we undertook a survey of the plants sold for the management of diabetes in the town of Newcastle, South Africa. Identified plants were subsequently evaluated for their in vitro antidiabetic activity.

MATERIALS AND METHODS

Plants were identified through an interview with a herbalist at the market. Antidiabetic activity of extracts of purchased plants was evaluated using in vitro α-amylase and α-glucosidase activity, as well as islets of Langerhans excretory activity.

RESULTS

Senna alexandrina Mill. (Fabaceae), Cymbopogon citrates Stapf. (Poaceae), Cucurbita pepo L. (Cucuribitaceae), Nuxia floribunda Benth. (Stilbaceae), Hypoxis hemerocallidea Fisch. and Mey (Hypoxidaceae), and Cinnamomum cassia Blume (Lauraceae) were identified. The hexane extract of S. alexandrina (EC50=0.083 mg/ml), ethyl acetate extract of H. hemerocallidea (EC50=0.29 mg/ml), and methanol extracts of Cymbopogon citratus (EC50=0.31 mg/ml) and Cinnamomum cassia (EC50=0.12 mg/ml) had the highest α-amylase inhibitory activity, albeit lower than acarbose (EC50=0.50 mg/ml). All the plants had good α-glucosidase inhibitory activity (>50%) with the exception of some methanol (Cinnamomum cassia, N. floribunda, and Cymbopogon citratus) and acetone extracts (Cucurbita pepo and N. floribunda). Only the H. hemerocallidea acetone extract had an insulin stimulatory effect (2.5 U/ml at 8 μg/ml).

CONCLUSION

All the evaluated plants demonstrated inhibitory activity against the specific GIT enzyme systems evaluated. Only H. hemerocallidea had insulin secretory activity, adding evidence to the traditional use of these purchased plants in the management of the type II diabetic post-prandial hyperglycemia.

Pharmacological actions of Heteromorpha trifoliata ("dombwe") on rat isolated muscle preparations

OBJECTIVE

To investigate the effects of Heteromorpha trifoliata on rat uterine and skeletal muscle.

DESIGN

Laboratory based study using experimental animals. Investigating the effects of the plant extract and agonists on isolated muscle preparations.

SETTING

Department of Physiology, University of Zimbabwe.

SUBJECTS

28 Sprague-Dawley rats.

MAIN OUTCOME MEASURES

Amplitude of contraction of uterine smooth muscle and skeletal muscle.

RESULTS

Experiments were performed on the isolated rat uterus preparation in which strips of myometrium were placed in tissue baths filled with Kreb's solution. The aqueous extract of the root bark of Heteromorpha trifoliata ("dombwe") contracted the rat uterus. The contractions were not antagonised by atropine but were blocked by both cyproheptadine and verapamil. In addition, "dombwe" induced a contracture of the rat diaphragm muscle in the presence of alcuronium.

CONCLUSIONS

The contractile effects on the uterus appear to involve stimulation of 5-HT2 receptors leading to an increase in calcium influx into the smooth muscle cell. Promotion of calcium influx could also explain the effects observed on the skeletal muscle preparation since the contracture induced by "dombwe" occurred in the presence of the nicotinic antagonist, alcuronium. In view of the effects of "dombwe" on other smooth muscle preparations (from previous work) it appears that the pharmacological profile of the crude aqueous extract of the root bark of Heteromorpha trifoliata is complex and suggestive of the presence of more than one active ingredient.