Hypoglycaemic and hypotensive effects of Harpephyllum caffrum Bernh ex CF Krauss (Anacardiaceae) stem-bark aqueous extract in rats.

The stem bark of Harpephyllum caffrum Bernh ex CF Krauss (family: Anacardiaceae) is used traditionally in African folk medicine to manage, control and/or treat an array of human ailments, including diabetes mellitus and hypertension. In order to scientifically appraise some of the anecdotal, folkloric and ethnomedical uses of Harpephyllum caffrum, this study was undertaken to examine the hypoglycaemic and hypotensive effects of Harpephyllum caffrum stem bark aqueous extract (HCE) in rat experimental paradigms. The hypoglycaemic effect of the plant extract (HCE) was examined in normal and diabetic rats, using a streptozotocin (STZ)-induced diabetes mellitus model. Hypertensive, Dahl salt-sensitive rats were used to investigate the hypotensive (antihypertensive) effect of the plant extract. Chlorpropamide (250 mg/kg po) was used as the reference hypoglycaemic agent for comparison. Acute oral administrations of the plant extract (HCE, 50-800 mg/kg po) caused dose-related, significant (p < 0.05- 0.001) hypoglycaemia in normal (normoglycaemic) and STZ-treated diabetic rats. Furthermore, acute intravenous administrations of the plant extract (HCE, 25-400 mg/kg iv) produced dose-dependent, significant reductions (p < 0.05-0.001) in systemic arterial blood pressures and heart rates of the hypertensive, Dahl salt-sensitive rats used. Although the exact mechanisms of action of the plant extract still remain obscure at the moment, it is unlikely that the plant causes hypotension in the mammalian experimental animal model used, via the cholinergic mechanism, since its hypotensive effect was resistant to atropine pretreatment. The numerous polyphenolic compounds and flavonoids present in the plant are speculated to account for the observed hypoglycaemic and hypotensive effects of the extract. However, the findings of this experimental animal study indicate that the stem-bark aqueous extract of H caffrum possesses hypoglycaemic and hypotensive properties, and thus lend pharmacological support to the suggested folkloric, anecdotal and ethnomedical uses of the plant in the management and/or control of adult-onset type 2 diabetes mellitus and hypertension in some rural communities of southern African.